|
Sign In to gain access to subscriptions and/or personal tools.
|
CRITICAL REVIEWS IN ORAL BIOLOGY & MEDICINE |
Innate Immune Signaling and Porphyromonas gingivalis-accelerated Atherosclerosis
F.C. Gibson, III1,
H. Yumoto1,2,
Y. Takahashi1,3,
H.-H. Chou1,4 and
C.A. Genco1,5,6,*
1 Department of Medicine, Section of Infectious Diseases, and
6 Department of Microbiology, Boston University School of Medicine, Evans Biomedical Research Center, 650 Albany Street, Room 637, Boston, MA 02118, USA;
2 Department of Conservative Dentistry, Tokushima University School of Dentistry, Tokushima, Japan;
3 Department of Oral Microbiology, Kanagawa Dental College, 82 Inaokoa-cho, Yokosuka 238-8580, Japan;
4 School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan; and
5 Department of Periodontology and Oral Biology, Goldman School of Dental Medicine, Boston University Medical Center, Boston, MA, USA
Correspondence: * corresponding author, caroline.genco{at}bmc.org
 |
ABSTRACT
|
|---|
Periodontal diseases are a group of diseases that lead to erosion of the hard and soft tissues of the periodontium, which, in severe cases, can result in tooth loss. Anecdotal clinical observations have suggested that poor oral health may be associated with poor systemic health; however, only recently have appropriate epidemiological studies been initiated, with defined clinical endpoints of periodontal disease, to address the association of periodontal disease with increased risk for cardiovascular and cerebrovascular disease. Although conflicting reports exist, these epidemiological studies support this connection. Paralleling these epidemiological studies, emerging basic scientific studies also support that infection may represent a risk factor for atherosclerosis. With P. gingivalis as a model pathogen, in vitro studies support that this organism can activate host innate immune responses associated with atherosclerosis, and in vivo studies demonstrate that this organism can accelerate atheroma deposition in animal models. In this review, we focus primarily on the basic scientific studies performed to date which support that infection with bacteria, most notably P. gingivalis, accelerates atherosclerosis. Furthermore, we attempt to bring together these studies to provide an up-to-date framework of emerging theories into the mechanisms underlying periodontal disease and increased risk for atherosclerosis, as well as identify intervention strategies to reduce the incidence of periodontal disease in humans, in an attempt to decrease risk for systemic complications of periodontal disease such as atherosclerotic cardiovascular disease.
Key Words: Porphyromonas gingivalis • periodontal disease • Toll-like receptors • endothelium • innate immunity Abbreviations: ApoE = apolipoprotein E • CAM = cell adhesion molecule • CMV = cytomegalovirus • HAEC = human aortic endothelial cell • HSP = heat-shock protein • HUVEC = human umbilical vein endothelial cell • ICAM-1 = intracellular adhesion molecule-1 • IFN- = interferon- • IgA = immunoglobulin A • IL = interleukin • LPS = lipopoly-saccharide • LDLR = low-density lipoprotein receptor • MCP-1 = macrophage chemotactic protein-1 • MOI = multiplicity of infection • PAMPs = pathogen-associated microbial products • PGE2 = prostaglandin E2 • RANTES = Regulated on Activation, Normal T Expressed and Secreted • SMC = smooth-muscle cells • TLR = toll-like receptor • TNF- = tumor necrosis factor- • VCAM-1 = vascular cell adhesion molecule-1
|
INTRODUCTION
|
|---|
Periodontal disease, a complex chronic inflammatory disease that affects the periodontium, is initiated by bacteria, with incipient erosion of the attachment apparatus of the tooth. It has been reported that more than 100 million people in the US may possess measurable periodontal bone loss, making this disease one of the most common chronic infectious diseases of humans (Slade and Beck, 1999). Despite identification of over 500 different bacterial species in the oral cavity, only a relative few organisms are linked to periodontal disease; however, Porphyromonas gingivalis is the most common organism linked to adult forms of periodontal disease. Over the past 10 years, mounting evidence has accumulated supporting a role for periodontal disease and infection, with P. gingivalis as a potential risk factor for several systemic diseases, including diabetes, pre-term birth, heart disease, and atherosclerosis (Genco, 1996; Morrison et al., 1999; Dasanayake et al., 2003).
Atherosclerosis, formerly considered a condition associated with elevated circulating lipids with arterial vessel lipid accumulation, actually involves an ongoing inflammatory response. In humans, the inflammatory reactions within coronary atherosclerotic plaques are increasingly thought to be crucial determinants of the clinical course of patients with coronary artery diseases. Since numerous reviews exist detailing the development of atherosclerosis (Stary et al., 1994, 1995; Ross, 1999; Libby et al., 2002), we will not discuss the mechanisms underlying the development of atherosclerosis, other than those potentially relevant to infection-associated atherosclerosis. In various animal models of atherosclerosis, inflammation occurs simultaneously with incipient lipid accumulation in the artery wall. The stimuli that initiate and sustain the inflammatory process, however, have not been fully identified. Modified lipoproteins and local or distant infections have been proposed to contribute to the inflammatory process in atherosclerosis (Epstein et al., 1999a; Espinola-Klein et al., 2002; Libby et al., 2002). Evidence in humans suggesting that infection with P. gingivalis and periodontal disease predisposes to atherosclerosis is derived from studies demonstrating that periodontal disease pathogens reside in the walls of atherosclerotic vessels, and from sero-epidemiological studies demonstrating an association between the pathogen-specific antibodies and atherosclerosis.
The goal of this review is to discuss specifically the association between periodontal disease and the increased risk for heart disease and atherosclerosis, with particular emphasis on the putative mechanisms linking P. gingivalis infection to the acceleration of atherosclerosis. Using P. gingivalis as a model organism to study pathogen-accelerated atherosclerosis, we have demonstrated, in recent studies, that invasive bacteria are required for the acceleration of atherosclerosis, and that there is an innate immune response directed to invasive P. gingivalis, as demonstrated by the increased expression of innate immune receptors in the aorta of hyperlipidemic mice following oral challenge with P. gingivalis. We have also demonstrated that invasive P. gingivalis up-regulates the expression of chemokines and cell adhesion molecules in endothelial cells and macrophages in vitro. Furthermore, invasive P. gingivalis also up-regulates the expression of innate immune receptors on the surfaces of both endothelial cells and macrophages. Collectively, these studies have begun to define the role of specific innate immune signaling molecules in response to invasive bacterial infection, and to correlate these responses to putative mechanisms involved in microbial accelerated atherosclerosis.
|
PERIODONTAL DISEASE AND P. gingivalis
|
|---|
Periodontal diseases comprise a group of inflammatory diseases of the gingiva and supporting structures of the periodontium. P. gingivalis, a Gram-negative anaerobe, has been long considered an important pathogen associated with human periodontal disease. Currently, the underlying theme of understanding is that this organism, along with the host immune response, is critical to the destruction of the supporting structures of the teeth (Holt et al., 1988). During periodontal health, the tissues adjacent to and underneath the gingival epithelium commonly possess a modest accumulation of neutrophils that are believed to be important in clearing any transient bacteria that gain access to these tissues. However, in patients in the acute or active stage of periodontal disease, the periodontium presents with a neutrophilic cellular infiltrate that switches to a predominating monocytic and lymphocytic cellular infiltrate in chronic lesions. An understanding of the complex cellular interactions that occur during periodontal disease is critical to the definition of a mechanistic approach to the determination of the bacterial factors that might be responsible for this response. Gingival crevicular fluid obtained from periodontal disease sites have high levels of IL-1β, IL-8, and IL-10 and the chemokine RANTES (Gamonal et al., 2000), plus IL-6, transforming growth factor, PGE2, IL-2, TNF-, and interferon (IFN)- (Salvi et al., 1998). The mechanisms by which P. gingivalis stimulate cytokine and chemokine production are not well-known, but recent in vitro studies have been performed with P. gingivalis as well as with purified antigens from this organism. Results from these studies have collectively determined that the host cell type, the number of bacteria, or the amount of antigen being tested is critical to the reported observations. While a large number of different bacterial species exist in the oral cavity, it is now recognized that large numbers of bacteria (bacterial load) do not necessarily result in the biological progression from health to periodontal disease. Rather, the establishment and growth of a very few bacterial species from among those resident in the subgingival niche are apparently periodontopathic (Holt et al., 1999), including Fusobacterium nucleatum, Bacteroides forsythus, Prevotella intermedia, Treponema denticola, and P. gingivalis. P. gingivalis is essentially absent during periodontal health but, during disease progression to periodontitis, can reach a very significant percentage of the pathogenic microbiota.
Oral epithelium—more specifically, the sulcular and junctional epithelium—represents one of the initial host barriers to P. gingivalis when this organism is present in the gingival sulcus. Several studies have begun to characterize the host response of oral epithelial cells to P. gingivalis. Challenge of oral epithelial cells with P. gingivalis elicits a TNF- and IL-1β response. Additional studies have demonstrated that these cells also express cell adhesion molecules on their surface in response to P. gingivalis antigens and include ICAM-1 and VCAM-1 (Wang et al., 1999). Interestingly, work by Darveau et al.(1998) has demonstrated that gingival epithelial cells challenged with P. gingivalis LPS fail to produce IL-8; furthermore, P. gingivalis LPS stimulation functions as a potent inhibitor of subsequent E. coli LPS stimulation of IL-8. In addition to these antagonistic properties, P. gingivalis infection of gingival epithelial cells can inhibit IL-8 production in response to other bacteria present in dental plaque, including F. nucleatum (Darveau et al., 1998). This mechanism has been termed ’localized chemokine paralysis’. The nature of this inhibition is not well-understood, but may relate to the processing of P. gingivalis LPS by gingival epithelial cells. Thus, along with the ability of P. gingivalis cysteine proteinases (gingipains) to digest cytokines and chemokines, the antagonistic properties of P. gingivalis LPS and localized chemokine paralysis are all attractive mechanisms by which P. gingivalis may be able to circumvent the host response.
|
BIOLOGY OF ATHEROSCLEROSIS
|
|---|
Recent advances have established a fundamental role for inflammation in mediating all stages of atherosclerosis, from initiation through progression and, ultimately, the thrombotic complications of atherosclerosis (Libby et al., 2002). Blood leukocytes, mediators of host defense and inflammation, localize in the earliest lesions of atherosclerosis in both experimental animal models and in humans. The normal endothelium does not generally support binding of white blood cells. However, it has been demonstrated, in animal models, that early after initiation of an atherogenic diet, portions of arterial endothelial cells begin to express, on their surface, selective adhesion molecules that bind to various classes of leukocytes. Once adherent to the endothelium, the leukocytes penetrate the intima. Following residency in the arterial wall, the blood-derived inflammatory cells participate in and perpetuate a local inflammatory response. Inflammatory processes not only promote initiation and evolution of atheroma, but also contribute decisively to precipitating acute thrombotic complications of atheroma (Libby et al., 2002).
Injury to the vessel wall and the associated inflammatory response to injury are now generally recognized as the essential components of atherogenesis. The triggers that initiate and sustain the inflammatory process, however, have not been definitively identified. Among the candidate triggers are oxidized LDL (ox-LDL) and heat-shock proteins (HSPs). These components of the atheroma are believed by some investigators to elicit an inflammatory response (Epstein et al., 1999a). Patients with cardiovascular disease can develop antibodies to ox-LDL and HSPs, and, some studies, although controversial, suggest that these antibodies may play a role in causing auto-immune-induced damage to the vessel wall (Epstein et al., 2000). Another candidate trigger of both inflammatory and auto-immune responses leading to the initiation and/or acceleration of atherosclerosis is infection.
|
INFECTION AND ATHEROSCLEROSIS
|
|---|
As many as 50% of patients with atherosclerosis lack currently identified risk factors, an observation indicting that additional factors predisposing humans to atherosclerosis are as yet undetected (Vita and Loscalzo, 2002). Inflammation in the arterial vessel wall is considered to play an important role in the pathogenesis of atherosclerosis (Ross, 1999; Libby et al., 2002). Likewise, in a variety of animal models of atherosclerosis, signs of inflammation occur hand-in-hand with lipid accumulation in the artery wall. Modified lipoproteins and local or distant infections have been proposed to contribute to the inflammatory process in atherosclerosis (Epstein et al., 1999a; Espinola-Klein et al., 2002; Libby et al., 2002). Accumulating evidence has implicated specific infectious agents—including cytomegalovirus (CMV), C. pneumoniae, H. pylori, Herpes simplex virus types 1 and 2, T. cruzi, and P. gingivalis—in the progression of atherosclerosis. The observed association of infection and atherosclerosis is based primarily on epidemiological data, as well as on emerging experimental studies where animal models with defined microbial pathogens were used (Beck et al., 1998; Epstein et al., 1999b; Liuba et al., 2003; Spence and Norris, 2003; Gibson et al., 2004). Several of these micro-organisms are found in atherosclerotic lesions and can aggravate atherosclerosis in experimental models (Beck et al., 1996; Epstein et al., 1999b; Scannapieco and Genco, 1999; Liu et al., 2000; Rothstein et al., 2001; Li et al., 2002; Lalla et al., 2003; Gibson et al., 2004).
