Porphyromonas gingivalis gingipains selectively reduce CD14 expression, leading to macrophage hyporesponsiveness to bacterial infection

Cysteine proteases (gingipains) from Porphyromonas gingivalis are key virulence factors in chronic periodontitis. Innate immune receptors CD14, TLR2 and TLR4 are important in P. gingivalis recognition. We examined the ability of gingipains to cleave CD14, TLR2 and TLR4, and the consequences for the cellular response to bacterial challenge. Murine macrophages were exposed to Arg-(RgpA & RgpB) and Lys-(Kgp) gingipains, and residual expression of TLR2, TLR4 and CD14 was determined by flow cytometry. The cellular response to live bacteria following exposure to purified gingipains was evaluated by TNFα production and bacterial phagocytosis. RgpA and Kgp cleaved CD14, while TLR2 and TLR4 levels were unaffected. RgpA and Kgp decreased CD14 detection in a concentration (P=0.0000002) and time (P=0.03) dependent-manner, whereas RgpB had no significant effect. Reduction of CD14-expression was more efficient with Lys-gingipain than with Arg-gingipain. Reduced CD14 surface level correlated with decreased TNFα secretion and bacterial phagocytosis following challenge with live P. gingivalis, but the response to heat-killed bacteria was unaffected. Therefore, gingipains cleave the TLR co-receptor CD14 but do not affect expression of the bacterial sensing TLRs. Proteolysis of CD14 is dependent on the gingipain hemagglutinin/adhesion-site, and results in macrophage hypo-responsiveness to bacterial challenge. Further studies are needed to determine if reduced CD14 expression is linked to periodontitis induced by P. gingivalis