Gingipains in the culture supernatant of Porphyromonas gingivalis cleave CD4 and CD8 on human T cells.

Porphyromonas gingivalis has been shown to attack host defense systems through proteolytic cleavage of a wide variety of members of the systems. In this study, we examined the ability of P. gingivalis culture supernatant to alter the expression of human T cell surface proteins. As judged by flow cytometric analysis, detection of CD4 expression was completely eliminated by the supernatant, but CD8 was less sensitive. When the culture supernatant was added with reducing agents, proteolytic activity was enhanced, resulting in the cleavage of CD8. Mitogenic response of T cells to phytohemagglutinin or concanavalin A was decreased by the treatment of the cells with the culture supernatant of P. gingivalis. The three forms of gingipains (high molecular mass arginine-specific gingipain, arginine-specific gingipain 2 and lysine-specific gingipain) purified from the culture supernatant of P. gingivalis actively cleaved CD4 and CD8 on human T cells, indicating that proteolytic activity of the culture supernatant was due to gingipains. These results suggest that cysteine proteinases like gingipains released from P. gingivalis cleave T cell surface proteins and impede T cell function.