|
Chlamydia pneumoniae, CYTOMEGALOVIRUS (CMV), AND Helicobacter pylori
|
|---|
C. pneumoniae has been implicated, by serological and pathological studies, in the pathogenesis of coronary artery disease. C. pneumoniae infection might contribute to early atherogenesis, which might be associated with chronic inflammation and atherosclerosis at an early stage, even before clinical events occur (Tasaki et al., 2003). Several epidemiological studies have also reported on a possible association of various forms of vascular disease with the presence and titer of CMV antibodies (Grattan et al., 1989; Blum et al., 1998; Zhou et al., 1999; Lunardi et al., 2000). Other studies show the presence of the virus, viral antigens, or nucleic acid in atherosclerotic lesions (Melnick et al., 1983). Studies in animal models and cell-culture studies present attractive mechanisms by which CMV may play a role in atherogenesis. Several epidemiological studies have also reported on the association of H. pylori antibody titers and risk for coronary heart disease and stroke (Kahan et al., 2000; Grau et al., 2001). One recent study suggests that virulent strains of H. pylori may induce systemic inflammation, whereas avirulent strains do not and thus would not be associated with accelerated atherosclerosis (Pietroiusti et al., 2002).
|
MULTIPLE PATHOGENS/INFECTIONS
|
|---|
In addition to individual pathogens, the extent of atherosclerosis and the prognosis of patients with atherosclerosis also seem to be correlated with the number of infections to which an individual has been exposed. In a prospective study, the effects of 8 pathogens and the aggregate pathogen burden on the progression of carotid atherosclerosis were evaluated in 504 patients (Espinola-Klein et al., 2002). Elevated IgA antibodies against C. pneumoniae and IgG antibodies to Epstein-Barr virus (EBV) and HSV were associated with the progression of atherosclerosis. Infectious burden was also significantly associated with progression of atherosclerosis. The authors concluded, from this study, that the number of infectious pathogens to which an individual has been exposed contributes to the progression of carotid atherosclerosis (Espinola-Klein et al., 2002). A more recent study also demonstrated a strong association between pathogen burden and cardiovascular disease, independent of classic risk factors (Georges et al., 2003). These authors suggested that the pathogen burden could also be a predictor of coronary complications.
|
SPECIFICITY OF PATHOGEN STIMULATION TO THE INDUCTION OF ATHEROSCLEROSIS
|
|---|
Screening of human atheroma has revealed that several pathogens are frequently detected in these tissues. Interestingly, the majority of organisms reported to be in these atherosclerotic plaques are responsible not for acute infections, but rather for chronic infections. Despite these findings, limited work has been performed to address the specificity of pathogen exposure to the development of atherosclerosis. Using hyperlipidemic mice, Hu et al. observed that C. pneumoniae strain AR39 and C. trachomatis strain MoPn displayed differences in ability to accelerate atheroma deposition, since C. pneumonia AR39, but not C. trachomatis MoPn, accelerated atherosclerosis (Hu et al., 1999). Interestingly, despite differences in abilities to stimulate atherosclerotic plaque deposition, both strains were detected in the aorta of challenged mice (Hu et al., 1999). This seminal work supports the hypothesis that the host response to infection is insufficient to accelerate atherosclerosis, but that there is specificity to infection-accelerated atherosclerosis.
|
P. gingivalis INFECTION AND ATHEROSCLEROSIS
|
|---|
There is evidence to support the relationship between human periodontal disease and an increased risk for acute myocardial infarction (Beck et al., 1996; Scannapieco and Genco, 1999; Haraszthy et al., 2000). Case-control studies have demonstrated a significant correlation between cardiovascular disease and periodontal disease after adjustment for cholesterol, smoking, hypertension, social class, and body mass index (Beck et al., 1996; Scannapieco and Genco, 1999; Wu et al., 2000). While some reports have not confirmed this association, this may be due to the fact that self-reported periodontal disease was used for the analysis of the patient population (Howell et al., 2001). Several bacteria associated with periodontal disease have been detected in atherosclerotic plaque (Haraszthy et al., 2000). The primary bacterium associated with adult periodontal disease, P. gingivalis, has also been identified, by PCR and fluorescence in situ hybridization, in atheromatous plaques of two patients suffering from atherosclerosis, suggesting that these micro-organisms might be metabolically active within the atherosclerotic lesions (Cavrini et al., 2005). This is the first report supporting that metabolically active oral pathogens are present in human atheroma; however, confirmation of this observation in a larger set of patients is required, and, ultimately, bacterial culture will need to be demonstrated. Finally, serum antibodies to P. gingivalis and A. actinomycetemcomitans have also been associated with coronary heart disease (Pussinen et al., 2003).
It has been suggested that periodontal disease can lead to low-level bacteremia, an elevated white cell count, and systemic endotoxemias, which could affect endothelial integrity, metabolism of plasma lipoproteins, blood coagulation, and platelet function. Furthermore, it is well-established that infection with P. gingivalis induces local inflammation. The induction of this inflammatory response can lead to gingival ulceration and local vascular changes, which have the potential to increase the incidence and severity of transient bacteremias. Several studies have also demonstrated that patients with periodontal disease have elevated levels of systemic inflammatory mediators. Extensive periodontal disease has been associated with increased levels of C-reactive protein (CRP) (Slade et al., 2003). Moderately elevated CRP is a systemic marker of inflammation and a documented risk factor for cardiovascular disease (Teragawa et al., 2004). In a separate study, control of periodontal disease achieved with non-surgical periodontal therapy significantly decreased serum IL-6 and CRP levels (D’Aiuto et al., 2004). Recent experimental studies support that local inflammation within the artery wall may also contribute to the acceleration of atherosclerosis in response to infection with P. gingivalis. Indeed, the focus of current studies is to define the precise molecular mechanisms by which P. gingivalis infection contributes to the progression of atherosclerosis, and the links among lipids and innate immune and inflammatory responses.
|
INNATE IMMUNITY AND ATHEROSCLEROSIS
|
|---|
Innate immunity consists of the inherent immune mechanisms of a host to prevent or control an infectious challenge and is typically characterized by the activation and recruitment of monocytes and macrophages. Classically, the innate immune system was defined, in part, by cell adhesion molecules and cytokine and chemokine expression, as well as by activation of the complement system and other receptors (Janeway and Medzhitov, 2002). Activation of monocytes and macrophages and other cells, such as endothelial cells, represents an important initial step in the cascade of events leading to host response in acute and chronic inflammatory diseases. Furthermore, the inflammatory nature of cardiovascular disease and the development of atherosclerosis is well-established (Ross, 1999). The immune system is capable of making qualitatively distinct responses to different microbial infections, and recent advances are starting to reveal how it manages this complex task. Genome-encoded innate immune systems target structurally conserved pathogen-associated microbial products (PAMPs), thereby allowing immediate and, in most cases, sufficient responses to eliminate invading pathogens (Vasselon and Detmers, 2002). The recently described Toll-like receptors (TLRs) recognize a specific set of PAMPs and appear to play a key role in detecting microbes and initiating inflammatory responses (Takeda and Akira, 2005). Ligation of these receptors initiates signal transduction pathways that lead to activation of nuclear factor- B (NF-B) and subsequent expression of a wide array of inflammatory genes (Imler and Hoffmann, 2001; Underhill and Ozinsky, 2002). The best-studied of the TLRs are TLR-2 and TLR-4. As the receptor for Gram-negative enterobacterial LPS, TLR-4 is the best-characterized member of the TLR family. Enterobacterial LPS is bound in serum by LPS-binding protein (LBP), which delivers LPS to CD14, a protein that exists both in soluble form and as a glycosylphosphatidylinositol (GPI)-linked outer membrane protein (Fenton and Golenbock, 1998). CD14 physically associates with a complex including TLR-4 and an extracellular accessory protein, MD-2. Each component of this complex is required for efficient LPS-induced signaling. Several other bacterial proteins have been suggested to activate immune cells through TLR-4, including teichuronic acid, fimbriae, and HSP60 from both human and microbial sources (Beutler, 2002; Hajishengallis et al., 2002; Underhill and Ozinsky, 2002).
An array of molecules has been reported to activate innate immune responses through TLR-2, including bacterial lipopeptides, peptidoglycan, and zymosan (Asai et al., 2001; Henneke et al., 2001; Thoma-Uszynski et al., 2001; Massari et al., 2002). In addition, certain structural variants of LPS are detected by TLR-2, including LPS from P. gingivalis (Bainbridge and Darveau, 2001; Hirschfeld et al., 2001; Pulendran et al., 2001; Kusumoto et al., 2004; Zhou et al., 2005). Some of the broad ligand specificity attributed to TLR-2 may be accounted for by the observation that TLR-2 must dimerize with other TLRs to detect ligands and induce signaling. Whereas several microbial products appear capable of stimulating inflammatory responses through TLR-2 and TLR-4, to date, only single microbial targets have been identified for TLR-3, TLR-5, and TLR-9. TLR-5 recognizes bacterial flagellin. Recently, TLR-9 was identified as the receptor for non-methylated CpG DNA. TLR-3 recognizes double-stranded RNA.
|
TOLL-LIKE RECEPTORS AND ATHEROSCLEROSIS
|
|---|
There is increasing evidence for differential responses in cells activated with different TLR stimuli, indicating that the repertoire of TLRs that detect a pathogen may coordinate a response tailored for defense against a class of organism (Muzio et al., 2000a,b; Visintin et al., 2001). Importantly, recent reports indicate that expression of TLRs is enhanced in atherosclerotic lesions. Dybdahl et al.(2002) reported on the expression of monocyte TLR-2 and TLR-4 following coronary artery bypass grafting in humans. Likewise, Frantz et al.(1999) recently found that cardiac myocytes constitutively express TLR-4, and that this expression is up-regulated in the hearts of humans with cardiovascular disease. TLR-1, TLR-2, and TLR-4 have been reported to be markedly augmented in human atherosclerotic lesions, and expression occurred preferentially by endothelial cells and macrophages (Edfeldt et al., 2002). Another report has demonstrated TLR-2 expression within atherosclerotic plaques in humans (Laman et al., 2002). Xu et al.(2001) recently demonstrated that TLR-4 is expressed in lipid-rich, macrophage-infiltrated atherosclerotic lesions of mice and humans, and that TLR-4 mRNA in cultured macrophages is up-regulated by ox-LDL, but not by native LDL. These findings raise the possibility that enhanced TLR expression may play a role in inflammation in atherosclerosis. Furthermore, the findings of increased expression of TLRs, specifically TLR-4 induced by ox-LDL, suggest a potential mechanism for the synergistic effects of hypercholesterolemia and infection in the acceleration of atherosclerosis observed in experimental models and human epidemiological observations.
A recent study suggests that polymorphisms in the human TLR-4 gene, which attenuates receptor signaling and diminishes the inflammatory response to Gram-negative pathogens, are associated with low levels of certain circulating mediators of inflammation and a decreased risk for atherosclerosis in humans (Kiechl et al., 2002). Likewise, a separate study found that the TLR-4 polymorphism was associated with the risk of cardiovascular events among men with documented coronary artery disease (Boekholdt et al., 2003). Another study reported that this TLR-4 polymorphism does not influence the predisposition for and progression of coronary artery disease (Yang et al., 2003). As discussed by the authors of this study, however, the lack of association does not exclude the involvement of the TLR-4 gene in atherosclerotic plaque formation or plaque stability, as opposed to vessel stenosis. Results from epidemiological studies illustrate how important it is to perform well-controlled animal studies to address the specific involvement of defined innate signaling molecules in the progression of atherosclerosis.
|
ANIMAL MODELS FOR THE STUDY OF ATHEROMA PROGRESSION
|
|---|
Numerous animal models—including those developed for the rat (Herrera et al., 2003), the rabbit (Jain et al., 2003), and mice (Paigen et al., 1987)—have been used for the study of the mechanisms that underlie the progression of atherosclerosis. The studies performed to date include investigation of classically defined risk factors, such as high dietary fat consumption (Lutgens et al., 1999), as well as the impact of innate immune responses in this process (Boring et al., 1998; Collins et al., 2000; Bjorkbacka et al., 2004; Michelsen et al., 2004). The two most widely utilized murine models for the study of atherosclerosis are the apolipoprotein E knockout (ApoE–/–) mice and, to a lesser extent, the low-density lipoprotein receptor knockout (LDLR–/–) mouse (Plump et al., 1992; Ishibashi et al., 1993). Utilization of these animal models for study of the progression of pathogen-accelerated atherosclerosis has been pivotal for the dissection of the mechanisms underlying specific pathogens, the infections they cause, and their effect on the acceleration of atheroma and has been proven useful for several organisms, including P. gingivalis (Epstein et al., 1999b; Moazed et al., 1999; Li et al., 2002; Lalla et al., 2003; Gibson et al., 2004; Spence and Norris, 2003). Additionally, breeding of these genetically hyperlipidemic mice with other defined knockout mice has previously demonstrated functional roles of innate immune molecules in the acceleration of atherosclerosis (Gupta et al., 1997; Bourdillon et al., 2000; Collins et al., 2000; Kirii et al., 2003; Branen et al., 2004), and is an excellent strategy to continue to unravel the mechanisms underlying pathogen-accelerated atherosclerosis.
