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Extracellular 37-kDa Antigenic Protein from Actinobacillus actinomycetemcomitans Induces TNF-, IL-1β, and IL-6 in Murine Macrophages

Department of Periodontology, Nagasaki University School of Dentistry, 1-7-1 Sakamoto Nagasaki 852, Japan

M. Tani

Department of Periodontology, Nagasaki University School of Dentistry, 1-7-1 Sakamoto Nagasaki 852, Japan

I. Kato

Department of Periodontology, Nagasaki University School of Dentistry, 1-7-1 Sakamoto Nagasaki 852, Japan

The extracellular antigens of Actinobacillus actinomycetemcomitans Y4 (serotype b) contain a 37-kDa protein which is a major target for IgGs from patients suffering from severe alveolar bone loss. Since the 37-kDa protein has not been studied sufficiently, our investigation focused on its characteristics, e.g., its localization, specificity, and whether it directly stimulates macrophages to produce cytokines. The 37-kDa protein was purified from the culture supernatant of the Y4 strain by means of chromatofocusing and gel filtration. The 37-kDa protein is a unique glycoprotein which forms immune complexes with monoclonal antibodies against rhamnose-fucose polysaccharide. Patients with A. actinomycetemcomitans-associated periodontitis had higher antibody titers to the purified 37-kDa protein than healthy subjects (p < 0.001). Anti-37-kDa protein antibodies recognized a 37-kDa band in the cytosolic, ribosomal, and total membrane fractions from Y4 cells. Extracellular substances from other strains of A. actinomycetemcomitans (serotypes a and c) also reacted in the Western blots, but Haemophilus spp. or several periodontopathic bacteria did not. These results suggested that the 37-kDa protein is a cytosolic protein that is passed through the cell membrane, and its protein portion is specific for A. actinomycetemcomitans but common to serotypes. This protein induced IL-1β, IL-6, and TNF-a release from murine macrophages. The IL-6-inducing activity of the 37-kDa protein was higher than that of LPS. These findings suggested that the 37-kDa protein which is released from live cells plays a role in A. actinomycetemcomitans- associated periodontitis, as antigen inducing the release of inflammatory cytokines which are associated with alveolar bone loss.

Key Words: A. actinomycetemcomitans • extracellular 37-kDa protein • murine macrophage • inflammatory cytokine • LPS.

Journal of Dental Research, Vol. 76, No. 9, 1538-1547 (1997)
DOI: 10.1177/00220345970760090501


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