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Osteopontin and Mucosal Protection

CIHR Group in Matrix Dynamics, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, ON M5G 1G6, Canada

Correspondence: ^* corresponding author, ron.zohar{at}utoronto.ca

	ABSTRACT

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
Protection of mucosal tissues of the oral cavity, intestines, respiratory tract, and urogenital tract from the constant challenge of pathogens is achieved by the combined barrier function of the lining epithelia and specialized immune cells. Recent studies have indicated that osteopontin (OPN) has a pivotal role in the development of immune responses and in the tissue destruction and the subsequent repair processes associated with inflammatory diseases. While expression of OPN is increased in immune cells—including neutrophils, macrophages, T- and B-lymphocytes—and in epithelial, endothelial, and fibroblastic cells of inflamed tissues, deciphering the specific functions of OPN has been difficult. In part, this is due to the broad range of biological activities of OPN that are mediated by multiple receptors which recognize several signaling motifs whose activities are influenced by post-translational modifications and proteolytic processing of OPN. Understanding the role of OPN in mucosal inflammation is further complicated by its contributions to the barrier function of the lining epithelia and the complexity of the specialized mucosal immune system. In an attempt to provide some insights into the involvement of OPN in mucosal diseases, this review summarizes current knowledge of the biological activities of OPN involved in the development of inflammatory responses and in wound healing, and indicates how these activities may affect the protection of mucosal tissues.

Key Words: osteopontin • mucosa • immunity

	INTRODUCTION

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
Osteopontin (OPN) is a phosphorylated glycoprotein that is expressed by a broad range of tissues and cells (Sodek et al., 2000). Although originally characterized as a bone matrix protein (Prince and Butler, 1987), T-lymphocyte activation protein (Eta-1) (Patarca et al., 1993), and cell transformation-associated protein (Craig et al., 1988), OPN functions as a matricellular protein with diverse biological activities mediated by multiple cell-surface receptors (Giachelli and Steitz, 2000). Interest in OPN has focused on its role as an inflammatory cytokine in response to recent studies showing that OPN is up-regulated in inflammatory diseases and is required for the development of cellular immunity (Ashkar et al., 2000; O’Regan, 2003) and wound healing (Liaw et al., 1998; Rittling et al., 1998). In the absence of OPN, the development of many inflammatory diseases is attenuated (Miyazaki et al., 1995; Noiri et al., 1999; Chabas et al., 2001; O’Regan et al., 2001; Jansson et al., 2002; Yumoto et al., 2002). Indeed, OPN expression seems to be up-regulated in almost every wounded organ, including: brain, liver, gastrointestinal tract, lung, bone, cardiac tissue, joints, and kidney and various tumors. Moreover, OPN expression during inflammation is not limited to specific cell lineages but involves many different cells, including epithelial, mesenchymal, as well as immune cells, in the inflamed tissues (Fig. 1). The increased expression of OPN is associated with increased cell mobilization, survival, and activity and is reflected in elevated concentrations of OPN in tissue fluids and plasma, which has potential diagnostic and prognostic value for cancer progression and tumor burden (Tuck et al., 2003), as well as for inflammatory disease progression in the joints, cardiac and nervous systems, and in the intestines (Reinholt et al., 1990; Gassler et al., 2002; Ohshima et al., 2002a.b; Koguchi et al., 2003; Tamura et al., 2003; Vogt et al., 2003).

View larger version (52K): [in this window] [in a new window]   Figure 1. Expression of OPN in inflamed tissues and by inflammatory cells. (A) Immunohistochemical staining for OPN in the normal and inflamed colon. Photomicrographs of sections of the distal colon of 8-week-old mice subjected to experimental colitis were immunostained for OPN and compared with control tissues. Increased staining intensity for OPN is evident in the epithelium and submucosal tissues of the diseased colon (mag. X200). (B) Immunofluorescent staining for OPN (red) and CD44 (green) in isolated neutrophils and macrophages. OPN in neutrophils is present throughout the cells, while CD44 is localized to the periphery of non-polarized neutrophils and in the trailing uropod (green arrowheads) in polarized cells. The distribution of OPN and CD44 is unchanged in CD44–/– and OPN–/– cells. In macrophages, the OPN is seen to co-localize (yellow arrowheads) with CD44 (green arrowheads) in the cell periphery of migrating cells. OPN–/– and particularly CD44–/– macrophages have reduced cell processes and appear more rounded, the OPN in CD44–/– cells being more centrally distributed.

	OPN STRUCTURE AND RELATED FUNCTIONS

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
To understand how OPN has the ability to influence a broad range of biological activities requires an appreciation of its structure and functional motifs (Fig. 2). Since several detailed reviews on OPN have been published recently (Giachelli and Steitz, 2000; Sodek et al., 2000; Denhardt et al., 2001a,b; O’Regan, 2003), we include only a brief description of the salient features of OPN and focus on those properties of OPN that are particularly pertinent to mucosal defense. OPN is expressed by a single gene in a cluster of SIBLING family proteins that share structural and functional properties (Fisher and Fedarko, 2003) on the long arm of chromosome 4 in humans and chromosome 5 in mice. OPN is synthesized as a ~ 34-kDa nascent protein that is extensively modified by phosphorylation and glyco-sylation and sulphation prior to its secretion as a largely unstructured 44- to 75-kDa protein (Sodek et al., 2000). The heterogeneity of the secreted protein reflects differences in these post-translational modifications, which have been related to different functional activities associated with mineralization (Nagata et al., 1989; Sodek et al., 2000) and cell attachment and signaling (Ashkar et al., 2000; Zhu et al., 2001; Suzuki et al., 2002; Weber et al., 2002; Chellaiah et al., 2003). However, most of the known functional activities of OPN can be attributed primarily to highly conserved structural motifs involved in binding mineral and cell-surface CD44 and integrin receptors (Fig. 2).

View larger version (25K): [in this window] [in a new window]   Figure 2. The locations of 2 integrin-binding sites and 3 CD44 signaling sites are shown (the precise location of the third CD44 signaling motif in the carboxy-terminal thrombin fragment has not been identified). The cryptic SLAYGLR (SLVVGLR in human OPN) integrin-binding site, which is contiguous with the RGD domain, is exposed by thrombin digestion of the adjacent arginine. Thrombin digestion also increases the activity of the RGD. The sites of post-translational modifications are adapted from rat OPN, in which 10–11 phosphorylation sites are modified per molecule. M, methionine; S, serine; L, leucine; D, aspartate; R, arginine; G, glycine; N, asparagine; T, threonine.

CD44 has been identified as a receptor for OPN through which chemotactic (Weber et al., 1996) and cytokine responses of macrophages (Ashkar et al., 2000) have been demonstrated. Activities mediated by the CD44 receptor have implicated the amino-terminal peptide sequence (Fisher and Fedarko, 2003), a cryptic site near a central thrombin cleavage site (Lin and Yang-Yen, 2001), and an unidentified region in the C-terminal half of the molecule (Weber et al., 2002). The amino-terminal peptide has strong chemotactic activity for macrophages that can be blocked by CD44 antibodies and antibodies to the amino-terminus of OPN (Batista-da-Silva et al., unpublished observations), while Thr 147 in the murine OPN cryptic motif may be important for OPN signaling through the CD44 receptor in B-cells (Lin and Yang-Yen, 2001) (Fig. 2). Notably, chemotaxis of macrophages toward formyl-met-leu-phe (fMLP) in vivo is inhibited by antibodies to OPN (Giachelli et al., 1998). However, the interaction between OPN and CD44 may not be direct (Smith and Giachelli, 1998), and, for CD44, variant forms may require non-RGD-dependent mediation by the β1 integrin (Katagiri et al., 1999).

The pleiotropic effects of OPN mediated by the different receptors provide the basis for its emergence as a cytokine that is highly expressed in various pathologies involving inflammation and cancer progression and metastasis, as well as in the pathophysiological processes of wound healing (Giachelli et al., 1998; Liaw et al., 1998; Giachelli and Steitz, 2000; O’Regan and Berman, 2000; Sodek et al., 2000; Lekic et al., 2001; Leali et al., 2003). Moreover, the frequent up-regulation of OPN in a variety of cells in response to a broad range of adverse conditions suggests that it functions as a stress-related glycoprotein. In the immune system, an increased transcription of OPN (identified as early T-lymphocyte activation 1; eta-1) in T-cells (Patarca et al., 1989) was subsequently linked to its suppression of T-lymphocyte function and enhancement of B-lymphocyte proliferation and antibody production (Lampe et al., 1991; Weber et al., 1996). OPN is now recognized as a key cytokine involved in immune cell recruitment and type-1 (Th1) cytokine expression at sites of inflammation (Ashkar et al., 2000; Chabas et al., 2001; Jansson et al., 2002), and it has been proposed that it be considered a new interleukin family member (IL-28; G Weber, International Conference on Osteopontin and Related Proteins, 3rd ICORP Meeting, San Antonio, May, 2002; Weber, 2002). Macrophages are central to the innate immune response (Fig. 3) and are a primary target of OPN. Ligation of CD44 receptors and the β₃-integrin by separate domains of OPN attract macrophages and stimulate cytokine and metalloproteinase production, respectively (Weber, 2002). OPN has also been reported to bind and activate pro-stromelysin (pro-MMP3) (Fedarko et al., 2000). Since the expression of this metalloproteinase is increased in wound healing, this surprising activity of OPN may be significant for the resolution of inflammatory diseases.

View larger version (28K): [in this window] [in a new window]   Figure 3. Diagram showing possible protective functions of OPN that affect the patency of the epithelium, both directly and indirectly, through the innate immune response to mucosal disease. Noxious agents (bacteria, bacterial products, and antigens) cause epithelial damage, resulting in IL-1 and IL-8 release, which attracts neutrophils and macrophages. This immediate response is controlled by secretion of pro-inflammatory cytokines and the expression of Toll-like receptors (TLRs) and chemokine receptors. OPN expressed by epithelial and immune cells acts as a chemoattractant to macrophages and neutrophils and regulates their phagocytic activity, reactive oxidative burst (ROS) and release of cytokines, and proteolytic enzymes. A protracted innate response will cause further destruction of the epithelial barrier.

In addition to the various secreted forms of OPN, the existence of an intracellular form of OPN (iOPN) that co-localizes with CD44 in migrating fibroblasts, macrophages, and osteoclasts has been reported (Zohar et al., 2000; Suzuki et al., 2002; Zhu et al., 2004). This novel form of OPN—which appears to modulate cytoskeleton-related functions, including cell motility and survival (Zohar et al., 2004), and mediates IFN expression in plasmacytoid dendritic cells (Shinohara et al., 2006)— introduces a further layer of complexity in deciphering the roles of different forms of OPN.