Emerging animal studies with defined genetic mutants are beginning to demonstrate the importance of TLRs and TLR adapter molecules in the progression of atherosclerosis. Bjorkbacka et al.(2004) reported that MyD88, one of several known adapter molecules for TLR-mediated signal transduction, plays a significant role in atherosclerotic plaque deposition in ApoE-deficient mice. In these studies, MyD88/ApoE double-knockout mice developed ~ 50% less atherosclerotic plaque as compared with ApoE-deficient mice placed on similar high-fat diets (Bjorkbacka et al., 2004). The importance of MyD88 in atherosclerosis was confirmed by Michelsen et al.(2004), and these observations were extended by demonstrations that, in addition to MyD88, TLR4/ApoE double-knockout mice developed significantly less plaque as compared with ApoE-deficient mice. These studies experimentally link the TLR-specific innate immune response (specifically TLR4) and the TLR adapter molecule MyD88 in the progression of atherosclerosis. Future studies will be needed to determine if these observations translate to the progression of atherosclerosis in humans.
|
INFECTION WITH P. gingivalis ACCELERATES ATHEROSCLEROSIS IN AN ApoE MOUSE MODEL
|
|---|
As discussed above, studies performed in humans have recently demonstrated that carotid atheromatous tissue obtained from patients with both periodontal disease and cardiovascular disease possesses P. gingivalis-specific DNA (Haraszthy et al., 2000) and rRNA (Cavrini et al., 2005). These studies suggest that P. gingivalis present in the oral cavity gained access to the vasculature, and that either a bacteremia, or a bacteremia followed by invasion of the vascular endothelium, was responsible for localizing P. gingivalis at this site. These initial studies have been supported by recent studies in an ApoE mouse model of atherosclerosis. Li et al.(2002) initially reported that mice heterozygous at the apoE allele and injected with P. gingivalis via the tail vein were susceptible to accelerated atherosclerosis. Lalla et al.(2003) reported that mice homozygous at ApoE–/–, and were orally challenged with P. gingivalis, were susceptible to accelerated atherosclerosis. Our group has recently demonstrated that only invasive P. gingivalis can accelerate atherosclerosis in the ApoE–/– model (Gibson et al., 2004). In these studies, we observed that ApoE–/–mice challenged with an invasive fimbriate P. gingivalis strain exhibited significantly more atherosclerotic plaque on the intimal surface of the aortic arch, as compared with unchallenged ApoE–/– mice, or with mice challenged with a non-invasive non-fimbriate P. gingivalis mutant (Gibson et al., 2004). Interestingly, we found that oral infection with both the wild-type and the non-invasive mutant resulted in bacteremia and localization in the aortic tissue; however, only the invasive P. gingivalis strain was demonstrated to induce the up-regulation of the innate immune receptors TLR2 and TLR4 (Gibson et al., 2004). Importantly, we also demonstrated that atherosclerosis and innate immune activation are detectable shortly after bacterial infection, and these can be significantly prevented by immunization (Gibson et al., 2004). Taken together, these results indicate that early innate immune activation locally in the aortic arch, in response to infectious challenge, is associated with pathogen-accelerated atherosclerosis and suggest that immunization rather than antibiotic therapy may be required to control pathogen-accelerated atherosclerosis.
|
PUTATIVE MODELS BY WHICH PATHOGENS ACCELERATE ATHEROSCLEROSIS
|
|---|
Results from animal studies linking infection and inflammation to atherosclerosis have enabled investigators to begin to examine putative models for pathogen-accelerated atherosclerosis. While the hypothesis that infection may be associated with atherosclerosis is not novel, having been suggested over 100 years ago by Hektoen (1896), only recently have detailed studies been initiated to test it. To date, four working models have emerged to link mechanisms governing pathogen-accelerated atherosclerosis: (1) direct invasion of the vascular endothelium, (2) immunological sounding, (3) pathogen trafficking, and (4) auto-immunity (Fig. 1 ). It is important to note that one or a combination of these different mechanisms may collectively contribute to pathogen-accelerated atherosclerois.
Direct invasion of and/or replication of a pathogen within endothelial cells has been demonstrated for several organisms, including C. pneumoniae, CMV, and P. gingivalis (Span et al., 1989; Kaukoranta-Tolvanen et al., 1994; Deshpande et al., 1998b) (Fig. 2). Invasion strategies of microbes vary; however, bacterial attachment via fimbriae appears to play a primary role in the subsequent infection of cells, including cells of endothelial origin (Deshpande et al., 1998a). Previously, our group has demonstrated that fimbriae play a central role in the attachment and invasion of endothelial cells by P. gingivalis. Invasive wild-type P. gingivalis readily adhere to and invade endothelial cells (Deshpande et al., 1998b; Progulske-Fox et al., 1999), and invasion stimulates endothelial cells to express elevated levels of cell adhesion molecules and chemokines (Khlgatian et al., 2002; Nassar et al., 2002). Toward this end, a major fimbriae-deficient P. gingivalis mutant (FimA-) failed to adhere to and subsequently invade endothelial cells, and did not elicit cell adhesion molecule or chemokine expression (Khlgatian et al., 2002; Nassar et al., 2002). These results demonstrate that P. gingivalis invasion of endothelial cells is dependent, at least in part, on fimbriae expression, and that endothelial cells challenged with invasive P. gingivalis express markers consistent with activated endothelium present in atheroma. Recently, it has been demonstrated that patients with periodontal disease are at greater risk for developing vascular dysfunction (Amar et al., 2003). Although, in this study, there was no attempt to culture bacteria from atheromatous tissues, when these in vivo observations are combined with in vitro data demonstrating P. gingivalis infection of endothelial cells, it is intriguing to extend these data to suggest that oral pathogens might directly affect vascular endothelium in a manner consistent with increased cardiovascular risk.
View larger version (33K):
[in this window]
[in a new window]
|
Figure 2. Direct invasion of vascular endothelium. (A) In this model, invasion of the vascular endothelium by pathogenic bacteria such as P. gingivalis (red circles) results in the induction of a local inflammatory response, defined by the expression of cell adhesion molecules (CAMs; green trapezoid), Toll-like receptor (TLRs; blue triangle), chemokines, and cytokines. These inflammatory molecules have all demonstrated significant roles in the initiation and/or acceleration of atherosclerosis. The ability of P. gingivalis to stimulate host endothelial cell activation, both in vitro and in vivo, is a function of surface-expressed major fimbriae. P. gingivalis that does not possess fimbriae (fimA) fails to enter endothelial cells efficiently, whereas those organisms that possess fimbriae (wild-type, WT) readily enter these cells (Deshpande et al., 1998b; Khlgatian et al., 2002; Nassar et al., 2002). Following uptake, P. gingivalis-infected endothelial cells, possibly via a receptor-mediated signaling event, activate gene transcription and stimulate these cells to produce a variety of innate immune markers, including CAMs (ICAM-1, VCAM-1), TLRs (TLR-2, TLR-4), pro-inflammatory cytokines (TNF-, IL-1β), and chemokines (MCP-1 and IL-8). These mediators are believed to be involved in the immunological switch of endothelial cells from a normal anti-thrombotic to a pro-thrombotic state. (B) Following P. gingivalis invasion/activation of vascular endothelial cells, these cells recruit monocytes, and, in the presence of elevated circulating lipids such as ox-LDL, atheroma forms.
|
|
The second hypothesis by which pathogens may accelerate atherosclerosis is immunological sounding (Epstein et al., 1999a) (Fig. 3). To the best of our knowledge, there is no direct clinical or experimental evidence linking immunological sounding to the acceleration of atherosclerosis. Thus, this is a hypothetical mechanism by which the inflammatory response to extravascular infection could exacerbate vascular inflammation via secreted cytokines and/or chemokines that ultimately modulate atherosclerosis. In this model, local disease, such as Chlamydia pneumonia, or periodontal disease signals systemic changes in the host inflammatory response via molecules secreted from the site of infection, including acute phase mediators, cytokines, and chemokines. Indeed, it is well-established that atherosclerosis is an inflammatory disease (Ross, 1999), and it is feasible that persistent local infections, such as those in the oral cavity, could promote atherosclerosis via chronic up-regulation of inflammatory cascades (Epstein et al., 1999a). Oral infection with P. gingivalis and the subsequent host response to this organism in the oral cavity are known both to present with inflammatory mediators, as discussed above, and to include C-reactive protein (Noack et al., 2001), IL-1β (Engebretson et al., 2002), TNF- (Roberts et al., 1997), and IL-6 (Geivelis et al., 1993), as well as a vast array of chemokines, including IL-8 (Tsai et al., 1995) and MCP-1 (Hanazawa et al., 1993). Furthermore, with high-fat dietary models of atherosclerotic plaque development/progression in the absence of infection, it has been well-documented that animals deficient in IL-1β (Kirii et al., 2003), INF- (Gupta et al., 1997), and chemokines such as MCP-1 (Gosling et al., 1999) deposit less atherosclerotic plaque compared with wild-type animals.
View larger version (34K):
[in this window]
[in a new window]
|
Figure 3. Infection-induced stimulation of accelerated atherosclerosis by immunological sounding. Persistent local infection, such as oral infections by P. gingivalis, may promote atherosclerosis via chronic up-regulation of inflammatory cascades involving TNF-, IL-1, IFN, IL-8, MCP-1, and CRP. These cytokines, chemokines, and acute phase mediators could be shed into the vasculature from a focus of P. gingivalis infection in the periodontium. Once in the circulation, these mediators may subsequently activate vascular endothelial cells in a manner that shifts them from a normally anti-thrombotic state to one expressing high levels of inflammatory mediators, including CAMs (blue triangles) and TLRs (green trapezoid), that become pro-thrombotic. This activated endothelium would likely be a site for subsequent atheroma formation, independent of direct pathogen involvement at this site. This further immunological activation results in the recruitment of monocytes, as well as the stimulation, migration, and proliferation of smooth-muscle cells that, together with elevated levels of circulating lipids such as ox-LDL, ultimately results in acceleration of the atheroma.
|
|
Chronic local infections such as periodontitis, despite evidence of a specific inflammatory response to clear the pathogen, are not readily cleared by the host. Thus, perpetuation of these infections may result in low-level, long-term, "smoldering" immunological activation that could result in chronically stimulated cytokine and chemokine production. Since it is known that cytokines and chemokines play a role in the activation of endothelium, SMCs, and the monocytes associated with developing atheroma (Ross, 1999), it is feasible that chronic periodontal infections generate an environment, in the aorta and arterial vasculature, conducive to atheroma development via soluble mediators secreted into the circulation from the oral cavity. The activation of vascular endothelium in response to inflammatory cytokines and chemokines would shift the balance of the vascular endothelium from a "healthy", normal, anti-thrombotic environment to a "diseased", pro-thrombotic environment (Vita and Loscalzo, 2002), and would up-regulate cell adhesion molecule expression that could subsequently participate in the localization of leukocytes (Springer, 1990). To this end, it has been demonstrated, by several groups, that endothelial cells cultured with P. gingivalis, or P. gingivalis outer membrane vesicles, express cell adhesion molecules that could play a role in the establishment and/or acceleration of atheroma (Srisatjaluk et al., 1999; Khlgatian et al., 2002).
In addition to the localization of inflammatory cells to activated endothelium expressing cell adhesion molecules, endothelium could perpetuate the inflammatory lesion by production of soluble mediators that could further stimulate both the migration and proliferation of SMCs (Libby, 2002). Indeed, we previously reported that HUVEC cells cultured with P. gingivalis produced IL-8 and MCP-1 (Nassar et al., 2002). Moreover, it was demonstrated, in that study, that production of these chemokines by HUVEC was dependent on fimbriate organisms, since a P. gingivalis fimA mutant failed to induce chemokine production from HUVEC (Nassar et al., 2002). In addition, Khlgatian et al.(2002) demonstrated that HUVEC cultured with wild-type P. gingivalis, but not a fimA-deficient mutant, elicited surface expression of selectins, ICAM-1, and VCAM-1.
To date, it has not been demonstrated experimentally that immunological sounding from an extravascular infection is a mechanism by which local infection can aggravate systemic diseases such as atherosclerosis. Despite this, intranasal challenge of mice with Chlamydia (Hu et al., 1999), as well as oral challenge of mice with P. gingivalis (Lalla et al., 2003), as discussed above, present with evidence of local infection and aggravation of atherosclerosis. In each of these studies, there was evidence of pathogen localization in the site pre-disposed for atheroma development, thereby failing to support immunological sounding; however, cultivation of organisms from these sites has remained elusive. Analysis of these data supports the hypothesis that infection-accelerated atherosclerosis may be limited to those pathogens which gain access to the vasculature, interact with vascular endothelium, and activate these cells in a manner that accelerates atheroma deposition.
Although the data have many interpretations, it could be argued that inflammatory mediators, released at the site of local infection, initiate the activation of vascular endothelium, and then microbial antigens or DNA released from these pathogens could reach the circulation and bind to endothelial cells or localize with the developing atheroma. In culture, some strains of P. gingivalis produce vesicles (Srisatjaluk et al., 1999), and these vesicles might be released into the circulation, thus serving as a source of P. gingivalis antigens. Thus, it is reasonable to consider that chronic shedding of bacterial components into the vasculature may be capable of accelerating atherosclerosis. Human studies suggest that, shortly after dental treatment, P. gingivalis bacteremia is evident (Messini et al., 1999), and analysis of recent data from the study of mice suggests that P. gingivalis enters the vasculature soon after oral challenge (Gibson et al., 2004). It is feasible that, upon entering this immunologically privileged site, the host mounts a response to this organism while it is in the blood, independent of pathogen-endothelium interactions. It is well-documented that both monocytes and PMNs are activated and secrete pro-inflammatory cytokines and chemokines when cultured with P. gingivalis (Ishikawa et al., 1997; Landi et al., 1997). Thus, the immunological response to blood-borne infection may be sufficient to activate the host immunologically in a manner that promotes atherosclerosis. Future studies are needed to determine the impact of chronic local infection, the inflammatory response to these infections, and its relationship with the acceleration of atherosclerosis.
