Background: Chronic periodontitis is caused by mixed bacterial infection. Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola are frequently detected in deep periodontal pockets. We demonstrate that these bacteria induce proinflammatory cytokine production by the mouse macrophage-like cell line J774.1.
Materials and methods: J774.1 cells were incubated with and without bacteria for 24h in 96-well flat-bottomed plates. The culture supernatants were analyzed by enzyme-linked immunosorbent assay for secreted mouse interleukin (IL)-6, monocyte chemoattractant protein-1, IL-23, IL-1 beta and tumor necrosis factor-alpha. The cytokine concentrations were determined using a standard curve prepared for each assay.
Results: Mixed infection with P. gingivalis and either T. forsythia or T. denticola at 10(5)CFU/ml acted synergistically to increase IL-6 production, but not monocyte chemoattractant protein-1, IL-23, IL-1 beta or tumor necrosis factor-alpha production. Gingipain inhibitors KYT-1 and KYT-36 inhibited IL-6 production by J774.1 cells incubated with 10(5)CFU/ml of mixed bacteria.
Conclusion: These results suggest that P. gingivalis with either T. forsythia or T. denticola directly induces synergistic IL-6 protein production and that gingipains play a role in this synergistic effect.