Cytokines induced by mixed infection with periodontal pathogenic bacteria

Objectives: Recently it is reported that periodontopathogens are related to systemic diseases such as arteriosclerosis, preterm birth and respiratory infection. Our preliminary data demonstrated that mixed infection with Porphyromonas gingivalis ATCC 33277 and Tannerella forsythia ATCC 43037 caused severe inflammatory responses in the lungs of mice but mono-infection did not. On the other hand, it has been reported that mixed infection with P. gingivalis and Treponema denticola in mice induces experimental pneumonia and significantly increases IL-1β and TNF-α production at 24 h after inoculation. In this study, we investigated that each and mixed bacteria induced pro-inflammatory cytokines production by J774.1, mouse macrophage-like cell line, which play a major role in inflammation.

Methods: J774.1 cells were incubated with or without the bacteria for 24 h in 96-well flat-bottomed plates. The culture supernatants were analyzed by ELISA for secreted mouse IL-6, MCP-1, TNF-α, IL-1β and IL-23, and results were determined using a standard curve prepared for each assay.

Results: Mixed infection with P. gingivalis and T. forsythia or T. denticola ATCC35405 at concentrations of 10⁵ CFU/ml caused synergistic IL-6 production but not MCP-1. The production of IL-1β and TNF-α, which are known to enhance IL-6 production, was induced by each bacterium but the synergistic production of both cytokines by the mixed infection did not occur. This trend was also shown in the production of IL-23.

Conclusion: These data suggested that P. gingivalis and T. forsythia or T. denticola induce synergistic IL-6 protein production.