	OPN AND INFLAMMATORY DISEASES

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
During inflammation, OPN is secreted by T-lymphocytes and activated macrophages and, subsequently, by proliferating fibroblasts and myofibroblasts during granulation tissue formation (Ashkar et al., 2000; O’Regan and Berman, 2000). In the absence of OPN expression, macrophage migration and adhesion are impaired (Giachelli et al., 1998; Zhu et al., 2004), while the ability of OPN to promote fibrosis is consistent with the impaired wound healing in OPN-null mice (Liaw et al., 1998; Jander et al., 2002; Yumoto et al., 2002) and with studies demonstrating that OPN promotes survival of fibroblasts, as well as endothelial cells involved in neovascularization (Denhardt et al., 2001a). The survival-promoting effects of OPN in endothelial cells are mediated by vβ3 activation and signaling through Ras and src tyrosine kinase, followed by activation of NF-B (Scatena et al., 1998). In fibroblastic cells, the lack of OPN expression leads to caspase-independent necrosis, promoted by oxidants (Zohar et al., 2004). In contrast to programmed cell death, where dying cells undergo phagocytosis and clear the way for new tissues and cells, necrotic cell death is strongly associated with an exacerbation of inflammation and an increase of tissue destruction. Cell necrosis is a rapid form of cell death, in which damage and rapid permeabilization of cell membranes lead to the release of intracellular contents. The released cellular components act as irritants, recruiting more phagocytes (PMN, macrophages) and aggravating inflammation, and resulting in tissue destruction (Ina et al., 1999; Paleolog, 2003; Kurtovic and Segal, 2004).

In many inflammatory models, the formation of granulation tissue and the intensity of inflammatory reactions are dramatically reduced in the absence of OPN expression (O’Regan et al., 2001). Thus, the development of inflammatory diseases—such as lung (Miyazaki et al., 1995; O’Regan et al., 2001) and kidney (Noiri et al., 1999) fibrosis, arthritis (Yumoto et al., 2002) and multiple sclerosis (Chabas et al., 2001; Jansson et al., 2002)—is markedly suppressed in OPN-null mice. However, the critical role of OPN has been questioned in arthritis and experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, because the development of inflammation and its attenuation in the absence of OPN expression appear to be mouse-strain-specific, and, in some studies, concerns over the removal of flanking genes in back-crossed OPN-null mice have been raised (Blom et al., 2003; Jacobs et al., 2004). Consequently, the demonstration that arthritis-associated inflammation (Yamamoto et al., 2003) and concanavalin A-induced hepatitis (Diao et al., 2004) can be suppressed by antibodies directed at the cryptic "SLAYGLR" sequence in mice provides important alternative evidence of the pivotal role of OPN in the inflammatory response, by an approach that is not subject to compensatory mechanisms that can arise in knock-out mice. Importantly, in all of these pathologies, OPN expression by activated macrophages, T-cells, and fibroblastic cells is increased as part of the inflammatory response and in the subsequent repair process (Fig. 1), which also supports the significant contribution OPN makes in the progression and sequelae of inflammatory diseases. High levels of OPN expression are also a hallmark of monocytic granulomatous reactions in the context of tuberculosis and silicosis (Nau et al., 1999; O’Regan et al., 1999).

While most studies have generally concluded that OPN is a key regulator of cell-mediated inflammation, the potential role of OPN in protecting tissues from disease and/or excessive inflammatory destruction has largely been ignored. The apparent detrimental effects of OPN relate to its pro-inflammatory effects on macrophages, which respond by increased production of the Th1 cytokines IL-12 and IFN- and decreased production of the Th2 cytokine IL-10, thereby polarizing the immune response to the Th1 pathway (Ashkar et al., 2000). These combined effects promote a protracted inflammation that is characteristic of autoimmune diseases, in which OPN may also contribute prominently (Lampe et al., 1991; Ashkar et al., 2000; Chabas et al., 2001). Notably, in OPN-null mice, the Th1 cytokines are reduced, while the Th2 cytokines are elevated. The protective effects of OPN may be more evident in mucosal inflammation, in which the patency of an epithelial lining is important for mediating injury and antigen presentation. However, while skin wound repair has been analyzed in OPN-null mice (Liaw et al., 1998), few studies have examined the role of OPN in mucosal disease. Following the creation of incision wounds in skin, the expression of OPN is increased within 6 hrs. However, in the absence of OPN expression, matrix production is impaired, and cell debris accumulates at the wound site (Liaw et al., 1998). Since neutrophil infiltration is an immediate response to mucosal injury that leads to the development of an acute inflammation, these observations suggest that, in OPN-null mice, there is an increased destructive activity of neutrophils due to slow clearance by macrophages, which may also have reduced phagocytic activity. In addition to the delayed resolution of the innate immune response, fibroblast function also appears to be compromised. This interpretation is consistent with the increased tissue destruction and markedly elevated (Fig. 1) PMN activity that we have observed in an acute colitis model in OPN-null mice, in which little epithelial regeneration is observed during remission in the absence of OPN expression (Batista-da-Silva et al., submitted).

	DETERMINANTS OF MUCOSAL IMMUNITY

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
A specialized epithelial barrier lining the oral cavity, the intestinal tract, respiratory tract, and urogenital systems provides the primary protection for mucosal tissues. Breakdown of the barrier functions leads to the infiltation of bacteria or luminal noxious agents that cause inflammatory diseases, including periodontal disease in the oral cavity, inflammatory bowel diseases (IBDs) (Tlaskalova-Hogenova et al., 2004), respiratory diseases (Delclaux and Azoulay, 2003), and urogenital diseases (Connell et al., 1997; Mulvey, 2002). Physical protection is achieved by the formation of tight junctions connecting the epithelial cells, while goblet and other specialized secretory cells produce mucous enriched with antimicrobial glycoproteins, IgA class antibodies, cytokines, and chemokines to defend against the invasion of pathogens and maintain the integrity of the epithelial barrier (Mowat, 2003; Acheson and Luccioli, 2004). Another mechanical advantage of this barrier is the viscosity of the mucous secreted by the epithelial cells; this can prevent the adherence of particles or micro-organisms that are otherwise expelled by ciliary movement in the respiratory tract, or by peristalsis in the gut. Failure of these barrier functions may lead to recurrent respiratory tract infections or infestation and infection of the gut lumen, respectively.

Noxious irritation/damage of the epithelial barrier can be mediated by epithelial cells through special recognition receptors such as death Toll-like receptors, by specialized epithelial cells (microfold; M cells), or, more directly, by the penetration of bacteria or their products (Otte et al., 2003; Shi and Walker, 2004). Penetration of the epithelial barriers results in activation of resident neutrophils (polymorphonuclear leukocytes; PMNs) and macrophages; these are professional phagocytes, which provide the "immediate innate immune response" and non-specifically engulf foreign material and bacteria (Fig. 3). Cytokines and chemokines released from the injured epithelium as well as the leukocytes increase neutrophil and macrophage infiltration into the tissue, and thereby initiate the inflammatory response. Long-term residents of the subepithelial tissue, the antigen-presenting cells (APC)/dendritic cells, which are specialized macrophages, initiate the more specific "adaptive immune responses". The adaptive system is based on a specific recognition between APC and naïve T-cells, resulting in the differentiation of Th1, T-helper, and cytotoxic (NKT) T-cells, which control the immune reaction. Notably, many studies have correlated OPN expression with epithelial barrier changes (Gassler et al., 2002), with macrophage (Giachelli and Steitz, 2000; O’Regan et al., 2001; Sodek et al., 2002; Zhu et al., 2004), neutrophil (Alstergren et al., 2004), and lymphocyte activities (Ashkar et al., 2000), and with the function of reparative fibroblasts (Sodek et al., 2002).

	OPN AND THE EPITHELIAL BARRIER

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
OPN has been recognized as an important luminal regulator (Brown et al., 1992), due to its expression by epithelial cells covering luminal cavities capable of active secretion and absorption of nutrients or gasses. Indeed, earlier studies showing that epithelial cells secrete OPN first indicated that OPN is involved in controlling epithelial barrier permeability and secretory functions (Butler, 1989).

In the gastrointestinal tract, a layer of columnar epithelial cells separates the underlying mucosa from the lumen and provides a reservoir for macrophages and T- and B-lymphocytes, which are concentrated in an organized subepithelial network along the gut and can be identified in focal areas, such as the Peyer’s patches in the distal small intestine. Moreover, the epithelial layer also contains specialized cells, such as the microfold (M) cells, capable of recognizing specific bacteria and antigens and transferring them to specialized APCs that reside in the vicinity of the epithelial layer (Neurath et al., 2002; Mowat, 2003; Acheson and Luccioli, 2004). The MHC class-II and Toll-like receptors on specialized epithelial cells may be involved directly with antigen presentation to underlying CD4+ T-cells (Acheson and Luccioli, 2004) (Figs. 3, 4).

View larger version (42K): [in this window] [in a new window]   Figure 4. A diagram indicating how osteopontin may influence the adaptive immune response in mucosal tissues. Antigen taken by APC/dendritic cells and presented to naïve T-cells/CD4+ results in T-cell proliferation and differentiation into Th1 cells. The Th1 cells release IL-12, IFN-, MIF, OPN, and TNF-, which recruit macrophages for further activation of Th1 cells and promote the further recruitment of neutrophils and natural killer cells (NKT). Th2 release of IL-10 and IL-4 increases B-cell differentiation, attenuates macrophage activation, and, in conjunction with regulatory T-cells, initiates repair by myofibroblasts. Following removal of noxious agents, reduced inflammation will allow deposition of new matrix by myofibroblasts, leading to epithelial regeneration. OPN can modulate the inflammatory reaction and promote repair through its effects on T-cell differentiation and by its ability to influence the survival of epithelial cells, macrophages, and fibroblasts.

The ability of the epithelial barrier to resist stress and trauma, and to regenerate, is important for the subsequent repair of the diseased tissues. Death of epithelial cells, therefore, is an important event associated with mucosal damage and occurs through up-regulation of the Fas ligand, and in response to TGF-β1 expression and an increase in oxidative burst (Barkla and Gibson, 1999; Ophascharoensuk et al., 1999; Hagimoto et al., 2002; Kruidenier et al., 2003). In view of the role of OPN in cell survival, its presence may be important for supporting programmed cell death and preventing rapid necrotic death, which can result in intense inflammation and loss of epithelial barrier and protection.