Conceptually similar to the second model, the third model for assessing the role of infection as a risk factor for pathogen-accelerated atherosclerosis is via trafficking of pathogens from the local site of infection (such as the oral cavity) to the developing atheroma via inflammatory cells (Fig. 4). In this model, as a result of the tissue damage caused by the infection and subsequent inflammatory response, the inflammatory cells present at the local infection ingest the pathogens, and, upon re-emergence of these pathogen-laden inflammatory cells into the vasculature, subsequent localization at the site of developing atheroma may occur. There is a paucity of experimental data to support the hypothesis that pathogen trafficking is valid for the study of atherosclerosis development; however, in other diseases, transport of an infectious agent inside an inflammatory cell from one anatomical site to another has been reported. HIV infection of macrophages has been suggested to be an important mechanism in facilitating HIV infection of the CNS, presumably via HIV infection of monocytes and/or lymphocytes, followed by subsequent trans-endothelial cell migration through the blood-brain barriers (Nottet et al., 1996). MacIntyre et al.(2003) reported that C. pneumoniae infection of THP-1 monocytes up-regulated trans-endothelial migration of the infected cells through human brain endothelial cells by as much as three-fold over that observed for uninfected cells. Additionally, it has been demonstrated that Listeria monocytogenes can efficiently spread from macrophages to endothelial cells when these host cells are in proximity (Greiffenberg et al., 1998). Although these examples do not directly link pathogen trafficking to the vascular endothelium, and thus the site of atheroma development, these studies suggest that a variety of organisms, including those associated with increased risk for cardiovascular disease development, are capable of facilitating increased activity between mononuclear cells and endothelium. In contrast to facilitating host cell interactions and pathogen trafficking, Madianos et al.(1997), using a transwell cell migration system, demonstrated that oral epithelial cells infected with P. gingivalis were inhibited in allowing PMN trans-epithelial cell migration. Further studies with endothelial cells and mononuclear cells will be needed in this area for the determination of how P. gingivalis infection affects cell-cell interactions and the impact of these interactions on subsequent atheroma development.
View larger version (35K):
[in this window]
[in a new window]
|
Figure 4. Trafficking of pathogens. Localization of pathogens to the endothelium may occur via host immune cells. Oral infection by pathogens such as P. gingivalis leads to considerable tissue damage and stimulates a complex cellular inflammatory lesion that partly characterizes periodontitis. Phagocytic mononuclear cells such as macrophages are responsible for clearance of non-self antigens via phagocytosis and can ingest P. gingivalis at the site of infection in the oral cavity. Upon phagocytosis, it may be possible for some pathogens to resist phagocytic killing and persist within these cells. Without a chemokine gradient to localize to the site of infection, due either to P. gingivalis cysteine protease (gingipain)-mediated cleavage of inflammatory mediators, or to infection-elicited localized chemokine paralysis, infected phagocytes could leave the site of infection and emigrate back to the circulation. These circulating infected macrophages could then interact with immunologically activated endothelial cells at the site of a developing atheroma, first by localizing via a chemotactic gradient (IL-8 and MCP-1), followed by tight adherence to the endothelium via CAMs (green trapezoid). At this point, bacterial antigens or viable bacteria could be released from these cells, and, ultimately, together with elevated levels of circulating lipids such as ox-LDL, result in acceleration of atherosclerosis.
|
|
The final hypothesis we will discuss here by which infectious agents accelerate atherosclerosis is by stimulation of an auto-immune response via molecular mimicry (Wick et al., 1995; Epstein et al., 1999a; Libby et al., 2002). Molecular mimicry requires infection by a pathogen that possesses molecules with significant homology to a host structure (Fig. 5). The host response is initiated against the pathogen; however, the response then presents as an auto-immune insult against those host tissues that possess these cross-reactive epitopes (Wick et al., 1995). At the site of infection, elevated levels of cytokines, free radicals, homocysteine, hypercholesterolemia, hypertension, and, potentially, destruction of both endothelial cells and infiltrating phagocytic cells and the infectious agent would become a focus for elevated pathogen-specific and host-specific HSP release. In combination with these aforementioned factors, both host and pathogen HSPs would be responsible for generating a site of immunologic activity that would lead to subsequent immunologic activation, and thus facilitate the progression of atherosclerosis via an auto-immune response (Epstein et al., 1999a; Xu, 2003). The best-described mechanism of molecular mimicry in pathogen-accelerated atherosclerosis is that for heat-shock proteins (HSPs). HSPs are evolutionarily conserved molecules, and both bacterial and human HSPs possess a high degree of sequence and structural homology (Lamb et al., 2003). Furthermore, it has been reported that serologic cross-reactivity exists between human HSPs and both Chlamydia and M. tuberculosis HSPs (Barrios et al., 1994; Xu, 2003). Interestingly, it was reported that patients with cardiovascular disease presented with elevated levels of cross-reactive antibody that recognized both Chlamydia HSP and human HSP (Xu, 2003). More recently, Chung et al.(2003) have reported that patients with atherosclerosis and periodontal disease possess antibodies that react with P. gingivalis HSPs. In a continuation of this line of experimentation, Yamazaki et al.(2004) reported elevated serum antibody levels to P. gingivalis HSP60 (GroEL) and human HSP60 in patients with atherosclerosis, as well as patients with periodontal disease. There were the added observations in this work that T-cells were detected in human atheroma from these patients, and that these cells responded to P. gingivalis GroEL and human HSP60 (Yamazaki et al., 2004). Analysis of these data supports cross-reactivity between P. gingivalis and host antigens, and suggests the auto-immune response hypothesis as a plausible mechanism for P. gingivalis-acceleration of atherosclerosis.
View larger version (25K):
[in this window]
[in a new window]
|
Figure 5. Infection-induced stimulation of accelerated atherosclerosis by molecular mimicry. Molecular mimicry requires infection by a pathogen that possesses a molecule with significant homology to a host molecule. Following a host response initiated to this molecule, the response then presents as an auto-immune insult against those tissues with cross-reactive epitopes. Depicted here, conserved proteins such as bacterial HSPs (pink diamonds) and host HSPs (pink diamonds with cross) are exposed as a result of tissue damage and the host response to infection. Specific antibody directed toward bacterial HSPs would cross-react with human HSPs, setting in motion a localized auto-immune response. Indeed, cross-reactive antibodies to bacterial and host HSPs have been reported. The resulting inflammatory response could lead to endothelial cell damage, and ultimately, together with monocyte recruitment and the presence of elevated circulating lipids such as ox-LDL, to the acceleration of the atheroma.
|
|
In addition to HSP, other molecules that share homology between pathogens associated with atherosclerosis and host proteins include IL-6, IL-10, and chemokine receptors (Spriggs, 1996; Epstein et al., 1999a). The impacts of these other molecules, which may represent sites of antigenic cross-reactivity with bacterial structures, are poorly understood and will not be discussed here. Thus, several classes of molecules present on pathogens may "resemble" host molecules associated with inflamed areas of the vasculature or developing atherosclerotic lesions, indicating that molecular mimicry may be an important mechanism that underlies pathogen-accelerated atherosclerosis. Analysis of recent animal data has begun to validate this hypothesis, and supports the theory that injection of HSP into hyperlipidemic mice aggravates atheroma development (Afek et al., 2000); however, direct evidence that this response is in fact via molecular mimicry has not been confirmed in humans. Future studies will likely shed light on this important area of study regarding the mechanisms of infection-accelerated atherosclerosis.
|
In vitro STUDIES SUPPORT THAT INVASIVE P. gingivalis ACTIVATES THE INNATE IMMUNE RESPONSES OF HOST CELLS IN A MANNER PARALLELING THAT OBSERVED DURING THE DEVELOPMENT OF ATHEROSCLEROSIS
|
|---|
Endothelial Cells
Previously, our group and others have reported that endothelial cells challenged with invasive P. gingivalis are susceptible to infection, and these cells respond vigorously to challenge by up-regulating many aspects of their innate immune response armamentarium, including cell adhesion molecules, selectins, chemokines, and TLRs (Khlgatian et al., 2002; Nassar et al., 2002; Yumoto, unpublished observations). Since it has been reported that endothelial cells obtained from various anatomical sites possess variable responsiveness to stimulation (Morris et al., 1993; Ikeda et al., 1999), studies have been initiated to develop a better understanding of the responsiveness of arterial vessel endothelial cells to P. gingivalis. Primary cultures of human aortic endothelial cells (HAEC; Yumoto, unpublished observations), as well as human coronary artery endothelial cells (HCAEC; Progulske-Fox et al., 1999), have demonstrated levels of susceptibility to invasive P. gingivalis infection similar to those reported with HUVEC cells. Moreover, the role of fimbriae-mediated attachment to aortic endothelial cells may mimic those observations previously reported for HUVEC cells (Khlgatian et al., 2002).
To identify whether aortic endothelial cells are stimulated in a manner that could facilitate inflammatory cell migration to these cells, and subsequently support firm attachment to these cells (an important step in the initial development of atherosclerotic lesion formation), we cultured human aortic endothelial cells with P. gingivalis and assessed the inflammatory responses of these cells, including cell adhesion molecule expression, TLR regulation, and chemokine expression. Assessment of ICAM-1, VCAM-1, and selectin expression in response to wild-type P. gingivalis revealed that HAEC cultured with live, fimbriate P. gingivalis produced high levels of these markers (Takahashi et al., manuscript under review). Interestingly, HAEC cultured with a fimA- P. gingivalis mutant failed to stimulate ICAM-1, VCAM-1, and selectin expression. These data are in agreement with those from our previous studies demonstrating that wild-type P. gingivalis, but not a fimA-deficient mutant, accelerated atherosclerotic plaque deposition in an ApoE–/– mouse model (Gibson et al., 2004). Furthermore, we observed that HAECs cultured with the purified FimA protein were also stimulated to express ICAM-1, VCAM-1, and selectin on their surfaces (Takahashi et al., manuscript under review). Analysis of these data demonstrates a central role for fimbriae in vascular endothelial cell activation in response to P. gingivalis, since FimA-deficient organisms fail to elicit CAM expression on HAECs, and that purified protein is sufficient to activate a CAM response from these cells.
Since TLRs have been detected in human atherosclerotic lesions, we have been interested in endothelial cell TLR regulation in response to P. gingivalis challenge. Previously, we reported that TLR2 and TLR4 were up-regulated on the surfaces of HAECs challenged with wild-type P. gingivalis, but not a fimA- mutant (Gibson et al., 2004). Interestingly, the TLR expression profile when we cultured HAECs with purified FimA protein differed from that observed with CAM expression. HAECs cultured with FimA failed to regulate TLR2 or TLR4 expression (Gibson et al., 2004; Yumoto, unpublished observations). This was not the case with CAM expression in response to the FimA protein, since we observed that CAMS were up-regulated in response to purified FimA. Analysis of these data suggests that different mechanisms and signaling pathways are responsible for CAM and TLR regulation on vascular endothelium in response to microbial challenge. Further studies in this area will likely yield important data that may further implicate the TLR innate immune response to select sets of pathogens and development of pathogen-accelerated atherosclerosis.
To define further the interactions of P. gingivalis with endothelial cells, we cultured monolayers of HAECs with various multiplicities of infection (MOI) of P. gingivalis and a P. gingivalis fimA- mutant, and assessed chemokine expression from HAEC. We observed that, at an MOI of 100, P. gingivalis elicited a potent IL-8 and MCP-1 response from HAEC, while at an MOI of 500, we detected lower levels of these inflammatory mediators (Figs. 6, 7). The apparent discrepancy in the dose-dependent expression of chemokine expression from HAECs challenged with the higher dose of P. gingivalis may be related to the production of gingipains, since it has been demonstrated that gingipains can cleave a variety of inflammatory mediators, including TNF- (Calkins et al., 1998) and IL-6 (Banbula et al., 1999). Importantly, we observed that HAECs cultured with the P. gingivalis fimA mutant produced significantly less IL-8 and MCP-1 than HAECs cultured with wild-type P. gingivalis, and resembled levels produced by HAEC cultured in medium alone (Figs. 6, 7). Analysis of these data supports the hypothesis that fimbriae-dependent mechanisms play a role in endothelial cell chemokine expression in response to P. gingivalis. Future studies of purified P. gingivalis surface-expressed proteins (such as FimA) and LPS will likely provide important information regarding the impact of P. gingivalis structures and attachment/invasion strategies in the P. gingivalis acceleration of atherosclerosis.
