The immune modulation of B-cell responses by Porphyromonas gingivalis and interleukin-10

Background: Polyclonal B-cell activation induced by periodontopathic bacter ia has been cited as being important for elevated numbers of B cells, but t he role of bacteria in the pathogenesis of periodontal disease remains unkn own. In this study, we used an in vitro model to investigate the activation of immune cells by the periodontopathic bacterium Porphyromonas gingivalis in healthy subjects. Methods: Peripheral blood mononuclear cells (PBMC) or purified subsets of l ymphocytes were stimulated with sonicated extracts of P. gingivalis for 24 hours. Cells were harvested and monitored for expression of CD69 by flow cy tometry. Cytokine production (IL-10, IL-12, and IL-15) in gingivalis-stimul ated PBMC cultures was measured by ELISA. To identify IL-10 producer cells, a cell depletion experiment was used and confirmed by the ability of the p urified cell population to produce IL-10. To evaluate the effect of P. ging ivalis and IL-10, the proliferative response of purified B cells was assess ed by [H-3] thymidine uptake. Results: PBMC cultured with P. gingivalis led to a large number of activate d B and natural killer (NK) cells as monitored by CD69 expression. When pos itively sorted cells were used, the bacterium itself could directly activat e only B cells but not NK cells, alpha beta, and gamma delta T cells. Measu rement of B-cell regulatory cytokine production in P. gingivalis-stimulated PBMC cultures revealed a large amount of IL-10 but no detectable IL-12 or IL-15; the major producing cells were monocytes, not B cells or ap T cells. When IL-10 was added to B cells in the presence of bacteria, significantly increased B-cell proliferative responses were observed. Conclusions: These results suggest that P. gingivalis, both directly and in directly via macrophage IL-10, may play an important role in polyclonal B-c ell activation associated with periodontal disease.