Gingipains are the important virulence factors of Porphyromonas gingivalis downregulating B10 cells

Porphyromonas gingivalis is a keystone pathogen in periodontitis. Our previous study indicated that periodontitis induced by P. gingivalis increased the percentage of CD19+ B cells but decreased the ratio of IL-10-producing regulatory B cells (B10) in collagen-induced arthritis (CIA) mice. It is still unclear which virulence factors of P. gingivalis are involved in these processes. Here, we compared the effects of different components of P. gingivalis on the biogenesis of B10 cells and found that the decreased proportion of B10 cells mainly resulted from the undenatured proteins other than the DNA, RNA, or lipopolysaccharides of P. gingivalis. As gingipains are enzymes and virulence factors that play a vital role in the progression in periodontitis through affecting the innate and adaptive immune system, we then compared the influence of the wild-type (WT) strain of P. gingivalis (ATCC 33277) and its isogenic gingipain-null mutant (∆K∆RAB) on the differentiation of splenic B cells into B10 cells. Interestingly, compared to WT strain, ∆K∆RAB treatment increased the frequency of B10 cells as well as the expression of IL-6 in B cells. Furthermore, the acute peritonitis, an ideal model for the quick evaluation of immune effects of agents, induced by ∆K∆RAB, showed the higher IL-6 production and proportion of B10 cells compared with WT. Finally, we performed transcriptomic analysis to better understand the effects and possible mechanisms of gingipains on B cells. Compared with WT, ∆K∆RAB upregulated the PI3K-Akt pathway of B cells, which is important for IL-10 production and B10 cell biogenesis, and more activated Jak-STAT pathway, which is a classical signaling pathway mediated by IL-6. Cumulatively, this study preliminarily revealed that gingipains of P. gingivalis are vital virulence factors downregulating B10 cells and altering immune responses.