View larger version (19K):
[in this window]
[in a new window]
|
Figure 6. MCP-1 expression in HAEC, monocytes, and HAEC/monocyte co-cultures. P. gingivalis 381 (wt) or the fimA mutant DPG3 (fimA) was used to infect HAEC (A) human monocytes or (B) HAEC/human monocyte co-cultures (C) at an MOI of 1:100 (100) or 1:500 (500), and MCP-1 was measured by ELISA after 24 hrs. Uninfected HAEC, monocytes, and HAEC/monocyte co-cultures (control) served as negative controls. Analysis of these data demonstrates that cultures of primary HAEC, human peripheral blood monocytes, and HAEC/monocyte co-cultures actively respond to P. gingivalis challenge. Moreover, the MCP-1 response observed in the co-culture system is not simply additive, but rather, some unknown interaction occurs between endothelial cells and macrophages during P. gingivalis challenge, giving rise to a synergistic response.
|
|
View larger version (18K):
[in this window]
[in a new window]
|
Figure 7. IL-8 expression in HAEC, monocytes, and HAEC/monocyte co-cultures. P. gingivalis 381 (wt) or the fimA mutant DPG3 (fimA) was used to infect HAEC (A), human monocytes (B), or HAEC/human monocyte co-cultures (C) at an MOI of 1:100 (100) or 1:500 (500), and IL-8 was measured by ELISA after 24 hrs. Uninfected HAEC, monocytes, and HAEC/monocyte co-cultures (control) served as negative controls. Analysis of these data demonstrates that cultures of primary HAEC, human peripheral blood plastic adherent monocytes, and HAEC/monocyte co-cultures actively respond to P. gingivalis challenge. The IL-8 response observed in these systems parallels that observed for MCP-1 (Fig. 6 ). The co-culture system supports that some unknown interaction between endothelial cells and macrophages during P. gingivalis challenge is likely occurring, giving rise to a synergistic response.
|
|
Monocytes
The macrophage is one of the hallmark cells of both chronic periodontitis and atherosclerosis. This cell plays a pivotal role in the clearance of infectious agents; however, the specific role of macrophages in controlling P. gingivalis oral infection is poorly understood. Furthermore, macrophages laden with lipid (called ’foam cells’) localize to sites of activated endothelium and comprise the primary cell of the fatty streak, the first pathological evidence of a developing atherosclerotic lesion (Stary et al., 1994).
Chemokine production is essential for activating and localizing effecter cells to a site of infection, and MCP-1 and IL-8 have been reported to play important roles in the development of atherosclerosis (Koch et al., 1993; Reape and Groot, 1999; Ito and Ikeda, 2003). Since endothelial cells produce IL-8 in response to invasive P. gingivalis (Nassar et al., 2002), we were interested to determine whether the invasive P. gingivalis phenotype played a role in macrophage chemokine expression. Human plastic adherent peripheral blood monocytes were cultured in medium, wild-type P. gingivalis 381, or the fimA mutant at MOIs of 100 and 500. We observed that these monocytes elicited a more robust IL-8 response to P. gingivalis compared with endothelial cells. Invasive P. gingivalis at an MOI of 100 elicited a very strong IL-8 response (Figs. 6, 7). Interestingly, at an MOI of 500, the detected level of IL-8 in the culture supernatant fluids was less than that observed with an MOI of 100. As discussed above, this may be due to the production of gingipains, which can degrade IL-8 secreted in these supernatant fluids. The fimA mutant elicited significantly less IL-8 as compared with wild-type P. gingivalis; however, these levels were greater than that observed by medium challenge alone. Analysis of these data supports the hypothesis that fimbriate P. gingivalis stimulate monocytes to produce chemokines that may signal the recruitment of inflammatory cells to the site of P. gingivalis infection (Fig. 6, 7).
Based on these data, we have developed a model to simplify our observations of the interactions of P. gingivalis with macrophages (Fig. 8). First, it is apparent that live, invasive P. gingivalis is required for adherence to and invasion of macrophages, since a fimA mutant failed to invade these cells. It has been proposed that microbial PAMPS are responsible for innate immune recognition of infection. This also appears to be the case for P. gingivalis. Other investigators, as well as our studies, support the role of TLR-signaling in cell activation. The transcriptiome of monocytes during P. gingivalis challenge is not known; however, analysis of our data supports the hypothesis that monocytes in the presence of invasive P. gingivalis rapidly regulate the expression of TLRs on the surfaces of these cells (Yumoto, unpublished observations). In conjunction with these observations, monocytes challenged with invasive P. gingivalis produce chemokines, molecules that are critical to the recruitment of inflammatory cells to the site of P. gingivalis infection. Further studies are required to determine the nature of the interaction of P. gingivalis with macrophages. Nonetheless, analysis of our data supports the hypothesis that P. gingivalis elicits an innate immune response from human monocytes that is consistent with that observed during the development of atherosclerosis.
View larger version (33K):
[in this window]
[in a new window]
|
Figure 8. Model of the interactions of P. gingivalis with host cells. Invasive P. gingivalis can interact with both the aortic endothelium (A) and monocytes (B), and can initiate a potent innate immune response. The combination of the endothelium and the monocytes (C) is more responsive to P. gingivalis than either of the individual cell types alone. In all cases, cells infected with wild-type P. gingivalis (WT; left of dashed line) elicit a more potent response than the major fimbriae-deficient P. gingivalis (FimA-; right of dashed line). Size of arrow indicates relative magnitude of the host response.
|
|
Endothelial Cell/Monocyte Co-cultures
The development of atherosclerosis is a multi-factorial process that involves several host cell types. One of the earliest cellular interactions that must occur for incipient atherosclerotic plaque deposition is the localization of monocytes or macrophages to inflamed vascular endothelium at the site of the developing atheroma. We hypothesized that co-cultures of monocytes and vascular endothelium challenged with P. gingivalis would result in a host response profile that was different from that observed with the individual host cells challenged with P. gingivalis (Fig. 8). To address this, we cultured human plastic adherent peripheral blood monocytes with monolayers of endothelial cells at a ratio of 1:1, and assessed supernatant fluid levels of IL-8. Interestingly, when monocytes were placed in culture with endothelial cells and challenged with P. gingivalis, we observed an IL-8 response that was greater than the additive effect of endothelial cell and monocytes (Figs. 6, 7). This response to P. gingivalis was dependent on fimbriae, since the P. gingivalis fimA mutant elicited less IL-8 as compared with wild-type P. gingivalis. We also noted that, at a high MOI, IL-8 levels were reduced compared with those observed with a low MOI, and this may reflect gingipain-mediated cleavage of IL-8. As indicated in our model (Fig. 8), the invasive P. gingivalis phenotype is necessary for potent innate immune responses by both monocytes and endothelial cells. Furthermore, using a complex cell culture system, we observed that endothelial cell/monocyte co-cultures are more responsive to P. gingivalis than either of the individual cell types alone. Continued studies in this area will determine if this observed innate immune response synergy to P. gingivalis is dependent on direct monocyte/endothelial cell contact, or the result of communication between the two cell types via soluble mediators, such as cytokines and chemokines.
|
P. gingivalis STIMULATION OF CELL SIGNALING IS MEDIATED IN PART BY TLRs
|
|---|
The innate immune signaling via the TLRs in response to P. gingivalis infection is poorly understood. Moreover, the specific pathways that are engaged during P. gingivalis infection of various host cells are equally poorly defined. The two best-described antigens that have been investigated regarding TLR-mediated signaling are LPS and fimbriae. While P. gingivalis LPS activation through TLR2 has been established, the activation pathway for other P. gingivalis fimbriae or live bacteria has not. A study with human gingival epithelial cells, which predominantly expressed TLR2 but not TLR4 or CD14, suggests that P. gingivalis fimbriae signal through TLR2 (Asai et al., 2001). However, since these cells do not express TLR4, it cannot be concluded that P. gingivalis use only TLR2 for activation. A separate study with THP-1 mononuclear cells suggests that the CD14-TLR2/4 system is involved in cytokine production and tolerance induction upon interaction with P. gingivalis fimbriae (Hajishengallis et al., 2002). Extensive investigation of this area will undoubtedly yield interesting data that will further define the role of these and other P. gingivalis structures involved in innate immune signaling to this organism, and the potential impact of these responses in infection-accelerated atherosclerosis.
|
MONOCYTES AND MACROPHAGES CULTURED WITH P. gingivalis FORM FOAM CELLS
|
|---|
The earliest pathological lesion of developing atheroma in arterial vessels is the fatty streak (Stary et al., 1994). This lesion is comprised mostly of macrophages engorged with lipid, termed ’foam cells’ (Stary et al., 1994). Microbe-elicited macrophage conversion to foam cells has been reported for a variety of cells cultured with C. pneumoniae (Kalayoglu and Byrne, 1998). More recent studies support the hypothesis that monocytes or macrophages obtained from various sources, stimulated with P. gingivalis, are more prone to develop into foam cells when cultured in medium supplemented with high levels of low-density lipoproteins, compared with similar cells cultured in LDL-supplemented medium alone (Kuramitsu et al., 2001; Qi et al., 2003; Giacona et al., 2004) (Fig. 9). Interestingly, mutational analysis of the contribution of P. gingivalis adherence to macrophages as a predisposing event in foam cell stimulation has revealed that FimA-deficient P. gingivalis fails to stimulate foam cell formation (Giacona et al., 2004). Studies by Miyakawa et al.(2004) indicate that, in addition to P. gingivalis attachment to macrophages, gingipains may contribute to foam cell formation, either directly by activating cells, or by modification of LDL. Since analysis of our data supports the hypothesis that endothelium/monocyte co-cultures challenged with P. gingivalis are more active producers of chemokines than either cell challenged with P. gingivalis alone, it would be interesting to determine if the endothelium/monocyte interaction influences P. gingivalis foam cell formation. Future studies into the mechanisms underlying P. gingivalis-elicited foam cell formation may provide fruitful information regarding pathogen stimulation of atherosclerosis.
View larger version (26K):
[in this window]
[in a new window]
|
Figure 9. Stimulation of mononuclear cells to form foam cells. Infection of mononuclear cells by bacterial pathogens sets in motion a series of events that lead to monocyte activation. Several pathogens epidemiologically linked to the acceleration of atherosclerosis have demonstrated the ability to elicit macrophages to form into foam cells—lipid-laden cells that possess a foamy appearance due to lipid accumulation and are the cells characteristic of an early-stage atheroma called the fatty streak. Recent studies have demonstrated that P. gingivalis stimulates macrophage foam cell formation, and this process appears to be dependent on the attachment of this organism to the macrophage. As part of the characteristic host response of macrophages to infection, these cells express elevated levels of CAMs (green trapezoid) that increase the adhesiveness of these cells to endothelial cells. Additionally, these cells express elevated levels of cytokines and chemokines, as well as TLRs (blue triangles), that could increase macrophage localization to the site of this infected macrophage, as well as increase the sensitivity of these macrophages to specific PAMPs. Ultimately, these mononuclear cells could go on to develop into foam cells as a result of the uptake of serum lipids, including ox-LDL.
|
|
|
CONCLUSIONS
|
|---|
It is evident that ~ 50% of patients with cardiovascular conditions do not possess any of the classic risk factors, such as high-circulating cholesterol, smoking, exercise, and genetics; thus, additional risk factors that predispose to atherosclerosis remain. Atherosclerosis is an inflammatory disease, and both innate and adaptive immune responses are believed to play a role in atheroma progression. Many parallels exist between host responses during atherosclerosis and infection. Recently, the role of TLRs in atherosclerosis has been investigated. The concept that infections can accelerate atherosclerosis are controversial; however, epidemiological and experimental studies support the hypothesis that certain specific chronic infections, such as periodontal disease, may be associated with pathogen-accelerated atherosclerosis and cardiovascular disease. Recent studies have established that infection with the periodontal disease pathogen P. gingivalis can accelerate atherosclerosis in an ApoE–/– mouse model of disease (Li et al., 2002; Lalla et al., 2003). Studies from our laboratory have established that this process is specific and dependent on an invasive pathogen phenotype, and that we can prevent pathogen-accelerated atherosclerosis by immunization (Gibson et al., 2004). Furthermore, analysis of our data supports a pivotal role for TLRs in infection-accelerated atherosclerosis. Emerging data from our laboratory have demonstrated that P. gingivalis invades endothelial cells, and that invasive P. gingivalis elicits TLR2 and TLR4 expression on endothelial cells as well as chemokines and cell adhesion molecules. It is compelling to consider that the innate immune inflammatory response elicited by P. gingivalis, or other pathogens associated with increased risk for atherosclerosis, could be one of the early events in establishing a potential focus for the development of atherosclerosis. Continued investigations should focus on the mechanistic links among TLRs, infection, and atherosclerosis.
|
ACKNOWLEDGMENTS
|
|---|
The authors are supported by Public Health Service grants PO1DE13191 (C.A.G.) and R01DE14774 (F.C.G.) from the National Institute of Dental and Craniofacial Research.
Received for publication January 18, 2005.