	OPN IN MUCOSAL INFLAMMATION

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
The increased expression of OPN at sites of inflammation by epithelial, stromal, and immune cells is consistent with functions involving both the innate and adaptive pathways (Figs. 3, 4).

Innate immunity (Fig. 3) is the first line of defense for the broken epithelial barrier. IL-8 released from the injured epithelial cell recruits neutrophils and macrophages, which are capable of non-specific and specific phagocytosis—the macrophages utilizing mannose receptor or the CD14 (Toll 4) receptor for lipopolysaccharide. Upon phagocytosis, neutrophils and macrophages will continuously produce oxidative products such as hydrogen peroxide and nitric oxides. These cells, especially the macrophages, release mediators, which amplify the inflammatory reaction. The mediators include TNF-, IL-1, MCP-1, Rantes, and TGF-β1, and degradative hydrolytic enzymes responsible for connective tissue degradation, such as the matrix metalloproteinases (MMPs). Other immediate changes associated with the innate immune response occur in response to increased blood flow to the area, with a local decrease in blood velocity. This is accompanied by the expression of adhesion molecules (e.g., VCAM-1) on the endothelial cells, which increases adhesion of leukocytes and vessel permeability, thereby facilitating extravasation of leukocytes to the inflamed tissues mediated by their integrin receptors, LFA-1 and Mac-1. The effect of innate immunity on the inflammatory progression can be demonstrated in glomerulonephritis models, in which OPN expression is increased (Eddy and Giachelli, 1995; Heinzelmann et al., 1999; Kitching et al., 2002), together with the up-regulation of ICAM-1s IL-1, TGF-β1 MCP-1, and IL-8, and a decrease in IL-10 expression.

The short-lived immune response protects the injured organ prior to the development of the adaptive response (Fig. 4). The presentation of antigen by differentiated macrophages to naïve T-cells stimulates the differentiation of lymphocytes, including memory, helper, regulatory, and cytotoxic (NKT) T-cells, which augments further macrophage activity, including the clearance (phagocytosis) of apoptotic PMNs (Haslett et al., 1994). In response to IL-4, Th2 cells, in co-operation with Th1 cells, stimulate proliferation and differentiation of antibody-producing B-cells, while IL-10 secreted by Th2 cells regulates Th1 activity and thereby indirectly controls macrophage activity. During controlled infection, regulatory T-helper cells secrete IL-4 and TGF-β1, which regulate the activity of the effector lymphocytes and stimulate fibroblast proliferation required for tissue remodeling (Fig. 5). Notably, increased secretion of TGF-β1 by fibroblasts stimulates the proliferation of effector T-cells as well as antibody-secreting B-cells. In this respect, the activation of the adaptive response is more significant in mucosal defense, since mucosal tissues are challenged continuously by pathogens and noxious agents. The adaptive immune system is important in mucosal immunity, as well as in maintaining tolerance toward resident flora and nutrition products. Stimulation of lymphocyte growth and differentiation is achieved through the stimulation of the dendritic cells, which migrate to lymph-associated areas, such as the mucosal-associated lymphoid tissues (MALT; Fig. 4), and not in the infected inflamed area. Differentiated effector T-cells express selectins, which help them target the inflamed area and extravasate in a similar fashion to the PMNs. Migrating T-cells will be predominantly Th1 cells, which will stimulate further macrophage and T-cytotoxic cell activities.

View larger version (12K): [in this window] [in a new window]   Figure 5. A simple depiction of the role of OPN in the repair of submucosal connective tissues. Secreted OPN (sOPN), produced mainly by macrophages and Th1 cells, signals through CD44 and integrin receptors on fibroblasts, which differentiate into myofibroblasts. An intracellular form of iOPN associated with CD44 modulates cytoskeleton-related activities, including migration in macrophages (MØs) and fibroblasts, and both sOPN and iOPN produced by myofibroblasts (MyoFb). During the reparative phases, OPN signals through vβ3 and/or CD44 receptors to stimulate proliferation and differentiation of fibroblasts and protect them from apoptosis, thereby promoting matrix deposition and mucosal repair.

Notably, OPN may not be needed for basic activity of isolated lymphocytes or macrophages in culture, but may be required for their interaction and co-operative effects in promoting the transition from innate to adaptive responses and the initiation of repair (Fig. 5).

Neutrophils (PMNs)
Also termed granulocytes or PMNs, the neutrophils provide the immediate and non-specific line of defense for broken mucosal surfaces. The release of cytokines such as IL-8 by damaged epithelial cells recruits PMNs to sites of injury to initiate the innate defense. In some situations, mucosal immunity may involve defense through the epithelial and PMN cells only, such as in the arrest of superficial Candida infections (Steele et al., 2000; Schaller et al., 2004). PMNs which attack invading bacteria or foreign material release cytotoxic products that, unless controlled, may result in destruction of the host tissue (Jaeschke and Smith, 1997; Heinzelmann et al., 1999). The infiltration of the subepithelial tissues by PMNs is an important stage in the inflammatory process of mucosal damage in inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis (Nikolaus et al., 1998; Ina et al., 2002; Kruidenier et al., 2003; Le’Negrate et al., 2003; Kurtovic and Segal, 2004). In normal self-restricting mucosal defense processes, PMNs are usually cleared within 24 hours of injury, due to the invading macrophages, which engulf apoptotic neutrophils and arrest further neutrophil mobilization and tissue destruction (Haslett et al., 1994; Hart et al., 2000). The lack of neutrophil clearance by macrophages may result in the persistence of PMNs in inflamed tissues, which can result in increased destruction (Batista-da-Silva et al., submitted). That a similar situation is seen in TNF-null mice, in which experimental colitis is aggravated due to hyperactivation of neutrophils (Naito et al., 2003), is of particular interest, in that TNF expression is suppressed in response to DSS-induced colitis in OPN-null mice (Batista-da-Silva et al., under review).

While the release of OPN by neutrophils can contribute to the recruitment of macrophages, few studies have reported on OPN expression by neutrophils. Chitosan and G-CSF have been shown to increase OPN mRNA expression in PMNs, although the increase in the release of OPN into the medium was modest (Ueno et al., 2001). Immunocytochemical staining of OPN in PMNs (Fig. 3) confirms the presence of OPN throughout the cytoplasm and, in contrast to macrophages, shows no particular association with CD44, which is characteristically concentrated in the uropods of polarized PMNs. Also, in contrast to macrophages (Zhu et al., 2004), the cell-surface expression of CD44 is not influenced by OPN, which may reflect differences in the migratory characteristics of these cells (Alstergren et al., 2004).

Macrophages
Macrophages participate in both immediate innate and adaptive immune responses (Figs. 3, 4). Differential expression of OPN by macrophages and T-cells determines the relative levels of the immediate and delayed-type hypersensitivity responses, which are neutrophil-dependent and neutrophil-independent, respectively. In immediate responses, the macrophages are attracted and activated by cytokines secreted by neutrophils, thereby promoting a protracted inflammatory reaction that frequently results in excessive fibrosis and scar formation (Fig. 5). Macrophages, therefore, may be the most versatile cells in mucosal protection. Macrophages infiltrating the injured mucosal tissues in early stages help the PMNs phagocytose invading pathogens, while controlling the amount of damage by PMNs and attracting the more specific adaptive pathways of immune cell-mediated protection of lymphocytes. Notably, in healthy subepithelial tissues of the gut, respiratory tract, and the urogenital systems, differentiated macrophages reside for long periods as dendritic cells, which respond to noxious insults by initiating the adaptive immune response. As noted previously, not only do the macrophages/APCs in mucosal surfaces activate the adaptive immune response, but they also maintain immune tolerance toward non-pathogenic normal flora (Mowat, 2003). The cell-mediated immune response is characterized by the formation of granuloma tissue, which occurs during wound healing, and, consistent with the effects of OPN on macrophage function, granuloma formation is impaired in OPN-null mice (O’Regan et al., 1999, 2001; Ashkar et al., 2000; Morimoto et al., 2004).

Macrophages produce large amounts of OPN, which is further up-regulated by LPS stimulation (Gao et al., 2004). The OPN produced by macrophages may act as an opsonin, facilitating phagocytosis (McKee and Nanci, 1996), as well as cell adhesion, through RGD binding. While immunostaining of OPN displays a perinuclear distribution typical of secreted proteins, in migrating macrophages, OPN is also seen co-localizing with CD44 at the cell membrane of cell processes (Fig. 5) as an intracellular form of OPN (iOPN). The iOPN and its association with CD44 were originally identified in migrating fibroblasts (Zohar et al., 2000) and subsequently characterized by pulse-chase labeling studies in macrophages (Zhu et al., 2004). In the absence of OPN expression, the formation of cell processes associated with the migration of macrophages and their chemotaxis to fMLP and MCP-1, which act through G-protein-coupled receptors, are impaired. The impairment appears to be related to decreased expression of CD44 (Zhu et al., 2004), which is regulated by OPN functioning through the vβ3 integrin in macrophages (Marroquin et al., 2004) and osteoclasts (Chellaiah et al., 2003) and has been shown to be crucial for the polarization and migration of neutrophils (Alstergren et al., 2004).

In addition to its effects on macrophage recruitment and activation, MCP-1 also has important effects on OPN expression and cytokine synthesis by macrophages that affect myofibroblast accumulation in healing infarcts (Dewald et al., 2005). In macrophages stimulated with LPS and IFN-, nitric oxide (NO) directly up-regulates endogenous OPN, which acts as a negative feedback regulator of iNOS to reduce nitric oxide synthesis (Takahashi et al., 2000; Guo et al., 2001; Speyer et al., 2003). Recent studies have shown that the development of atherosclerosis is prevented by Liver X Receptor (LXR) ligands, which inhibit cytokine- and LPS-induced OPN expression in macrophages by targeting an AP1-element in the OPN promoter (Ogawa et al., 2005). Thus, expression of OPN in macrophages is required not only for recruitment, but also to orchestrate the specific adaptive and non-specific innate defense pathways.

