Apoptosis in Porphyromonas gingivalis-specific T-cell lines

Fluorescence-activated cell sorter analysis and transmission electron micro scopy were used to determine the presence of apoptotic cells in Porphyromon as gingivalis-specific T-cell lines established from the peripheral blood o f 10 P. gingivalis-infected individuals. P. gingivalis outer membrane antig ens were presented to the T cells by autologous Epstein-Barr virus-transfor med B cells for 6, 24, 48 and 72 h. Transmission electron microscopy demons trated the presence of typical apoptotic cells in all cultures. Annexin V-p ositive cells were present at low concentrations at all 4 four periods. A m ean of approximately 2-3% of the CD4 cells and 1-3.5% of the CD8 cells were annexin V-positive, with an increase to around 5.5% positive CD4 cells at 6 h in wells containing P. gingivalis compared with cultures not containing antigen. This difference was not, however, significant at the 0.05 level ( P=0.073). The mean (+/-standard error) CD4:CD8 ratios of the T-cell lines w hen first established using peripheral blood mononuclear cells as antigen-p resenting cells was significantly higher (5.2+/-1.1) than when transformed B cells were used as antigen-presenting cell (1.2+/-0.5). While this study has shown apoptosis occurring in the T-cell lines, it has not shown definit ively that the reversion in the CD4:CD8 ratio in the P. gingivalis-specific T cells following antigen presentation by autologous Epstein-Barr virus-tr ansformed B cells is due to apoptosis of a CD4 population. Alternatively, t he reversion in the CD4:CD8 ratio could be due to a selective proliferation of the CD8 population which, in turn, could be relevant to the immunopatho logy of periodontal disease induced by P. gingivalis.