Interleukin (IL)-17 acts as a potent inflammatory cytokine, and IL-17-producing cells (Th17 cells) have received much attention. However, the involvement of commensal and/or probiotic bacteria in IL-17 production has not been evaluated. In this study, we examined the suppressive effects of five bacteria species on IL-17 production in vitro and ex vivo. Among the five species studied, Bifidobacterium infantis inhibited IL-17 production but enhanced IL-27 production most potently in TGF-β plus IL-6-stimulated murine splenocytes. B. infantis also inhibited IL-17 and eotaxin production from a dextran sodium sulfate-treated colon organ culture. The induction of IL-10 by B. infantis was observed both in the splenocytes and in the colon culture and was assumed, to a certain extent, to be important for suppressing IL-17 production. These findings suggest a novel immunomodulatory function of commensal bifidobacteria and further imply that these bacteria may be useful in the treatment of Th17-mediated diseases.

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