Lymphocytes
OPN is considered to be an important lymphocyte mediator secreted by activated T-lymphocytes that induces macrophage migration and suppresses the production of reactive oxygen species, while enhancing immunoglobulin production and proliferation of B-lymphocytes (Weber et al., 1996). In the original studies of lymphocytes, OPN was identified as a T-lymphocyte activation-1 (Eta1) cytokine (Patarca et al., 1993) that was subsequently shown to be required for cell-mediated immunity and the development of the Th1 pathway and macrophage activity (Ashkar et al., 2000; Chabas et al., 2001; Jansson et al., 2002; O’Regan, 2003). The function of tissue resident macrophages/dendritic cells is not only to destroy pathogens but also to mediate the adaptive immune response by carrying pathogen antigens through the lymph circulation to peripheral lymphoid organs, where they present them to näive lymphocyte precursors through specialized MHC receptors (Fig. 4). Failure of dendritic cell activation may result in improper adaptive immune response or immune-tolerance to antigens.

Lymphocyte function in mucosal protection (Figs. 3, 4) is part of the more specific adaptive immunity. Lymphocyte activation and differentiation will usually occur via two routes:

1. Differentiation of specialized T-cells starts primarily with co-stimulation of the antigen presented by the dendritic cells through MHC-II and Toll-like receptors to naïve T-cells, but also in response to chemokines and cytokines released by dendritic cells, such as IL-12 and CC-chemokine ligand.
   
2. In the lymphoid tissue, there is a specialized macrophage population, which interacts with antigen-specific receptors of B-cells with co-stimulation of differentiated T-cells. B-cells then differentiate into their effector cells (i.e., plasma cells), proliferate, and produce antibody, mainly IgA-class immunoglobulins, which can be secreted through the epithelial barrier for mucosal defense. Most of the subepithelial lymphocytes are antibody-secreting B-cells, plasma cells, and memory T-cells. Effector T-cells, which are able to destroy infected cells and activate other cells of the immune system, are CD4+ cells, which include most of the T-helper subtypes, while some are CD8+ cells representing T killer (NKT) cells, which have a cytotoxic function and secrete IFN- to encourage killing by macrophages (Mowat et al., 2003; Watford et al., 2003; Dakic et al., 2004; Nagler-Anderson et al., 2004).
   

In CD4+ T-cells, OPN mRNA is expressed in Th1, but not in Th2, polarized cells (Nagai et al., 2001). OPN promotes adhesion of activated T-cells, and this activity is enhanced following proteolytic cleavage of OPN by thrombin (O’Regan et al., 1999). At low concentrations, OPN promotes chemotaxis but not chemokinesis of T-cells, while activated T-cell adhesion is enhanced at higher concentrations, especially following thrombin cleavage of OPN (O’Regan et al., 1999). OPN also co-stimulates T-cell proliferation and increases CD3-mediated T-cell production of IFN- and CD40 ligand (O’Regan and Berman, 2000). At low concentrations, OPN promotes chemotaxis, but not chemokinesis, of T-cells. However, this response is inhibited at higher OPN concentrations.

A variety of inflammatory and autoimmune diseases—including multiple sclerosis, rheumatoid arthritis, and atherosclerosis—is critically regulated by NKT cells, which also secrete OPN. The OPN augments NKT cell activation and triggers neutrophil infiltration and activation. Consistent with this role of OPN in NKT cell function, OPN-null mice, similar to NKT cell-deficient mice, are refractory to Con A-induced hepatitis. However, a neutralizing antibody, specific for a cryptic integrin-binding epitope of OPN that is exposed by thrombin cleavage, ameliorates the development of hepatitis in normal mice (Diao et al., 2004). In contrast, over-expression of OPN in the liver of transgenic mice resulted in massive liver necrosis and monocyte infiltration, due to an imbalance of the Th1 and Th2 immune responses (Mimura et al., 2004), presumably caused by the attraction of macrophage precursors by OPN and its promotion of the Th1 response.

Impaired OPN–/– macrophage differentiation and functions (Weber et al., 2002; Zhu et al., 2004) may be responsible for deficient healing in OPN-null mice (Liaw et al., 1998; Rittling et al., 1998). OPN induces T-cell proliferation, adhesion, and chemotaxis, especially in relation to granulomatous lesions (O’Regan et al., 1999). Moreover, soluble OPN may modulate the differentiation and proliferation of CD4+ and CD8+ lymphocytes (Higuchi et al., 2004). Over-expression of OPN in transgenic mice increased the numbers of CD4+ T-cells, but not CD8+ T-cells, in the spleen, particularly in the lymph nodes. Skin sensitization with 2,4-dinitrofluorobenzene (DNFB) in these mice increased the number of CD4+ cells and recruitment of CD8+ cells. However, peritoneal sensitization with DNFB (Higuchi et al., 2004) resulted in increases in the numbers of CD8+ T-cells in the peritoneal exudate, with no difference in the numbers of CD4+ T-cells. These results suggest that different responses might be anticipated in mucosal immunity, where there is an epithelial barrier involvement in the transfer of the inflammatory signals. In this regard, studies of colitis in OPN-null mice support the suppression of CD4+ and CD8+ cell numbers of the inflamed OPN-null spleens (Batista-da-Silva et al., submitted). These observations also suggest a direct effect of OPN on T-cells, or, alternatively, indirect effects due to lack of functional macrophages or differentiated dendritic cell stimulation. This is accompanied by a decrease of IL-12, IFN-, and the oxidative burst necessary for the development of proper protective inflammatory reaction.

IFN- treatment of Th-1 cells has been shown to induce OPN mRNA and protein expression in a time-dependent and dose-dependent manner (Li et al., 2003), consistent with the contribution of OPN to Th1 activation. These effects may also be dependent on the ability of macrophages to differentiate into dendritic cells necessary for the T-cellular response (Weiss et al., 2001) and their mobilization from the regional lymph nodes. Up-regulation of CD40L by OPN in T-lymphocytes (O’Regan and Berman, 2000) provides mechanistic support for the association of OPN with polyclonal B-cell proliferation and humoral autoimmune disease (Weber et al., 1996). During stimulation of the lymphoid centers, specific dendritic cells, through interaction with CD4 (naïve) lymphocytes, present antigen to B-cells, which have antigen-specific receptors that enable them to internalize large amounts of specific antigens, proliferate, and produce specific antibodies. Interestingly, an important mechanism for IgA production is that promoted by Th3 secreted TGF-β1, which controls IgA switching and secretion in vivo (Borsutzky et al., 2004). B-cells then migrate into the surrounding mucosa and release secretory IgA through the epithelial lining of the mucosa. The secretory IgA binds directly to pathogens and prevents their attachment to epithelial cells; it also coats antigens, promoting their engulfment by macrophages. Although it is unclear how TGF-β1 and its associated receptors control B-cell activity, the Toll death receptors and G-protein-coupled receptors appear to be involved (Cazac and Roes, 2000; Roes et al., 2003).

TGF-β1 and OPN are important mediators of extracellular matrix formation and wound healing (Bendeck et al., 2000; Sodek et al., 2000; Denhardt et al., 2001a,b), and the matrix-promoting and immunoregulatory activities of TGF-β1 have been studied quite extensively (Kitani et al., 2003; Wahl and Chen, 2003). However, the role of OPN and its relation to TGF-β1-mediated activities are largely unknown. TGF-β1 modulates differentiation of naïve CD4 lymphocytes (Wang and Mosmann, 2001), and over-expression of TGF-β1 reduces the susceptibility of mice to colitis by blunting Th3 immune and humoral responses (Egger et al., 1998). TGF-β1 expression during inflammation and immune reactions also stimulates IL-10 secretion in Th1 cells, regulates T-lymphocyte activity, and induces OPN expression in immune as well as reparative fibroblasts (Overall et al., 1991) (Fig. 5).

	OPN AND THE INITIATION OF HEALING

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
Monocytes/macrophages, lymphocytes, and mast cells recruited to the submucosa produce the cytokines and growth factors necessary for fibroblast proliferation and neo-vascularization, as part of granulation tissue formation (Orlando, 2002). Activated macrophages are responsible for the oxidative burst and for IL-10 secretion—processes that up-regulate fibroblast proliferation and differentiation into myofibroblasts (McKaig et al., 2002) through the production of TGF-β1 (di Mola et al., 1999; McKaig et al., 2002). Connective tissue remodeling occurs around the ulcerated epithelium with the formation of granulation tissue. Matrix metalloproteinases (MMPs) derived from macrophages and from the activated fibroblasts (Vaalamo et al., 1998; Pirila et al., 2003) augment matrix remodeling and overall tissue destruction (Fig. 5). OPN has also been reported to activate MMP-3 (Fedarko et al., 2000), the expression of which is increased markedly in inflamed colons of patients with ulcerative colitis and Crohn’s disease, and correlates with the loss of mucosal integrity, suggesting an important role for stromelysin and its possible activation by OPN in the process of destruction and tissue remodeling in inflammatory bowel diseases (Heuschkel et al., 2000; von Lampe et al., 2000). Myofibroblasts, which are typically associated with reparative granulation tissue formation (Desmoulière, 1995; Neubauer et al., 2001), are characterized by an enhanced expression of -smooth muscle actin (-SMA) in stress fibers (Jelaska and Korn, 2000; Thibault et al., 2001; Tomasek et al., 2002; McKaig et al., 2003). During matrix formation, myofibroblasts respond to TGF-β1 by increased expression of extracellular matrix (ECM), including collagen, and selective suppression of MMPs (Overall et al., 1991). Since TGF-β1 also increases -SMA, it is conceivable that the myofibroblast phenotype induced in fibroblasts is mediated through the up-regulation of TGF-β1, which also increases the expression of OPN, integrins, and -actinin (Kawano et al., 2000; Mazzali et al., 2002) and promotes integrin-mediated collagen gel contraction (McKaig et al., 2003). TGF-β1 and OPN also down-regulate apoptosis of fibroblasts and thus increase matrix deposition (Desmoulière, 1995; Jelaska and Korn, 2000; Zohar et al., 2004). Indeed, connective tissue wound healing and fibrosis, subsequent to inflammatory disease, are impaired in OPN-null mice (Liaw et al., 1998; Trueblood et al., 2001).

That OPN is expressed by epithelial and mucosal cells, as well as by immune cells in the intestines, has been shown (Qu and Dvorak, 1997; Gassler et al., 2002). However, despite the perceived importance of OPN in cell-mediated immune responses and wound healing, there have been few studies of OPN in the normal or diseased intestine. In support of the proposed functions of OPN in protecting the intestine from pathogens and in the development of inflammatory bowel diseases (Masuda et al., 2003), our preliminary studies indicate that destruction of the intestinal tissues is exacerbated in OPN-null mice subjected to experimental colitis (Batista-da-Silva et al., submitted). The loss of mucosal integrity and inflammatory destruction as seen in patients with ulcerative colitis and Crohn’s disease correlates with the production of IL-1β, IL-6, TNF-, IL-10, TGF-β1, and activated MMPs (Fedarko et al., 2000; Heuschkel et al., 2000; von Lampe et al., 2000; McKaig et al., 2003). Impairment of these mediators’ activity and overall granulation tissue formation will alter the process of tissue remodeling and repair in inflammatory bowel diseases.

