Porphyromonas gingivalis stimulates IL-18 secretion in human monocytic THP-1 cells

Porphyromonas gingivalis is a major pathogen implicated in chronic periodontitis. We examined whether P. gingivalis affected the secretion of the pro-inflammatory cytokine interleukin-18 (IL-18) in macrophage-like THP-1 cells and in monocytic THP-1 cells in suspension. Live P. gingivalis-induced significant IL-18 secretion. Heat-inactivation of P. gingivalis greatly reduced the IL-18 stimulation; the IL-18 levels were similar to that observed with P. gingivalis LPS alone. Live P. gingivalis caused a cytotoxic effect that was reduced greatly by heat-inactivation. Our observations indicate that P. gingivalis specifically stimulates the production and release of the active form of IL-18, which may contribute to the progression of periodontitis.