Extracts of periodontopathic microorganisms lack functional superantigenic activity for murine T cells

Products of periodontopathic bacteria exert immunomodulatory effects on various lymphoid cell populations, some of which have been implicated in the pathogenesis of periodontitis. It has recently been suggested that some of these bacterial products may possess superantigenic (SAg) activity. SAg bind simultaneously to the V beta chain of T cell receptors and to class II major histocompatibility complex molecules, thereby activating as many as 35% of T cells to proliferate and produce cytokines. In order to examine this question, the proliferation of splenic and thymic T cells from immunologically naive, 3-6-wk-old Balb/c (H-2d), C57BL/6 (H-2b) and C3H/HeJ (H-2k) mice was assessed in response to sonic extracts of periodontopathogens. Laboratory and/or reference strains of a.o. Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia and Prevotella nigrescens were used as stimulants. Staphylococcal enterotoxin B (SEB), a known superantigen, was utilized as a positive control. Unfractionated spleen cells responded to several of the tested preparations of the different bacteria, as well as to SEB, Con A and Escherichia coli LPS. Thymocytes responded to Con A and SEB, but not to LPS or to any sonic extract. Spleen cells depleted of B cells by panning responded to SEB and Con A, but not to LPS and showed a reduced response to sonicates. The residual response of B cell-depleted spleen cells was reduced essentially to background by treatment with anti-Thy 1.2 + C'. Similar results were obtained in the presence of 5% added mitomycin-treated antigen presenting cells, indicating that these cells were not limiting. These results demonstrate that extracts of periodontopathic bacteria do not stimulate murine T cells in a manner consistent with superantigenic activation.