	SUMMARY

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 
The multi-functional role of OPN in inflammatory diseases is now well-established. However, elucidating these functions is complicated by the temporo-spatial expression of different forms of OPN by inflammatory cells and reparative fibroblasts, as the different immune system pathways respond in conjunction with reparative cells to protect and repair damaged tissues. In mucosal disease, further complexity is introduced by the expression of OPN by most of the sub-mucosal cells, including epithelial, immune cells, and fibroblasts, all of which contribute to the barrier function, immunity, and repair processes. Given the pivotal role of OPN in mucosal protection, identifying the specific functions of the different signaling motifs in the context of the different isoforms of OPN remains a challenge in ongoing studies of mucosal diseases.

	ACKNOWLEDGMENTS

 
This work was funded by grants MOP-36333 and MOP-457134 from the Canadian Institutes of Health Research to JS and RZ, and by a Sick Children Foundation grant to RZ.

Received for publication March 31, 2005. Accepted for publication November 8, 2005.

	REFERENCES

TOP ABSTRACT INTRODUCTION OPN STRUCTURE AND RELATED... OPN AND INFLAMMATORY DISEASES DETERMINANTS OF MUCOSAL IMMUNITY OPN AND THE EPITHELIAL... OPN IN MUCOSAL INFLAMMATION OPN AND THE INITIATION... SUMMARY REFERENCES

 

