Maciel KF, Neves de Brito LC, Tavares WLF, Moreira G, Nicoli JR, Vieira LQ, Ribeiro Sobrinho AP. Cytokine expression in response to root canal infection in gnotobiotic mice. International Endodontic Journal, 45, 354–362, 2012.
Aim To examine cytokine expression profiles during periapical lesion development in response to synergetic human pathogens in a gnotobiotic mouse model.
Methodology Human strains of Fusobacterium nucleatum and Peptostreptococcus prevotii were inoculated into the root canals of germ-free mice in either mono- or bi-association. Animals were killed 7 and 14 days after infection, and periapical tissues were collected. mRNA expression of the cytokines IFN-γ, TNF-α, Receptor activator of nuclear factor kappa-B ligand (RANKL), IL-10, IL-4 and transforming growth factor β (TGF-β) was assessed using real-time PCR. Levene’s test was used to assess the equality of variance of the data, whereas a t-test for independent samples was used to evaluate the significance of the differences between groups (P < 0.05).
Results The mRNA expression of IFN-γ and TNF-α was up-regulated by F. nucleatum during the acute (day 7) and chronic phase (day 14) of periapical lesion development. However, in bi-infection the expression of IFN-γ and TNF-α were effectively absent at both time-points. RANKL mRNA expression was down-regulated during dual infection at the chronic phase. As IL-4 expression was similar at both time-points, IL-4 does not appear to be involved in the periapical response to these bacterial strains. IL-10 was up-regulated during the chronic phase by mono-infection with either F. nucleatum or P. prevotii. Dual infection increased TGF-β mRNA expression on day 7, which paralleled the decrease in IFN-γ and TNF-α mRNA levels at the same time-point. F. nucleatum increased TGF-β mRNA expression during the chronic phase.
Conclusion Cytokine profiles depend on the nature of the bacterial challenge. Both TGF-β and IL-10 appeared to be regulating the proinflammatory cytokine responses at both time-points of the periapical immune response.