Accepted for publication June 20, 2005.
|
REFERENCES
|
|---|
- Afek A, George J, Gilburd B, Rauova L, Goldberg I, Kopolovic J, et al. (2000). Immunization of low-density lipoprotein receptor deficient (LDL-RD) mice with heat shock protein 65 (HSP-65) promotes early atherosclerosis. J Autoimmun 14:115–121.[CrossRef][Medline]
[Order article via Infotrieve]
- Amar S, Gokce N, Morgan S, Loukideli M, Van Dyke TE, Vita JA (2003). Periodontal disease is associated with brachial artery endothelial dysfunction and systemic inflammation. Arterioscler Thromb Vasc Biol 23:1245–1249.[Abstract/Free Full Text]
- Asai Y, Ohyama Y, Gen K, Ogawa T (2001). Bacterial fimbriae and their peptides activate human gingival epithelial cells through Toll-like receptor 2. Infect Immun 69:7387–7395.[Abstract/Free Full Text]
- Bainbridge BW, Darveau RP (2001). Porphyromonas gingivalis lipopolysaccharide: an unusual pattern recognition receptor ligand for the innate host defense system. Acta Odontol Scand 59:131–138.[CrossRef][Medline]
[Order article via Infotrieve]
- Banbula A, Bugno M, Kuster A, Heinrich PC, Travis J, Potempa J (1999). Rapid and efficient inactivation of IL-6 gingipains, lysine- and arginine-specific proteinases from Porphyromonas gingivalis. Biochem Biophys Res Commun 261:598–602.[CrossRef][Medline]
[Order article via Infotrieve]
- Barrios C, Tougne C, Polla BS, Lambert PH, Del Giudice G (1994). Specificity of antibodies induced after immunization of mice with the mycobacterial heat shock protein of 65 kD. Clin Exp Immunol 98:224–228.[Medline]
[Order article via Infotrieve]
- Beck J, Garcia R, Heiss G, Vokonas PS, Offenbacher S (1996). Periodontal disease and cardiovascular disease. J Periodontol 67(10 Suppl):1123–1137.[Medline]
[Order article via Infotrieve]
- Beck JD, Offenbacher S, Williams R, Gibbs P, Garcia R (1998). Periodontitis: a risk factor for coronary heart disease? Ann Periodontol 3:127–141.[Medline]
[Order article via Infotrieve]
- Beutler B (2002). Toll-like receptors: how they work and what they do. Curr Opin Hematol 9:2–10.[CrossRef][Medline]
[Order article via Infotrieve]
- Bjorkbacka H, Kunjathoor VV, Moore KJ, Koehn S, Ordija CM, Lee MA, et al. (2004). Reduced atherosclerosis in MyD88-null mice links elevated serum cholesterol levels to activation of innate immunity signaling pathways. Nat Med 10:416–421.[CrossRef][Medline]
[Order article via Infotrieve]
- Blum A, Giladi M, Weinberg M, Kaplan G, Pasternack H, Laniado S, et al. (1998). High anti-cytomegalovirus (CMV) IgG antibody titer is associated with coronary artery disease and may predict post-coronary balloon angioplasty restenosis. Am J Cardiol 81:866–868.[CrossRef][Medline]
[Order article via Infotrieve]
- Boekholdt SM, Agema WR, Peters RJ, Zwinderman AH, van der Wall EE, Reitsma PH, et al. (2003). Variants of toll-like receptor 4 modify the efficacy of statin therapy and the risk of cardiovascular events. Circulation 107:2416–2421.[Abstract/Free Full Text]
- Boring L, Gosling J, Cleary M, Charo IF (1998). Decreased lesion formation in CCR2–/– mice reveals a role for chemokines in the initiation of atherosclerosis. Nature 394:894–897.[CrossRef][Medline]
[Order article via Infotrieve]
- Bourdillon MC, Poston RN, Covacho C, Chignier E, Bricca G, McGregor JL (2000). ICAM-1 deficiency reduces atherosclerotic lesions in double-knockout mice (ApoE(–/–)/ICAM-1(–/–)) fed a fat or a chow diet. Arterioscler Thromb Vasc Biol 20:2630–2635.[Abstract/Free Full Text]
- Branen L, Hovgaard L, Nitulescu M, Bengtsson E, Nilsson J, Jovinge S (2004). Inhibition of tumor necrosis factor-alpha reduces atherosclerosis in apolipoprotein E knockout mice. Arterioscler Thromb Vasc Biol 24:2137–2142.[Abstract/Free Full Text]
- Calkins CC, Platt K, Potempa J, Travis J (1998). Inactivation of tumor necrosis factor-alpha by proteinases (gingipains) from the periodontal pathogen, Porphyromonas gingivalis. Implications of immune evasion. J Biol Chem 273:6611–6614.[Abstract/Free Full Text]
- Cavrini F, Sambri V, Moter A, Servidio D, Marangoni A, Montebugnoli L, et al. (2005). Molecular detection of Treponema denticola and Porphyromonas gingivalis in carotid and aortic atheromatous plaques by FISH: report of two cases. J Med Microbiol 54:93–96.[Abstract/Free Full Text]
- Chung SW, Kang HS, Park HR, Kim SJ, Choi JI (2003). Immune responses to heat shock protein in Porphyromonas gingivalis-infected periodontitis and atherosclerosis patients. J Periodontal Res 38:388–393.[Medline]
[Order article via Infotrieve]
- Collins RG, Velji R, Guevara NV, Hicks MJ, Chan L, Beaudet AL (2000). P-selectin or intercellular adhesion molecule (ICAM)-1 deficiency substantially protects against atherosclerosis in apolipoprotein E-deficient mice. J Exp Med 191:189–194.[Abstract/Free Full Text]
- D’Aiuto F, Ready D, Tonetti MS (2004). Periodontal disease and C-reactive protein-associated cardiovascular risk. J Periodontal Res 39:236–241.[CrossRef][Medline]
[Order article via Infotrieve]
- Darveau RP, Belton CM, Reife RA, Lamont RJ (1998). Local chemokine paralysis, a novel pathogenic mechanism for Porphyromonas gingivalis. Infect Immun 66:1660–1665.[Abstract/Free Full Text]
- Dasanayake AP, Russell S, Boyd D, Madianos PN, Forster T, Hill E (2003). Preterm low birth weight and periodontal disease among African Americans. Dent Clin North Am 47:115–125, x–xi.[CrossRef][Medline]
[Order article via Infotrieve]
- Deshpande RG, Khan M, Genco CA (1998a). Invasion strategies of the oral pathogen Porphyromonas gingivalis: implications for cardiovascular disease. Invasion Metastasis 18:57–69.
- Deshpande RG, Khan MB, Genco CA (1998b). Invasion of aortic and heart endothelial cells by Porphyromonas gingivalis. Infect Immun 66:5337–5343.[Abstract/Free Full Text]
- Dybdahl B, Wahba A, Lien E, Flo TH, Waage A, Qureshi N, et al. (2002). Inflammatory response after open heart surgery: release of heat-shock protein 70 and signaling through toll-like receptor-4. Circulation 105:685–690.[Abstract/Free Full Text]
- Edfeldt K, Swedenborg J, Hansson GK, Yan ZQ (2002). Expression of toll-like receptors in human atherosclerotic lesions: a possible pathway for plaque activation. Circulation 105:1158–1161.[Abstract/Free Full Text]
- Engebretson SP, Grbic JT, Singer R, Lamster IB (2002). GCF IL-1beta profiles in periodontal disease. J Clin Periodontol 29:48–53.[CrossRef][Medline]
[Order article via Infotrieve]
- Epstein SE, Zhou YF, Zhu J (1999a). Infection and atherosclerosis: emerging mechanistic paradigms. Circulation 100:e20–e28.[Medline]
[Order article via Infotrieve]
- Epstein SE, Zhou YF, Zhu J (1999b). Potential role of cytomegalovirus in the pathogenesis of restenosis and atherosclerosis. Am Heart J 138:S476–S478.[CrossRef][Medline]
[Order article via Infotrieve]
- Epstein SE, Zhu J, Burnett MS, Zhou YF, Vercellotti G, Hajjar D (2000). Infection and atherosclerosis: potential roles of pathogen burden and molecular mimicry. Arterioscler Thromb Vasc Biol 20:1417–1420.[Abstract/Free Full Text]
- Espinola-Klein C, Rupprecht HJ, Blankenberg S, Bickel C, Kopp H, Victor A, et al. (2002). Impact of infectious burden on progression of carotid atherosclerosis. Stroke 33:2581–2586.[Abstract/Free Full Text]
- Fenton MJ, Golenbock DT (1998). LPS-binding proteins and receptors. J Leukoc Biol 64:25–32.[Abstract]
- Frantz S, Kobzik L, Kim YD, Fukazawa R, Medzhitov R, Lee RT, et al. (1999). Toll4 (TLR4) expression in cardiac myocytes in normal and failing myocardium. J Clin Invest 104:271–280.[Medline]
[Order article via Infotrieve]
- Gamonal J, Acevedo A, Bascones A, Jorge O, Silva A (2000). Levels of interleukin-1 beta, -8, and -10 and RANTES in gingival crevicular fluid and cell populations in adult periodontitis patients and the effect of periodontal treatment. J Periodontol 71:1535–1545.[CrossRef][Medline]
[Order article via Infotrieve]
- Geivelis M, Turner DW, Pederson ED, Lamberts BL (1993). Measurements of interleukin-6 in gingival crevicular fluid from adults with destructive periodontal disease. J Periodontol 64:980–983.[Medline]
[Order article via Infotrieve]
- Genco RJ (1996). Current view of risk factors for periodontal diseases. J Periodontol 67(10 Suppl):1041–1049.[Medline]
[Order article via Infotrieve]
- Georges JL, Rupprecht HJ, Blankenberg S, Poirier O, Bickel C, Hafner G, et al. (2003). Impact of pathogen burden in patients with coronary artery disease in relation to systemic inflammation and variation in genes encoding cytokines. Am J Cardiol 92:515–521.[CrossRef][Medline]
[Order article via Infotrieve]
- Giacona MB, Papapanou PN, Lamster IB, Rong LL, D’Agati VD, Schmidt AM, et al. (2004). Porphyromonas gingivalis induces its uptake by human macrophages and promotes foam cell formation in vitro. FEMS Microbiol Lett 241:95–101.[CrossRef][Medline]
[Order article via Infotrieve]
- Gibson FC 3rd, Hong C, Chou HH, Yumoto H, Chen J, Lien E, et al. (2004). Innate immune recognition of invasive bacteria accelerates atherosclerosis in apolipoprotein E-deficient mice. Circulation 109:2801–2806.[Abstract/Free Full Text]
- Gosling J, Slaymaker S, Gu L, Tseng S, Zlot CH, Young SG, et al. (1999). MCP-1 deficiency reduces susceptibility to atherosclerosis in mice that overexpress human apolipoprotein B. J Clin Invest 103:773–778.[Medline]
[Order article via Infotrieve]
- Grattan MT, Moreno-Cabral CE, Starnes VA, Oyer PE, Stinson EB, Shumway NE (1989). Cytomegalovirus infection is associated with cardiac allograft rejection and atherosclerosis. J Am Med Assoc 261:3561–3566.[Abstract/Free Full Text]
- Grau AJ, Buggle F, Lichy C, Brandt T, Becher H, Rudi J (2001). Helicobacter pylori infection as an independent risk factor for cerebral ischemia of atherothrombotic origin. J Neurol Sci 186:1–5.[CrossRef][Medline]
[Order article via Infotrieve]
- Greiffenberg L, Goebel W, Kim KS, Weiglein I, Bubert A, Engelbrecht F, et al. (1998). Interaction of Listeria monocytogenes with human brain microvascular endothelial cells: InlB-dependent invasion, long-term intracellular growth, and spread from macrophages to endothelial cells. Infect Immun 66:5260–5267.[Abstract/Free Full Text]
- Gupta S, Pablo AM, Jiang X, Wang N, Tall AR, Schindler C (1997). IFN-gamma potentiates atherosclerosis in ApoE knock-out mice. J Clin Invest 99:2752–2761.[Medline]
[Order article via Infotrieve]
- Hajishengallis G, Martin M, Sojar HT, Sharma A, Schifferle RE, DeNardin E, et al. (2002). Dependence of bacterial protein adhesins on toll-like receptors for proinflammatory cytokine induction. Clin Diagn Lab Immunol 9:403–411.[CrossRef][Medline]
[Order article via Infotrieve]
- Hanazawa S, Kawata Y, Takeshita A, Kumada H, Okithu M, Tanaka S, et al. (1993). Expression of monocyte chemoattractant protein 1 (MCP-1) in adult periodontal disease: increased monocyte chemotactic activity in crevicular fluids and induction of MCP-1 expression in gingival tissues. Infect Immun 61:5219–5224.[Abstract/Free Full Text]
- Haraszthy VI, Zambon JJ, Trevisan M, Zeid M, Genco RJ (2000). Identification of periodontal pathogens in atheromatous plaques. J Periodontol 71:1554–1560.[CrossRef][Medline]
[Order article via Infotrieve]
- Hektoen L (1896). The vascular changes of tuberculous meningitis. J Exp Med 1:112–163.[Abstract/Free Full Text]
- Henneke P, Takeuchi O, van Strijp JA, Guttormsen HK, Smith JA, Schromm AB, et al. (2001). Novel engagement of CD14 and multiple toll-like receptors by group B streptococci. J Immunol 167:7069–7076.[Abstract/Free Full Text]
- Herrera VL, Shen L, Lopez LV, Didishvili T, Zhang YX, Ruiz-Opazo N (2003). Chlamydia pneumoniae accelerates coronary artery disease progression in transgenic hyperlipidemia-genetic hypertension rat model. Mol Med 9:135–142.[CrossRef][Medline]
[Order article via Infotrieve]
- Hirschfeld M, Weis JJ, Toshchakov V, Salkowski CA, Cody MJ, Ward DC, et al. (2001). Signaling by toll-like receptor 2 and 4 agonists results in differential gene expression in murine macrophages. Infect Immun 69:1477–1482.[Abstract/Free Full Text]
- Holt SC, Ebersole J, Felton J, Brunsvold M, Kornman KS (1988). Implantation of Bacteroides gingivalis in nonhuman primates initiates progression of periodontitis. Science 239:55–57.[Abstract/Free Full Text]