• Aarbiou J, Verhoosel RM, Van Wetering S, De Boer WI, Van Krieken JH, Litvinov SV, et al. (2004). Neutrophil defensins enhance lung epithelial wound closure and mucin gene expression in vitro. Am J Respir Cell Mol Biol 30:193–201.[Abstract/Free Full Text]
• Acheson DW, Luccioli S (2004). Microbial-gut interactions in health and disease. Mucosal immune responses. Best Pract Res Clin Gastroenterol 18:387–404.[CrossRef][Medline] [Order article via Infotrieve]
• Alstergren P, Zhu B, Glogauer M, Mak T, Ellen R, Sodek J (2004). Polarization and directed migration of murine neutrophils is dependent on cell-surface expression of CD44. J Cell Immunol 231:146–157.
• Ashkar S, Weber GF, Panoutsakopoulou V, Sanchirico ME, Jansson M, Zawaideh S, et al. (2000). Eta-1 (osteopontin): an early component of type-1 (cell-mediated) immunity. Science 287:860–864.[Abstract/Free Full Text]
• Barkla DH, Gibson PR (1999). The fate of epithelial cells in the human large intestine. Pathology 31:230–238.[CrossRef][Medline] [Order article via Infotrieve]
• Basu S, Fenton MJ (2004). Toll-like receptors: function and roles in lung disease. Am J Physiol Lung Cell Mol Physiol 286:L887–L892.[Abstract/Free Full Text]
• Batista-Da-Silva AP, Pollett A, Rittling SR, Denhardt DT, Sodek J, Zohar R (2005). Impaired inflammatory response and increased tissue destruction in the absence of osteopontin (OPN) in a murine model of inflammatory colitis. J Cell Physiol (under review).
• Bayless KJ, Meininger GA, Scholtz JM, Davis GE (1998). Osteopontin is a ligand for the alpha4beta1 integrin. J Cell Sci 111(Pt 9):1165–1174.[Abstract]
• Bendeck MP, Irvin C, Reidy M, Smith L, Mulholland D, Horton M, et al. (2000). Smooth muscle cell matrix metalloproteinase production is stimulated via alpha(v)beta(3) integrin. Arterioscler Thromb Vasc Biol 20:1467–1472.[Abstract/Free Full Text]
• Blom T, Franzen A, Heinegard D, Holmdahl R (2003). Comment on "The influence of the proinflammatory cytokine, osteopontin, on autoimmune demyelinating disease". Science 299(5614):1845; author reply 1845.[Medline] [Order article via Infotrieve]
• Borsutzky S, Cazac BB, Roes J, Guzman CA (2004). TGF-beta receptor signaling is critical for mucosal IgA responses. J Immunol 173:3305–3309.[Abstract/Free Full Text]
• Brown LF, Berse B, Van de Water L, Papadopoulos-Sergiou L, Perruzzi CA, Manseau EJ, et al. (1992). Expression and distribution of osteopontin in human tissues: widespread association with luminal epithelial surfaces. Mol Biol Cell 3:1169–1180.[Abstract]
• Butler WT (1989). The nature and significance of osteopontin. Connect Tissue Res 23:123–136.[Medline] [Order article via Infotrieve]
• Cazac BB, Roes J (2000). TGF-beta receptor controls B cell responsiveness and induction of IgA in vivo. Immunity 13:443–451.[CrossRef][Medline] [Order article via Infotrieve]
• Chabas D, Baranzini SE, Mitchell D, Bernard CC, Rittling SR, Denhardt DT, et al. (2001). The influence of the proinflammatory cytokine, osteopontin, on autoimmune demyelinating disease. Science 294:1731–1735.[Abstract/Free Full Text]
• Chellaiah MA, Kizer N, Biswas R, Alvarez U, Strauss-Schoenberger J, Rifas L, et al. (2003). Osteopontin deficiency produces osteoclast dysfunction due to reduced CD44 surface expression. Mol Biol Cell 14:173–189.[Abstract/Free Full Text]
• Christensen B, Nielsen MS, Haselmann KF, Petersen TE, Sorensen ES (2005). Post-translationally modified residues of native human osteopontin are located in clusters. Identification of 36 phosphorylation and five O-glycosylation sites and their biological implications. Biochem J 390(Pt 1):285–292.[CrossRef][Medline] [Order article via Infotrieve]
• Connell H, Hedlund M, Agace A, Svanborg C (1997). Bacterial attachment to uro-epithelial cells: mechanisms and consequences. Adv Dent Res 11:50–58.[Abstract/Free Full Text]
• Craig AM, Nemir M, Mukherjee BB, Chambers AF, Denhardt DT (1988). Identification of the major phosphoprotein secreted by many rodent cell lines as 2ar/osteopontin: enhanced expression in H-ras-transformed 3T3 cells. Biochem Biophys Res Commun 157:166–173.[CrossRef][Medline] [Order article via Infotrieve]
• Craig-Mylius K, Weber GF, Coburn J, Glickstein L (2005). Borrelia burgdorferi, an extracellular pathogen, circumvents osteopontin in inducing an inflammatory cytokine response. J Leukoc Biol 77:710–718.[Abstract/Free Full Text]
• Dakic A, Shao QX, D’Amico A, O’Keeffe M, Chen WF, Shortman K, et al. (2004). Development of the dendritic cell system during mouse ontogeny. J Immunol 172:1018–1027.[Abstract/Free Full Text]
• Debard N, Sierro F, Browning J, Kraehenbuhl JP (2001). Effect of mature lymphocytes and lymphotoxin on the development of the follicle-associated epithelium and M cells in mouse Peyer’s patches. Gastroenterology 120:1173–1182.
• Delclaux C, Azoulay E (2003). Inflammatory response to infectious pulmonary injury. Eur Respir J Suppl 42:10s–14s.[Medline] [Order article via Infotrieve]
• Denhardt DT, Lopez CA, Rollo EE, Hwang SM, An XR, Walther SE (1995). Osteopontin-induced modifications of cellular functions. Ann NY Acad Sci 760:127–142.[Medline] [Order article via Infotrieve]
• Denhardt DT, Noda M, O’Regan AW, Pavlin D, Berman JS (2001a). Osteopontin as a means to cope with environmental insults: regulation of inflammation, tissue remodeling, and cell survival. J Clin Invest 107:1055–1061.[Medline] [Order article via Infotrieve]
• Denhardt DT, Giachelli CM, Rittling SR (2001b). Role of osteopontin in cellular signaling and toxicant injury. Annu Rev Pharmacol Toxicol 41:723–749.[CrossRef][Medline] [Order article via Infotrieve]
• Desmoulière A (1995). Factors influencing myofibroblast differentiation during wound healing and fibrosis. Cell Biol Int 19:471–476.[CrossRef][Medline] [Order article via Infotrieve]
• Dewald O, Zymek P, Winkelmann K, Koerting A, Ren G, Abou-Khamis T, et al. (2005). CCL2/monocyte chemoattractant protein-1 regulates inflammatory responses critical to healing myocardial infarcts. Circ Res 96:881–889.[Abstract/Free Full Text]
• di Mola FF, Friess H, Scheuren A, Di Sebastiano P, Graber H, Egger B, et al. (1999). Transforming growth factor-betas and their signaling receptors are coexpressed in Crohn’s disease. Ann Surg 229:67–75.[CrossRef][Medline] [Order article via Infotrieve]
• Diao H, Kon S, Iwabuchi K, Kimura C, Morimoto J, Ito D, et al. (2004). Osteopontin as a mediator of NKT cell function in T cell-mediated liver diseases. Immunity 21:539–550.[CrossRef][Medline] [Order article via Infotrieve]
• Eddy AA, Giachelli CM (1995). Renal expression of genes that promote interstitial inflammation and fibrosis in rats with protein-overload proteinuria. Kidney Int 47:1546–1557.[Medline] [Order article via Infotrieve]
• Egger B, Carey HV, Procaccino F, Chai NN, Sandgren EP, Lakshmanan J, et al. (1998). Reduced susceptibility of mice overexpressing transforming growth factor alpha to dextran sodium sulphate induced colitis. Gut 43:64–70.[Abstract/Free Full Text]
• Fedarko NS, Fohr B, Robey PG, Young MG, Fisher LW (2000). Factor H binding to bone sialoprotein and osteopontin enables tumor cell evasion of complement-mediated attack. J Biol Chem 275:16666–16672.[Abstract/Free Full Text]
• Fisher LW, Fedarko NS (2003). Six genes expressed in bones and teeth encode the current members of the SIBLING family of proteins. Connect Tissue Res 44(Suppl 1):33–40.[Medline] [Order article via Infotrieve]
• Gao C, Guo H, Wei J, Mi Z, Wai P, Kuo PC (2004). S-nitrosylation of heterogeneous nuclear ribonucleoprotein A/B regulates osteopontin transcription in endotoxin-stimulated murine macrophages. J Biol Chem 279:11236–11243. Epub 2004 Jan 13.[Abstract/Free Full Text]
• Gassler N, Autschbach F, Gauer S, Bohn J, Sido B, Otto HF, et al. (2002). Expression of osteopontin (Eta-1) in Crohn disease of the terminal ileum. Scand J Gastroenterol 37:1286–1295.[CrossRef][Medline] [Order article via Infotrieve]
• Giachelli CM, Steitz S (2000). Osteopontin: a versatile regulator of inflammation and biomineralization. Matrix Biol 19:615–622.[CrossRef][Medline] [Order article via Infotrieve]
• Giachelli CM, Lombardi D, Johnson RJ, Murry CE, Almeida M (1998). Evidence for a role of osteopontin in macrophage infiltration in response to pathological stimuli in vivo. Am J Pathol 152:353–358.[Abstract]
• Guo H, Cai CQ, Schroeder RA, Kuo PC (2001). Osteopontin is a negative feedback regulator of nitric oxide synthesis in murine macrophages. J Immunol 166:1079–1086.[Abstract/Free Full Text]
• Hagimoto N, Kuwano K, Inoshima I, Yoshimi M, Nakamura N, Fujita M, et al. (2002). TGF-beta 1 as an enhancer of Fas-mediated apoptosis of lung epithelial cells. J Immunol 168:6470–6478.[Abstract/Free Full Text]
• Hart SP, Ross JA, Ross K, Haslett D, Dransfield I (2000). Molecular characterization of the surface of apoptotic neutrophils: implications for functional downregulation and recognition by phagocytes. Cell Death Differ 7:493–503.[CrossRef][Medline] [Order article via Infotrieve]
• Haslett C, Savill JS, Whyte MK, Stern M, Dransfield I, Meagher LC (1994). Granulocyte apoptosis and the control of inflammation. Philos Trans R Soc Lond B Biol Sci 345:327–333.[Abstract/Free Full Text]
• Heinzelmann M, Mercer-Jones MA, Passmore JC (1999). Neutrophils and renal failure. Am J Kidney Dis 34:384–399.[Medline] [Order article via Infotrieve]
• Heuschkel RB, MacDonald TT, Monteleone G, Bajaj-Elliott M, Smith JA, Pender SL (2000). Imbalance of stromelysin-1 and TIMP-1 in the mucosal lesions of children with inflammatory bowel disease. Gut 47:57–62.[Abstract/Free Full Text]
• Higuchi Y, Tamura Y, Uchida T, Matsuura K, Hijiya N, Yamamoto S (2004). The roles of soluble osteopontin using osteopontin-transgenic mice in vivo: proliferation of CD4+ T lymphocytes and the enhancement of cell-mediated immune responses. Pathobiology 71:1–11.[Medline] [Order article via Infotrieve]
• Ide M, Yamate J, Machida Y, Nakanishi M, Kuwamura M, Kotani T, et al. (2003). Emergence of different macrophage populations in hepatic fibrosis following thioacetamide-induced acute hepatocyte injury in rats. J Comp Pathol 128:41–51.[CrossRef][Medline] [Order article via Infotrieve]
• Ina K, Itoh J, Fukushima K, Kusugami K, Yamaguchi T, Kyokane K, et al. (1999). Resistance of Crohn’s disease T cells to multiple apoptotic signals is associated with a Bcl-2/Bax mucosal imbalance. J Immunol 163:1081–1090.[Abstract/Free Full Text]
• Ina K, Kusugami K, Shimada M, Tsuzuki T, Nishio Y, Binion DG, et al. (2002). Suppressive effects of cyclosporine A on neutrophils and T cells may be related to therapeutic benefits in patients with steroid-resistant ulcerative colitis. Inflamm Bowel Dis 8:1–9.[Medline] [Order article via Infotrieve]
• Iwasaki A, Medzhitov R (2004). Toll-like receptor control of the adaptive immune responses. Nat Immunol 5:987–995.[CrossRef][Medline] [Order article via Infotrieve]
• Jacobs JP, Pettit AR, Shinohara ML, Jansson M, Cantor H, Gravallese EM, et al. (2004). Lack of requirement of osteopontin for inflammation, bone erosion, and cartilage damage in the K/BxN model of autoantibody-mediated arthritis. Arthritis Rheum 50:2685–2694.[CrossRef][Medline] [Order article via Infotrieve]
• Jaeschke H, Smith CW (1997). Mechanisms of neutrophil-induced parenchymal cell injury. J Leukoc Biol 61:647–653.[Abstract]
• Jander S, Bussini S, Neuen-Jacob E, Bosse F, Menge T, Muller HW, et al. (2002). Osteopontin: a novel axon-regulated Schwann cell gene. J Neurosci Res 67:156–166.[Medline] [Order article via Infotrieve]
