DIFFERENT RESPONSES IN B-CELLS INDUCED BY PORPHYROMONAS-GINGIVALIS AND FUSOBACTERIUM-NUCLEATUM

A phenotypic study had shown that gingival B cells respond differently to two periodontopathic bacteria, Porphyromonas gingivalis and Fusobacterium nucleatum. Further investigation now shows a reduction in the percentage of Ki-67+ T cells in cultures of gingival and peripheral blood mononuclear cells stimulated with P. gingivalis for 3 and 6 days, respectively, but no suppression of Ki-67 expression in B cells in response to either P. gingivalis or F. nucleatum. Depletion studies of cultures of peripheral blood mononuclear cells showed that in the absence of CD4 cells, the percentage of CD19+ and CD20+ B cells stimulated with P. gingivalis increased after 6 days whereas depletion of CD8 cells resulted in a rise in the percentage of F. nucleatum - and P. gingivalis-stimulated B cells, although this was not significant in the case of P. gingivalis. Specific antibody to P. gingivalis and F. nucleatum was found in culture supernatants of gingival but not of peripheral blood mononuclear cells, indicating a possible higher frequency of antigen-specific B cells in periodontal lesions. IgG was the predominant isotype in both gingival and control peripheral blood cultures, followed closely by IgA in gingival cultures. F. nucleatum stimulated higher levels of Ig in cultures of peripheral blood mononuclear cells than P. gingivalis or cells cultured in medium only, whereas in gingival cell cultures, stimulation by P. gingivalis appeared to result in higher levels of IgG. Also Ig was present at day 3 in gingival cultures, whereas in the blood cell cultures, Ig was only detected at day 6, further suggesting a degree of activation of gingival B cells. These results confirm that P. gingivalis and F. nucleatum induce different responses in B cells extracted from either periodontal tissues or normal peripheral blood and may also suggest different T-cell control mechanisms.