- Holt SC, Kesavalu L, Walker S, Genco CA (1999). Virulence factors of Porphyromonas gingivalis. Periodontol 2000 20:168–238.[CrossRef]
- Howell TH, Ridker PM, Ajani UA, Hennekens CH, Christen WG (2001). Periodontal disease and risk of subsequent cardiovascular disease in U.S. male physicians. J Am Coll Cardiol 37:445–450.[Abstract/Free Full Text]
- Hu H, Pierce GN, Zhong G (1999). The atherogenic effects of chlamydia are dependent on serum cholesterol and specific to Chlamydia pneumoniae. J Clin Invest 103:747–753.[Medline]
[Order article via Infotrieve]
- Ikeda K, Utoguchi N, Makimoto H, Mizuguchi H, Nakagawa S, Mayumi T (1999). Different reactions of aortic and venular endothelial cell monolayers to histamine on macromolecular permeability: role of cAMP, cytosolic Ca2+ and F-actin. Inflammation 23:87–97.[CrossRef][Medline]
[Order article via Infotrieve]
- Imler JL, Hoffmann JA (2001). Toll receptors in innate immunity. Trends Cell Biol 11:304–311.[CrossRef][Medline]
[Order article via Infotrieve]
- Ishibashi S, Brown MS, Goldstein JL, Gerard RD, Hammer RE, Herz J (1993). Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery. J Clin Invest 92:883–893.[Medline]
[Order article via Infotrieve]
- Ishikawa I, Nakashima K, Koseki T, Nagasawa T, Watanabe H, Arakawa S, et al. (1997). Induction of the immune response to periodontopathic bacteria and its role in the pathogenesis of periodontitis. Periodontol 2000 14:79–111.[CrossRef]
- Ito T, Ikeda U (2003). Inflammatory cytokines and cardiovascular disease. Curr Drug Targets Inflamm Allergy 2:257–265.[CrossRef][Medline]
[Order article via Infotrieve]
- Jain A, Batista EL Jr, Serhan C, Stahl GL, Van Dyke TE (2003). Role for periodontitis in the progression of lipid deposition in an animal model. Infect Immun 71:6012–6018.[Abstract/Free Full Text]
- Janeway CA Jr, Medzhitov R (2002). Innate immune recognition. Annu Rev Immunol 20:197–216.[CrossRef][Medline]
[Order article via Infotrieve]
- Kahan T, Lundman P, Olsson G, Wendt M (2000). Greater than normal prevalence of seropositivity for Helicobacter pylori among patients who have suffered myocardial infarction. Coron Artery Dis 11:523–526.[CrossRef][Medline]
[Order article via Infotrieve]
- Kalayoglu MV, Byrne GI (1998). Induction of macrophage foam cell formation by Chlamydia pneumoniae. J Infect Dis 177:725–729.[Medline]
[Order article via Infotrieve]
- Kaukoranta-Tolvanen SS, Laitinen K, Saikku P, Leinonen M (1994). Chlamydia pneumoniae multiplies in human endothelial cells in vitro. Microb Pathog 16:313–319.[CrossRef][Medline]
[Order article via Infotrieve]
- Khlgatian M, Nassar H, Chou HH, Gibson FC 3rd, Genco CA (2002). Fimbria-dependent activation of cell adhesion molecule expression in Porphyromonas gingivalis-infected endothelial cells. Infect Immun 70:257–267.[Abstract/Free Full Text]
- Kiechl S, Lorenz E, Reindl M, Wiedermann CJ, Oberhollenzer F, Bonora E, et al. (2002). Toll-like receptor 4 polymorphisms and atherogenesis. N Engl J Med 347:185–192.[Abstract/Free Full Text]
- Kirii H, Niwa T, Yamada Y, Wada H, Saito K, Iwakura Y, et al. (2003). Lack of interleukin-1beta decreases the severity of atherosclerosis in ApoE-deficient mice. Arterioscler Thromb Vasc Biol 23:656–660.[Abstract/Free Full Text]
- Koch AE, Kunkel SL, Pearce WH, Shah MR, Parikh D, Evanoff HL, et al. (1993). Enhanced production of the chemotactic cytokines interleukin-8 and monocyte chemoattractant protein-1 in human abdominal aortic aneurysms. Am J Pathol 142:1423–1431.[Abstract]
- Kuramitsu HK, Qi M, Kang IC, Chen W (2001). Role for periodontal bacteria in cardiovascular diseases. Ann Periodontol 6:41–47.[CrossRef][Medline]
[Order article via Infotrieve]
- Kusumoto Y, Hirano H, Saitoh K, Yamada S, Takedachi M, Nozaki T, et al. (2004). Human gingival epithelial cells produce chemotactic factors interleukin-8 and monocyte chemoattractant protein-1 after stimulation with Porphyromonas gingivalis via toll-like receptor 2. J Periodontol 75:370–379.[CrossRef][Medline]
[Order article via Infotrieve]
- Lalla E, Lamster IB, Hofmann MA, Bucciarelli L, Jerud AP, Tucker S, et al. (2003). Oral infection with a periodontal pathogen accelerates early atherosclerosis in apolipoprotein e-null mice. Arterioscler Thromb Vasc Biol 23:1405–1411.[Abstract/Free Full Text]
- Laman JD, Schoneveld AH, Moll FL, van Meurs M, Pasterkamp G (2002). Significance of peptidoglycan, a proinflammatory bacterial antigen in atherosclerotic arteries and its association with vulnerable plaques. Am J Cardiol 90:119–123.[CrossRef][Medline]
[Order article via Infotrieve]
- Lamb DJ, El-Sankary W, Ferns GA (2003). Molecular mimicry in atherosclerosis: a role for heat shock proteins in immunisation. Atherosclerosis 167:177–185.
- Landi L, Amar S, Polins AS, Van Dyke TE (1997). Host mechanisms in the pathogenesis of periodontal disease. Curr Opin Periodontol 4:3–10.[Medline]
[Order article via Infotrieve]
- Li L, Messas E, Batista EL Jr, Levine RA, Amar S (2002). Porphyromonas gingivalis infection accelerates the progression of atherosclerosis in a heterozygous apolipoprotein E-deficient murine model. Circulation 105:861–867.[Abstract/Free Full Text]
- Libby P (2002). Inflammation in atherosclerosis. Nature 420:868–874.[CrossRef][Medline]
[Order article via Infotrieve]
- Libby P, Ridker PM, Maseri A (2002). Inflammation and atherosclerosis. Circulation 105:1135–1143.[Abstract/Free Full Text]
- Liu L, Hu H, Ji H, Murdin AD, Pierce GN, Zhong G (2000). Chlamydia pneumoniae infection significantly exacerbates aortic atherosclerosis in an LDLR–/– mouse model within six months. Mol Cell Biochem 215:123–128.[CrossRef][Medline]
[Order article via Infotrieve]
- Liuba P, Pesonen E, Paakkari I, Batra S, Andersen L, Forslid A, et al. (2003). Co-infection with Chlamydia pneumoniae and Helicobacter pylori results in vascular endothelial dysfunction and enhanced VCAM-1 expression in apoE-knockout mice. J Vasc Res 40:115–122.[CrossRef][Medline]
[Order article via Infotrieve]
- Lunardi C, Bason C, Navone R, Millo E, Damonte G, Corrocher R, et al. (2000). Systemic sclerosis immunoglobulin G autoantibodies bind the human cytomegalovirus late protein UL94 and induce apoptosis in human endothelial cells. Nat Med 6:1183–1186.[CrossRef][Medline]
[Order article via Infotrieve]
- Lutgens E, Daemen M, Kockx M, Doevendans P, Hofker M, Havekes L, et al. (1999). Atherosclerosis in APOE*3-Leiden transgenic mice: from proliferative to atheromatous stage. Circulation 99:276–283.[Abstract/Free Full Text]
- MacIntyre A, Abramov R, Hammond CJ, Hudson AP, Arking EJ, Little CS, et al. (2003). Chlamydia pneumoniae infection promotes the transmigration of monocytes through human brain endothelial cells. J Neurosci Res 71:740–750.[CrossRef][Medline]
[Order article via Infotrieve]
- Madianos PN, Papapanou PN, Sandros J (1997). Porphyromonas gingivalis infection of oral epithelium inhibits neutrophil transepithelial migration. Infect Immun 65:3983–3990.[Abstract/Free Full Text]
- Massari P, Henneke P, Ho Y, Latz E, Golenbock DT, Wetzler LM (2002). Cutting edge: immune stimulation by Neisserial porins is toll-like receptor 2 and MyD88 dependent. J Immunol 168:1533–1537.[Abstract/Free Full Text]
- Melnick JL, Petrie BL, Dreesman GR, Burek J, McCollum CH, DeBakey ME (1983). Cytomegalovirus antigen within human arterial smooth muscle cells. Lancet 2:644–647.[Medline]
[Order article via Infotrieve]
- Messini M, Skourti I, Markopulos E, Koutsia-Carouzou C, Kyriakopoulou E, Kostaki S, et al. (1999). Bacteremia after dental treatment in mentally handicapped people. J Clin Periodontol 26:469–473.[CrossRef][Medline]
[Order article via Infotrieve]
- Michelsen KS, Wong MH, Shah PK, Zhang W, Yano J, Doherty TM, et al. (2004). Lack of Toll-like receptor 4 or myeloid differentiation factor 88 reduces atherosclerosis and alters plaque phenotype in mice deficient in apolipoprotein E. Proc Natl Acad Sci USA 101:10679–10684.[Abstract/Free Full Text]
- Miyakawa H, Honma K, Qi M, Kuramitsu HK (2004). Interaction of Porphyromonas gingivalis with low-density lipoproteins: implications for a role for periodontitis in atherosclerosis. J Periodontal Res 39:1–9.[CrossRef][Medline]
[Order article via Infotrieve]
- Moazed TC, Campbell LA, Rosenfeld ME, Grayston JT, Kuo CC (1999). Chlamydia pneumoniae infection accelerates the progression of atherosclerosis in apolipoprotein E-deficient mice. J Infect Dis 180:238–241.[CrossRef][Medline]
[Order article via Infotrieve]
- Morris TE, Mattox PA, Shipley GD, Wagner CR, Hosenpud JD (1993). The pattern of cytokine messenger RNA expression in human aortic endothelial cells is different from that of human umbilical vein endothelial cells. Transpl Immunol 1:137–142.[CrossRef][Medline]
[Order article via Infotrieve]
- Morrison HI, Ellison LF, Taylor GW (1999). Periodontal disease and risk of fatal coronary heart and cerebrovascular diseases. J Cardiovasc Risk 6:7–11.[Medline]
[Order article via Infotrieve]
- Muzio M, Bosisio D, Polentarutti N, D’Amico G, Stoppacciaro A, Mancinelli R, et al. (2000a). Differential expression and regulation of toll-like receptors (TLR) in human leukocytes: selective expression of TLR3 in dendritic cells. J Immunol 164:5998–6004.[Abstract/Free Full Text]
- Muzio M, Polentarutti N, Bosisio D, Prahladan MK, Mantovani A (2000b). Toll-like receptors: a growing family of immune receptors that are differentially expressed and regulated by different leukocytes. J Leukoc Biol 67:450–456.[Abstract]
- Nassar H, Chou HH, Khlgatian M, Gibson FC 3rd, Van Dyke TE, Genco CA (2002). Role for fimbriae and lysine-specific cysteine proteinase gingipain K in expression of interleukin-8 and monocyte chemoattractant protein in Porphyromonas gingivalis-infected endothelial cells. Infect Immun 70:268–276.[Abstract/Free Full Text]
- Noack B, Genco RJ, Trevisan M, Grossi S, Zambon JJ, De Nardin E (2001). Periodontal infections contribute to elevated systemic C-reactive protein level. J Periodontol 72:1221–1227.[CrossRef][Medline]
[Order article via Infotrieve]
- Nottet HS, Persidsky Y, Sasseville VG, Nukuna AN, Bock P, Zhai QH, et al. (1996). Mechanisms for the transendothelial migration of HIV-1-infected monocytes into brain. J Immunol 156:1284–1295.[Abstract]
- Paigen B, Holmes PA, Mitchell D, Albee D (1987). Comparison of atherosclerotic lesions and HDL-lipid levels in male, female, and testosterone-treated female mice from strains C57BL/6, BALB/c, and C3H. Atherosclerosis 64:215–221.[CrossRef][Medline]
[Order article via Infotrieve]
- Pietroiusti A, Diomedi M, Silvestrini M, Cupini LM, Luzzi I, Gomez-Miguel MJ, et al. (2002). Cytotoxin-associated gene-A-positive Helicobacter pylori strains are associated with atherosclerotic stroke. Circulation 106:580–584.[Abstract/Free Full Text]
- Plump AS, Smith JD, Hayek T, Aalto-Setala K, Walsh A, Verstuyft JG, et al. (1992). Severe hypercholesterolemia and atherosclerosis in apolipoprotein E-deficient mice created by homologous recombination in ES cells. Cell 71:343–353.[CrossRef][Medline]
[Order article via Infotrieve]
- Progulske-Fox A, Kozarov E, Dorn B, Dunn W Jr, Burks J, Wu Y (1999). Porphyromonas gingivalis virulence factors and invasion of cells of the cardiovascular system. J Periodontal Res 34:393–399.[CrossRef][Medline]
[Order article via Infotrieve]
- Pulendran B, Kumar P, Cutler CW, Mohamadzadeh M, Van Dyke T, Banchereau J (2001). Lipopolysaccharides from distinct pathogens induce different classes of immune responses in vivo. J Immunol 167:5067–5076.[Abstract/Free Full Text]
- Pussinen PJ, Jousilahti P, Alfthan G, Palosuo T, Asikainen S, Salomaa V (2003). Antibodies to periodontal pathogens are associated with coronary heart disease. Arterioscler Thromb Vasc Biol 23:1250–1254.[Abstract/Free Full Text]
- Qi M, Miyakawa H, Kuramitsu HK (2003). Porphyromonas gingivalis induces murine macrophage foam cell formation. Microb Pathog 35:259–267.[CrossRef][Medline]
[Order article via Infotrieve]
- Reape TJ, Groot PH (1999). Chemokines and atherosclerosis. Atherosclerosis 147:213–225.[CrossRef][Medline]
[Order article via Infotrieve]
- Roberts FA, McCaffery KA, Michalek SM (1997). Profile of cytokine mRNA expression in chronic adult periodontitis. J Dent Res 76:1833–1839.