• Jansson M, Panoutsakopoulou V, Baker J, Klein L, Cantor H (2002). Cutting edge: attenuated experimental autoimmune encephalomyelitis in eta-1/osteopontin-deficient mice. J Immunol 168:2096–2099.[Abstract/Free Full Text]
• Jelaska A, Korn JH (2000). Role of apoptosis and transforming growth factor beta1 in fibroblast selection and activation in systemic sclerosis. Arthritis Rheum 43:2230–2239.[CrossRef][Medline] [Order article via Infotrieve]
• Katagiri YU, Sleeman J, Fujii H, Herrlich P, Hotta H, Tanaka K, et al. (1999). CD44 variants but not CD44s cooperate with beta1-containing integrins to permit cells to bind to osteopontin independently of arginine-glycine-aspartic acid, thereby stimulating cell motility and chemotaxis. Cancer Res 59:219–226.[Abstract/Free Full Text]
• Kawano H, Cody RJ, Graf K, Goetze S, Kawano Y, Schnee J, et al. (2000). Angiotensin II enhances integrin and alpha-actinin expression in adult rat cardiac fibroblasts. Hypertension 35(1 Pt 2):273–279.[Abstract/Free Full Text]
• Kitani A, Fuss I, Nakamura K, Kumaki F, Usui T, Strober W (2003). Transforming growth factor (TGF)-beta1-producing regulatory T cells induce Smad-mediated interleukin 10 secretion that facilitates coordinated immunoregulatory activity and amelioration of TGF-beta1-mediated fibrosis. J Exp Med 198:1179–1188.[Abstract/Free Full Text]
• Kitching AR, Katerelos M, Mudge SJ, Tipping PG, Power DA, Holdsworth SR (2002). Interleukin-10 inhibits experimental mesangial proliferative glomerulonephritis. Clin Exp Immunol 128:36–43.[CrossRef][Medline] [Order article via Infotrieve]
• Koguchi Y, Kawakami K, Uezu K, Fukushima K, Kon S, Maeda M, et al. (2003). High plasma osteopontin level and its relationship with interleukin-12-mediated type 1 T helper cell response in tuberculosis. Am J Respir Crit Care Med 167:1355–1359.[Abstract/Free Full Text]
• Kruidenier L, Kuiper I, Lamers CB, Verspaget HW (2003). Intestinal oxidative damage in inflammatory bowel disease: semi-quantification, localization, and association with mucosal antioxidants. J Pathol 201:28–36.[CrossRef][Medline] [Order article via Infotrieve]
• Kurtovic J, Segal I (2004). Recent advances in biological therapy for inflammatory bowel disease. Trop Gastroenterol 25:9–14.[Medline] [Order article via Infotrieve]
• Lampe MA, Patarca R, Iregui MV, Cantor H (1991). Polyclonal B cell activation by the Eta-1 cytokine and the development of systemic autoimmune disease. J Immunol 147:2902–2906.[Abstract]
• Le’Negrate G, Rostagno P, Auberger P, Rossi B, Hofman P (2003). Downregulation of caspases and Fas ligand expression, and increased lifespan of neutrophils after transmigration across intestinal epithelium. Cell Death Differ 10:153–162.[CrossRef][Medline] [Order article via Infotrieve]
• Leali D, Dell’Era P, Stabile H, Sennino B, Chambers AF, Naldini A, et al. (2003). Osteopontin (Eta-1) and fibroblast growth factor-2 cross-talk in angiogenesis. J Immunol 171:1085–1093.[Abstract/Free Full Text]
• Lekic PC, Rajshankar D, Chen H, Tenenbaum H, McCulloch CA (2001). Transplantation of labeled periodontal ligament cells promotes regeneration of alveolar bone. Anat Rec 262:193–202.[CrossRef][Medline] [Order article via Infotrieve]
• Li X, O’Regan AW, Berman JS (2003). IFN-gamma induction of osteopontin expression in human monocytoid cells. J Interferon Cytokine Res 23:259–265.[CrossRef][Medline] [Order article via Infotrieve]
• Liaw L, Birk DE, Ballas CB, Whitsitt JS, Davidson JM, Hogan BL (1998). Altered wound healing in mice lacking a functional osteopontin gene (spp1). J Clin Invest 101:1468–1478.[Medline] [Order article via Infotrieve]
• Lin YH, Yang-Yen HF (2001). The osteopontin-CD44 survival signal involves activation of the phosphatidylinositol 3-kinase/Akt signaling pathway. J Biol Chem 276:46024–46030.[Abstract/Free Full Text]
• Marroquin CE, Downey L, Guo H, Kuo PC (2004). Osteopontin increases CD44 expression and cell adhesion in RAW 264.7 murine leukemia cells. Immunol Lett 95:109–112.[CrossRef][Medline] [Order article via Infotrieve]
• Masuda H, Takahashi Y, Asai S, Takayama T (2003). Distinct gene expression of osteopontin in patients with ulcerative colitis. J Surg Res 111:85–90.[CrossRef][Medline] [Order article via Infotrieve]
• Mazzali M, Hughes J, Dantas M, Liaw L, Steitz S, Alpers CE, et al. (2002). Effects of cyclosporine in osteopontin null mice. Kidney Int 62:78–85.[CrossRef][Medline] [Order article via Infotrieve]
• McKaig BC, Hughes K, Tighe PJ, Mahida YR (2002). Differential expression of TGF-beta isoforms by normal and inflammatory bowel disease intestinal myofibroblasts. Am J Physiol Cell Physiol 282:C172–C182.[Abstract/Free Full Text]
• McKaig BC, McWilliams D, Watson SA, Mahida YR, Brannigan AE, Watson RW, et al. (2003). Expression and regulation of tissue inhibitor of metalloproteinase-1 and matrix metalloproteinases by intestinal myofibroblasts in inflammatory bowel disease. Am J Pathol 162:1355–1360.[Abstract/Free Full Text]
• McKee MD, Nanci A (1996). Secretion of osteopontin by macrophages and its accumulation at tissue surfaces during wound healing in mineralized tissues: a potential requirement for macrophage adhesion and phagocytosis. Anat Rec 245:394–409.[CrossRef][Medline] [Order article via Infotrieve]
• Mimura S, Mochida S, Inao M, Matsui A, Nagoshi S, Yoshimoto T, et al. (2004). Massive liver necrosis after provocation of imbalance between Th1 and Th2 immune reactions in osteopontin transgenic mice. J Gastroenterol 39:867–872.[CrossRef][Medline] [Order article via Infotrieve]
• Miyazaki Y, Tashiro T, Higuchi Y, Setoguchi M, Yamamoto S, Nagai H, et al. (1995). Expression of osteopontin in a macrophage cell line and in transgenic mice with pulmonary fibrosis resulting from the lung expression of a tumor necrosis factor-alpha transgene. Ann NY Acad Sci 760:334–341.[CrossRef][Medline] [Order article via Infotrieve]
• Morimoto J, Inobe M, Kimura C, Kon S, Diao H, Aoki M, et al. (2004). Osteopontin affects the persistence of beta-glucan-induced hepatic granuloma formation and tissue injury through two distinct mechanisms. Int Immunol 16:477–488.[Abstract/Free Full Text]
• Mowat AM (2003). Anatomical basis of tolerance and immunity to intestinal antigens. Nat Rev Immunol 3:331–341.[CrossRef][Medline] [Order article via Infotrieve]
• Mowat AM, Donachie AM, Parker LA, Robson NC, Beacock-Sharp H, McIntyre LJ, et al. (2003). The role of dendritic cells in regulating mucosal immunity and tolerance. Novartis Found Symp 252:291–302; discussion 302–305.[Medline] [Order article via Infotrieve]
• Mulvey MA (2002). Adhesion and entry of uropathogenic Escherichia coli. Cell Microbiol 4:257–271.[CrossRef][Medline] [Order article via Infotrieve]
• Nagai S, Hashimoto S, Yamashita T, Toyoda N, Satoh T, Suzuki T, et al. (2001). Comprehensive gene expression profile of human activated T(h)1- and T(h)2-polarized cells. Int Immunol 13:367–376.[Abstract/Free Full Text]
• Nagata T, Todescan R, Goldberg HA, Zhang Q, Sodek J (1989). Sulphation of secreted phosphoprotein I (SPPI, osteopontin) is associated with mineralized tissue formation. Biochem Biophys Res Commun 165:234–240.[CrossRef][Medline] [Order article via Infotrieve]
• Nagler-Anderson C, Bhan AK, Podolsky DK, Terhorst C (2004). Control freaks: immune regulatory cells. Nat Immunol 5:119–122.[CrossRef][Medline] [Order article via Infotrieve]
• Naito Y, Takagi T, Handa O, Ishikawa T, Nakagawa S, Yamaguchi T, et al. (2003). Enhanced intestinal inflammation induced by dextran sulfate sodium in tumor necrosis factor-alpha deficient mice. J Gastroenterol Hepatol 18:560–569.[CrossRef][Medline] [Order article via Infotrieve]
• Nau GJ, Liaw L, Chupp GL, Berman JS, Hogan BL, Young RA (1999). Attenuated host resistance against Mycobacterium bovis BCG infection in mice lacking osteopontin. Infect Immun 67:4223–4230.[Abstract/Free Full Text]
• Neubauer K, Saile B, Ramadori G (2001). Liver fibrosis and altered matrix synthesis. Can J Gastroenterol 15:187–193.[Medline] [Order article via Infotrieve]
• Neurath MF, Finotto S, Glimcher LH (2002). The role of Th1/Th2 polarization in mucosal immunity. Nat Med 8:567–573.[CrossRef][Medline] [Order article via Infotrieve]
• Nikolaus S, Bauditz J, Gionchetti P, Witt C, Lochs H, Schreiber S (1998). Increased secretion of pro-inflammatory cytokines by circulating polymorphonuclear neutrophils and regulation by interleukin 10 during intestinal inflammation. Gut 42:470–476.[Abstract/Free Full Text]
• Noiri E, Dickman K, Miller F, Romanov G, Romanov VI, Shaw R, et al. (1999). Reduced tolerance to acute renal ischemia in mice with a targeted disruption of the osteopontin gene. Kidney Int 56:74–82.[CrossRef][Medline] [Order article via Infotrieve]
• O’Regan A (2003). The role of osteopontin in lung disease. Cytokine Growth Factor Rev 14:479–488.[CrossRef][Medline] [Order article via Infotrieve]
• O’Regan A, Berman JS (2000). Osteopontin: a key cytokine in cell-mediated and granulomatous inflammation. Int J Exp Pathol 81:373–390.[CrossRef][Medline] [Order article via Infotrieve]
• O’Regan AW, Chupp GL, Lowry JA, Goetschkes M, Mulligan N, Berman JS (1999). Osteopontin is associated with T cells in sarcoid granulomas and has T cell adhesive and cytokine-like properties in vitro. J Immunol 162:1024–1031.[Abstract/Free Full Text]
• O’Regan AW, Hayden JM, Body S, Liaw L, Mulligan N, Goetschkes M, et al. (2001). Abnormal pulmonary granuloma formation in osteopontin-deficient mice. Am J Respir Crit Care Med 164:2243–2247.[Abstract/Free Full Text]
• Ogawa D, Stone JF, Takata Y, Blaschke F, Chu VH, Towler DA, et al. (2005). Liver X receptor agonists inhibit cytokine-induced osteopontin expression in macrophages through interference with activator protein-1 signaling pathways. Circ Res 96:59–67.[CrossRef]
• Ohshima S, Kobayashi H, Yamaguchi N, Nishioka K, Umeshita-Sasai M, Mima T, et al. (2002a). Expression of osteopontin at sites of bone erosion in a murine experimental arthritis model of collagen-induced arthritis: possible involvement of osteopontin in bone destruction in arthritis. Arthritis Rheum 46:1094–1101.[CrossRef][Medline] [Order article via Infotrieve]
• Ohshima S, Yamaguchi N, Nishioka K, Mima T, Ishii T, Umeshita-Sasai M, et al. (2002b). Enhanced local production of osteopontin in rheumatoid joints. J Rheumatol 29:2061–2067.[Abstract/Free Full Text]
• Okada H, Moriwaki K, Konishi K, Kobayashi T, Sugahara S, Nakamoto H, et al. (2000). Tubular osteopontin expression in human glomerulonephritis and renal vasculitis. Am J Kidney Dis 36:498–506.[Medline] [Order article via Infotrieve]
• Ophascharoensuk V, Giachelli CM, Gordon K, Hughes J, Pichler R, Brown P, et al. (1999). Obstructive uropathy in the mouse: role of osteopontin in interstitial fibrosis and apoptosis. Kidney Int 56:571–580.[CrossRef][Medline] [Order article via Infotrieve]
• Orlando RC (2002). Mechanisms of epithelial injury and inflammation in gastrointestinal diseases. Rev Gastroenterol Disord 2(Suppl 2): S2–S8.
• Otte JM, Rosenberg IM, Podolsky DK (2003). Intestinal myofibroblasts in innate immune responses of the intestine. Gastroenterology 124:1866–1878.[CrossRef][Medline] [Order article via Infotrieve]
