Interferon-gamma deficiency attenuates local P. gingivalis-induced Inflammation

Infection with the periodontal pathogen Porphyromonas gingivalis causes a strong local inflammatory reaction. Using IFNγ-deficient mice, we tested the hypothesis that the absence of IFNγ would result in a reduction of the local pro-inflammatory response to P. gingivalis. Cytokine secretion by macrophages from IFNγ^-/- animals was significantly attenuated. Addition of IFNγ restored cytokine secretion. In vivo injection of P. gingivalis into subcutaneous chambers increased the intra-chamber leukocyte counts and TNFα and IL-1β levels. This increase was significantly lower in the IFNγ^-/- mice. Local reconstitution of IFNγ^-/- mice at the site of inflammation with the IFNγ gene increased the levels of TNFα and decreased the IL-10 levels. Anti-P. gingivalis IgG1 levels, a marker of Th2 response, were higher in immunized IFNγ^-/- than in IFNγ^+/+ mice. The results suggest that lack of IFNγ reduced the amplitude of the local pro-inflammatory response without decreasing the humoral protective response. The higher IgG1/IgG2a ratio observed supports the possibility of a Th2-dominant response in IFNγ-deficient animals.