- Ross R (1999). Atherosclerosis is an inflammatory disease. Am Heart J 138:S419–S420.[CrossRef][Medline]
[Order article via Infotrieve]
- Rothstein NM, Quinn TC, Madico G, Gaydos CA, Lowenstein CJ (2001). Effect of azithromycin on murine arteriosclerosis exacerbated by Chlamydia pneumoniae. J Infect Dis 183:232–238.[CrossRef][Medline]
[Order article via Infotrieve]
- Salvi GE, Brown CE, Fujihashi K, Kiyono H, Smith FW, Beck JD, et al. (1998). Inflammatory mediators of the terminal dentition in adult and early onset periodontitis. J Periodontal Res 33:212–225.[CrossRef][Medline]
[Order article via Infotrieve]
- Scannapieco FA, Genco RJ (1999). Association of periodontal infections with atherosclerotic and pulmonary diseases. J Periodontal Res 34:340–345.[CrossRef][Medline]
[Order article via Infotrieve]
- Slade GD, Beck JD (1999). Plausibility of periodontal disease estimates from NHANES III. J Public Health Dent 59:67–72.[Medline]
[Order article via Infotrieve]
- Slade GD, Ghezzi EM, Heiss G, Beck JD, Riche E, Offenbacher S (2003). Relationship between periodontal disease and C-reactive protein among adults in the Atherosclerosis Risk in Communities study. Arch Intern Med 163:1172–1179.[Abstract/Free Full Text]
- Span AH, Van Boven CP, Bruggeman CA (1989). The effect of cytomegalovirus infection on the adherence of polymorphonuclear leucocytes to endothelial cells. Eur J Clin Invest 19:542–548.[Medline]
[Order article via Infotrieve]
- Spence JD, Norris J (2003). Infection, inflammation, and atherosclerosis. Stroke 34:333–334.[Free Full Text]
- Spriggs MK (1996). One step ahead of the game: viral immunomodulatory molecules. Annu Rev Immunol 14:101–130.[CrossRef][Medline]
[Order article via Infotrieve]
- Springer TA (1990). Adhesion receptors of the immune system. Nature 346:425–434.[CrossRef][Medline]
[Order article via Infotrieve]
- Srisatjaluk R, Doyle RJ, Justus DE (1999). Outer membrane vesicles of Porphyromonas gingivalis inhibit IFN-gamma-mediated MHC class II expression by human vascular endothelial cells. Microb Pathog 27:81–91.[CrossRef][Medline]
[Order article via Infotrieve]
- Stary HC, Chandler AB, Glagov S, Guyton JR, Insull W Jr, Rosenfeld ME, et al. (1994). A definition of initial, fatty streak, and intermediate lesions of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association. Circulation 89:2462–2478.[Abstract/Free Full Text]
- Stary HC, Chandler AB, Dinsmore RE, Fuster V, Glagov S, Insull W Jr, et al. (1995). A definition of advanced types of atherosclerotic lesions and a histological classification of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association. Circulation 92:1355–1374.[Abstract/Free Full Text]
- Takeda K, Akira S (2005). Toll-like receptors in innate immunity. Int Immunol 17:1–14.[Abstract/Free Full Text]
- Tasaki N, Nakajima M, Yamamoto H, Imazu M, Okimoto T, Otsuka M, et al. (2003). Influence of Chlamydia pneumoniae infection on aortic stiffness in healthy young men. Atherosclerosis 171:117–122.
- Teragawa H, Fukuda Y, Matsuda K, Ueda K, Higashi Y, Oshima T, et al. (2004). Relation between C reactive protein concentrations and coronary microvascular endothelial function. Heart 90:750–754.[Abstract/Free Full Text]
- Thoma-Uszynski S, Stenger S, Takeuchi O, Ochoa MT, Engele M, Sieling PA, et al. (2001). Induction of direct antimicrobial activity through mammalian toll-like receptors. Science 291:1544–1547.[Abstract/Free Full Text]
- Tsai CC, Ho YP, Chen CC (1995). Levels of interleukin-1 beta and interleukin-8 in gingival crevicular fluids in adult periodontitis. J Periodontol 66:852–859.[Medline]
[Order article via Infotrieve]
- Underhill DM, Ozinsky A (2002). Toll-like receptors: key mediators of microbe detection. Curr Opin Immunol 14:103–110.[CrossRef][Medline]
[Order article via Infotrieve]
- Vasselon T, Detmers PA (2002). Toll receptors: a central element in innate immune responses. Infect Immun 70:1033–1041.[Free Full Text]
- Visintin A, Mazzoni A, Spitzer JH, Wyllie DH, Dower SK, Segal DM (2001). Regulation of Toll-like receptors in human monocytes and dendritic cells. J Immunol 166:249–255.[Abstract/Free Full Text]
- Vita JA, Loscalzo J (2002). Shouldering the risk factor burden: infection, atherosclerosis, and the vascular endothelium. Circulation 106:164–166.[Free Full Text]
- Wang PL, Shinohara M, Murakawa N, Endo M, Sakata S, Okamura M, et al. (1999). Effect of cysteine protease of Porphyromonas gingivalis on adhesion molecules in gingival epithelial cells. Jpn J Pharmacol 80:75–79.[CrossRef][Medline]
[Order article via Infotrieve]
- Wick G, Schett G, Amberger A, Kleindienst R, Xu Q (1995). Is atherosclerosis an immunologically mediated disease? Immunol Today 16:27–33.[CrossRef][Medline]
[Order article via Infotrieve]
- Wu T, Trevisan M, Genco RJ, Dorn JP, Falkner KL, Sempos CT (2000). Periodontal disease and risk of cerebrovascular disease: the first National Health and Nutrition Examination Survey and its follow-up study. Arch Intern Med 160:2749–2755.[Abstract/Free Full Text]
- Xu Q (2003). Infections, heat shock proteins, and atherosclerosis. Curr Opin Cardiol 18:245–252.[CrossRef][Medline]
[Order article via Infotrieve]
- Xu XH, Shah PK, Faure E, Equils O, Thomas L, Fishbein MC, et al. (2001). Toll-like receptor-4 is expressed by macrophages in murine and human lipid-rich atherosclerotic plaques and upregulated by oxidized LDL. Circulation 104:3103–3108.[Abstract/Free Full Text]
- Yamazaki K, Ohsawa Y, Itoh H, Ueki K, Tabeta K, Oda T, et al. (2004). T-cell clonality to Porphyromonas gingivalis and human heat shock protein 60s in patients with atherosclerosis and periodontitis. Oral Microbiol Immunol 19:160–167.[Medline]
[Order article via Infotrieve]
- Yang IA, Holloway JW, Ye S (2003). TLR4 Asp299Gly polymorphism is not associated with coronary artery stenosis. Atherosclerosis 170:187–190.
- Zhou Q, Desta T, Fenton M, Graves DT, Amar S (2005). Cytokine profiling of macrophages exposed to Porphyromonas gingivalis, its lipopolysaccharide, or its FimA protein. Infect Immun 73:935–943.[Abstract/Free Full Text]
- Zhou YF, Shou M, Guetta E, Guzman R, Unger EF, Yu ZX, et al. (1999). Cytomegalovirus infection of rats increases the neointimal response to vascular injury without consistent evidence of direct infection of the vascular wall. Circulation 100:1569–1575.[Abstract/Free Full Text]
Journal of Dental Research, Vol. 85, No. 2,
106-121 (2006)
DOI: 10.1177/154405910608500202
 CiteULike  Complore  Connotea  Del.icio.us  Digg  Reddit  Technorati  Twitter What's this?
This article has been cited by other articles:
|
|
|
|
 
Y. Hasegawa, J. Iwami, K. Sato, Y. Park, K. Nishikawa, T. Atsumi, K. Moriguchi, Y. Murakami, R. J. Lamont, H. Nakamura, et al.
Anchoring and length regulation of Porphyromonas gingivalis Mfa1 fimbriae by the downstream gene product Mfa2
Microbiology,
October 1, 2009;
155(10):
3333 - 3347.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Hajishengallis, M. Wang, and S. Liang
Induction of Distinct TLR2-Mediated Proinflammatory and Proadhesive Signaling Pathways in Response to Porphyromonas gingivalis Fimbriae
J. Immunol.,
June 1, 2009;
182(11):
6690 - 6696.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Imai, K. Ochiai, and T. Okamoto
Reactivation of Latent HIV-1 Infection by the Periodontopathic Bacterium Porphyromonas gingivalis Involves Histone Modification
J. Immunol.,
March 15, 2009;
182(6):
3688 - 3695.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Walters, P. Rodrigues, M. Belanger, J. Whitlock, and A. Progulske-Fox
Analysis of a Band 7/MEC-2 Family Gene of Porphyromonas gingivalis
Journal of Dental Research,
January 1, 2009;
88(1):
34 - 38.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
I. N. Baranova, R. Kurlander, A. V. Bocharov, T. G. Vishnyakova, Z. Chen, A. T. Remaley, G. Csako, A. P. Patterson, and T. L. Eggerman
Role of Human CD36 in Bacterial Recognition, Phagocytosis, and Pathogen-Induced JNK-Mediated Signaling
J. Immunol.,
November 15, 2008;
181(10):
7147 - 7156.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Koizumi, T. Kurita-Ochiai, S. Oguchi, and M. Yamamoto
Nasal Immunization with Porphyromonas gingivalis Outer Membrane Protein Decreases P. gingivalis-Induced Atherosclerosis and Inflammation in Spontaneously Hyperlipidemic Mice
Infect. Immun.,
July 1, 2008;
76(7):
2958 - 2965.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Q. Zhou and S. Amar
Identification of Signaling Pathways in Macrophage Exposed to Porphyromonas gingivalis or to Its Purified Cell Wall Components
J. Immunol.,
December 1, 2007;
179(11):
7777 - 7790.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Hajishengallis, M.-A. K. Shakhatreh, M. Wang, and S. Liang
Complement Receptor 3 Blockade Promotes IL-12-Mediated Clearance of Porphyromonas gingivalis and Negates Its Virulence In Vivo
J. Immunol.,
August 15, 2007;
179(4):
2359 - 2367.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. M. Lepper, C. Schumann, K. Triantafilou, F. M. Rasche, T. Schuster, H. Frank, E. M. Schneider, M. Triantafilou, and M. von Eynatten
Association of Lipopolysaccharide-Binding Protein and Coronary Artery Disease in Men
J. Am. Coll. Cardiol.,
July 3, 2007;
50(1):
25 - 31.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. Carayol, J. Chen, F. Yang, T. Jin, L. Jin, D. States, and C.-Y. Wang
A Dominant Function of IKK/NF-{kappa}B Signaling in Global Lipopolysaccharide-induced Gene Expression
J. Biol. Chem.,
October 13, 2006;
281(41):
31142 - 31151.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Hasebe, N. D. Pennock, H.-H. Mu, F. V. Chan, M. L. Taylor, and B. C. Cole
A Microbial TLR2 Agonist Imparts Macrophage-Activating Ability to Apolipoprotein A-1
J. Immunol.,
October 1, 2006;
177(7):
4826 - 4832.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. Harokopakis, M. H. Albzreh, M. H. Martin, and G. Hajishengallis
TLR2 Transmodulates Monocyte Adhesion and Transmigration via Rac1- and PI3K-Mediated Inside-Out Signaling in Response to Porphyromonas gingivalis Fimbriae.
J. Immunol.,
June 15, 2006;
176(12):
7645 - 7656.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
TOP
ABSTRACT
INTRODUCTION