• Overall CM, Wrana JL, Sodek J (1991). Transcriptional and post-transcriptional regulation of 72-kDa gelatinase/type IV collagenase by transforming growth factor-beta 1 in human fibroblasts. Comparisons with collagenase and tissue inhibitor of matrix metalloproteinase gene expression. J Biol Chem 266:14064–14071.[Abstract/Free Full Text]
• Paleolog E (2003). The therapeutic potential of TNF-alpha blockade in rheumatoid arthritis. Expert Opin Investig Drugs 12:1087–1095.[Medline] [Order article via Infotrieve]
• Patarca R, Freeman GJ, Singh RP, Wei FY, Durfee T, Blattner F, et al. (1989). Structural and functional studies of the early T lymphocyte activation 1 (Eta-1) gene. Definition of a novel T cell-dependent response associated with genetic resistance to bacterial infection. J Exp Med 170:145–161.[Abstract/Free Full Text]
• Patarca R, Saavedra RA, Cantor H (1993). Molecular and cellular basis of genetic resistance to bacterial infection: the role of the early T-lymphocyte activation-1/osteopontin gene. Crit Rev Immunol 13:225–246.[Medline] [Order article via Infotrieve]
• Pirila E, Ramamurthy NS, Sorsa T, Salo T, Hietanen J, Maisi P (2003). Gelatinase A (MMP-2), collagenase-2 (MMP-8), and laminin-5 gamma2-chain expression in murine inflammatory bowel disease (ulcerative colitis). Dig Dis Sci 48:93–98.[CrossRef][Medline] [Order article via Infotrieve]
• Prince CW, Butler WT (1987). 1,25-Dihydroxyvitamin D3 regulates the biosynthesis of osteopontin, a bone-derived cell attachment protein, in clonal osteoblast-like osteosarcoma cells. Coll Relat Res 7:305–313.[Medline] [Order article via Infotrieve]
• Qu H, Dvorak AM (1997). Ultrastructural localization of osteopontin immunoreactivity in phagolysosomes and secretory granules of cells in human intestine. Histochem J 29:801–812.[CrossRef][Medline] [Order article via Infotrieve]
• Rangan GK, Wang Y, Harris DC (2001). Pharmacologic modulators of nitric oxide exacerbate tubulointerstitial inflammation in proteinuric rats. J Am Soc Nephrol 12:1696–1705.[Abstract/Free Full Text]
• Reinholt FP, Hultenby K, Oldberg A, Heinegard D (1990). Osteopontin—a possible anchor of osteoclasts to bone. Proc Natl Acad Sci USA 87:4473–4475.[Abstract/Free Full Text]
• Rittling SR, Matsumoto HN, McKee MD, Nanci A, An XR, Novick KE, et al. (1998). Mice lacking osteopontin show normal development and bone structure but display altered osteoclast formation in vitro. J Bone Miner Res 13:1101–1111.[CrossRef][Medline] [Order article via Infotrieve]
• Roes J, Choi BK, Cazac BB (2003). Redirection of B cell responsiveness by transforming growth factor beta receptor. Proc Natl Acad Sci USA 100:7241–7246. Epub 2003 May 28.[Abstract/Free Full Text]
• Rollo EE, Denhardt DT (1996). Differential effects of osteopontin on the cytotoxic activity of macrophages from young and old mice. Immunology 88:642–647.[CrossRef][Medline] [Order article via Infotrieve]
• Rollo EE, Laskin DL, Denhardt DT (1996). Osteopontin inhibits nitric oxide production and cytotoxicity by activated RAW264.7 macrophages. J Leukoc Biol 60:397–404.[Abstract]
• Scatena M, Almeida M, Chaisson ML, Fausto N, Nicosia RF, Giachelli CM (1998). NF-kappaB mediates alphavbeta3 integrin-induced endothelial cell survival. J Cell Biol 141:1083–1093.[Abstract/Free Full Text]
• Schaller M, Boeld U, Oberbauer S, Hamm G, Hube B, Korting HC (2004). Polymorphonuclear leukocytes (PMNs) induce protective Th1-type cytokine epithelial responses in an in vitro model of oral candidosis. Microbiology 150(Pt 9):2807–2813.[Abstract/Free Full Text]
• Shi HN, Walker A (2004). Bacterial colonization and the development of intestinal defences. Can J Gastroenterol 18:493–500.[Medline] [Order article via Infotrieve]
• Shinohara ML, Lu L, Bu J, Werneck MF, Kobayashi KS, Glimcher LH, et al. (2006). Osteopontin expression is essential for interferon- production by plasmacytoid dendritic cells. Nat Immunol (in press).
• Sibalic V, Fan X, Loffing J, Wuthrich RP (1997). Upregulated renal tubular CD44, hyaluronan, and osteopontin in kdkd mice with interstitial nephritis. Nephrol Dial Transplant 12:1344–1353.[Abstract/Free Full Text]
• Smith LL, Giachelli CM (1998). Structural requirements for alpha 9 beta 1-mediated adhesion and migration to thrombin-cleaved osteopontin. Exp Cell Res 242:351–360.[CrossRef][Medline] [Order article via Infotrieve]
• Sodek J, Ganss B, McKee MD (2000). Osteopontin. Crit Rev Oral Biol Med 11:279–303.[Abstract/Free Full Text]
• Sodek J, Zhu B, Huynh MH, Brown TJ, Ringuette M (2002). Novel functions of the matricellular proteins osteopontin and osteonectin/SPARC. Connect Tissue Res 43:308–319.[Medline] [Order article via Infotrieve]
• Speyer CL, Neff TA, Warner RL, Guo RF, Sarma JV, Riedemann NC, et al. (2003). Regulatory effects of iNOS on acute lung inflammatory responses in mice. Am J Pathol 163:2319–2328.[Abstract/Free Full Text]
• Steele C, Leigh J, Swoboda R, Fidel PL Jr (2000). Growth inhibition of Candida by human oral epithelial cells. J Infect Dis 182:1479–1485. Epub 2000 Oct 09.[CrossRef][Medline] [Order article via Infotrieve]
• Suzuki K, Zhu B, Rittling SR, Denhardt DT, Goldberg HA, McCulloch CA, et al. (2002). Colocalization of intracellular osteopontin with CD44 is associated with migration, cell fusion, and resorption in osteoclasts. J Bone Miner Res 17:1486–1497.[CrossRef][Medline] [Order article via Infotrieve]
• Takahashi F, Takahashi K, Maeda K, Tominaga S, Fukuchi Y (2000). Osteopontin is induced by nitric oxide in RAW 264.7 cells. IUBMB Life 49:217–221.[CrossRef][Medline] [Order article via Infotrieve]
• Tamura A, Shingai M, Aso N, Hazuku T, Nasu M (2003). Osteopontin is released from the heart into the coronary circulation in patients with a previous anterior wall myocardial infarction. Circ J 67:742–744.[CrossRef][Medline] [Order article via Infotrieve]
• Thibault G, Lacombe MJ, Schnapp LM, Lacasse A, Bouzeghrane F, Lapalme G (2001). Upregulation of alpha(8)beta(1)-integrin in cardiac fibroblast by angiotensin II and transforming growth factor-beta1. Am J Physiol Cell Physiol 281:C1457–C1467.[Abstract/Free Full Text]
• Tlaskalova-Hogenova H, Stepankova R, Hudcovic T, Tuckova L, Cukrowska B, Lodinova-Zadnikova R, et al. (2004). Commensal bacteria (normal microflora), mucosal immunity and chronic inflammatory and autoimmune diseases. Immunol Lett 93(2–3):97–108.[CrossRef][Medline] [Order article via Infotrieve]
• Tomasek JJ, Gabbiani G, Hinz B, Chaponnier C, Brown RA (2002). Myofibroblasts and mechano-regulation of connective tissue remodelling. Nat Rev Mol Cell Biol 3:349–363.[CrossRef][Medline] [Order article via Infotrieve]
• Trueblood NA, Xie Z, Communal C, Sam F, Ngoy S, Liaw L, et al. (2001). Exaggerated left ventricular dilation and reduced collagen deposition after myocardial infarction in mice lacking osteopontin. Circ Res 88:1080–1087.[Abstract/Free Full Text]
• Tuck AB, Hota C, Wilson SM, Chambers AF (2003). Osteopontin-induced migration of human mammary epithelial cells involves activation of EGF receptor and multiple signal transduction pathways. Oncogene 22:1198–1205.[CrossRef][Medline] [Order article via Infotrieve]
• Ueno H, Murakami M, Okumura M, Kadosawa T, Uede T, Fujinaga T (2001). Chitosan accelerates the production of osteopontin from polymorphonuclear leukocytes. Biomaterials 22:1667–1673.
• Vaalamo M, Karjalainen-Lindsberg ML, Puolakkainen P, Kere J, Saarialho-Kere U (1998). Distinct expression profiles of stromelysin-2 (MMP-10), collagenase-3 (MMP-13), macrophage metalloelastase (MMP-12), and tissue inhibitor of metalloproteinases-3 (TIMP-3) in intestinal ulcerations. Am J Pathol 152:1005–1014.[Abstract]
• Vogt MH, Lopatinskaya L, Smits M, Polman CH, Nagelkerken L (2003). Elevated osteopontin levels in active relapsing-remitting multiple sclerosis. Ann Neurol 53:819–822.[CrossRef][Medline] [Order article via Infotrieve]
• von Lampe B, Barthel B, Coupland SE, Riecken EO, Rosewicz S (2000). Differential expression of matrix metalloproteinases and their tissue inhibitors in colon mucosa of patients with inflammatory bowel disease. Gut 47:63–73.[Abstract/Free Full Text]
• Wahl SM, Chen W (2003). TGF-beta: how tolerant can it be? Immunol Res 28:167–179.[CrossRef][Medline] [Order article via Infotrieve]
• Wang X, Mosmann T (2001). In vivo priming of CD4 T cells that produce interleukin (IL)-2 but not IL-4 or interferon (IFN)-gamma, and can subsequently differentiate into IL-4- or IFN-gamma-secreting cells. J Exp Med 194:1069–1080.[Abstract/Free Full Text]
• Watford WT, Moriguchi M, Morinobu A, O’Shea JJ (2003). The biology of IL-12: coordinating innate and adaptive immune responses. Cytokine Growth Factor Rev 14:361–368.[CrossRef][Medline] [Order article via Infotrieve]
• Weber GF (2002). Meeting report: the next interleukin? Sci STKE 2002(147):PE37.[Medline] [Order article via Infotrieve]
• Weber GF, Cantor H (1996). The immunology of Eta-1/osteopontin. Cytokine Growth Factor Rev 7:241–248.[CrossRef][Medline] [Order article via Infotrieve]
• Weber GF, Ashkar S, Glimcher MJ, Cantor H (1996). Receptor-ligand interaction between CD44 and osteopontin (Eta-1). Science 271:509–512.[Abstract]
• Weber GF, Zawaideh S, Hikita S, Kumar VA, Cantor H, Ashkar S (2002). Phosphorylation-dependent interaction of osteopontin with its receptors regulates macrophage migration and activation. J Leukoc Biol 72:752–761.[Abstract/Free Full Text]
• Weiss JM, Renkl AC, Maier CS, Kimmig M, Liaw L, Ahrens T, et al. (2001). Osteopontin is involved in the initiation of cutaneous contact hypersensitivity by inducing Langerhans and dendritic cell migration to lymph nodes. J Exp Med 194:1219–1229.[Abstract/Free Full Text]
• Wooten RM, Ma Y, Yoder RA, Brown JP, Weis JH, Zachary JF, et al. (2002). Toll-like receptor 2 is required for innate, but not acquired, host defense to Borrelia burgdorferi. J Immunol 168:348–355.[Abstract/Free Full Text]
• Yamamoto N, Sakai F, Kon S, Morimoto J, Kimura C, Yamazaki H, et al. (2003). Essential role of the cryptic epitope SLAYGLR within osteopontin in a murine model of rheumatoid arthritis. J Clin Invest 112:181–188.[CrossRef][Medline] [Order article via Infotrieve]
• Yumoto K, Ishijima M, Rittling SR, Tsuji K, Tsuchiya Y, Kon S, et al. (2002). Osteopontin deficiency protects joints against destruction in antitype II collagen antibody-induced arthritis in mice. Proc Natl Acad Sci USA 99:4556–4561.[Abstract/Free Full Text]
• Zhu B, Suzuki K, Goldberg HA, Rittling SR, Denhardt DT, McCulloch CA, et al. (2004). Osteopontin modulates CD44-dependent chemotaxis of peritoneal macrophages through G-protein-coupled receptors: evidence of a role for an intracellular form of osteopontin. J Cell Physiol 198:155–167.[CrossRef][Medline] [Order article via Infotrieve]
• Zhu XL, Ganss B, Goldberg HA, Sodek J (2001). Synthesis and processing of bone sialoproteins during de novo bone formation in vitro. Biochem Cell Biol 79:737–746.[CrossRef][Medline] [Order article via Infotrieve]
• Zohar R, Suzuki N, Suzuki K, Arora P, Glogauer M, McCulloch CA, et al. (2000). Intracellular osteopontin is an integral component of the CD44-ERM complex involved in cell migration. J Cell Physiol 184:118–130.[CrossRef][Medline] [Order article via Infotrieve]
• Zohar R, Zhu B, Liu P, Sodek J, McCulloch CA (2004). Increased cell death in osteopontin-deficient cardiac fibroblasts occurs by a caspase 3-independent pathway. Am J Physiol Heart Circ Physiol 287:H1730–H1739.[Abstract/Free Full Text]

Journal of Dental Research, Vol. 85, No. 5, 404-415 (2006)
DOI: 10.1177/154405910608500503


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