Development of IL-17-mediated Delayed-Type Hypersensitivity Is Not Affected by Down-Regulation of IL-25 Expression

Background: IL-25, which is a member of the IL-17 family, induces Th2 cell differentiation and Th2 cytokine production, contributing to induction of Th2-type immune responses and diseases, as a result of which it suppresses Th1- and Th17-type immune responses. Methods: To elucidate the role of IL-25 in the pathogenesis of IL-17-mediated delayed-type hypersensitivity (DTH), IL-25-deficient mice were sensitized with methylated BSA (mBSA), and then a DTH reaction was induced by mBSA challenge. mBSA-specific T-cell induction was assessed on the basis of cell proliferation and cytokine production. The DTH reaction was evaluated on the basis of tissue swelling, histology and inflammatory mediator expression. Results: IL-25 expression was markedly reduced in local DTH lesions. However, mBSA-specific Th1, Th2 and Th17 cell induction, and the mBSA-induced DTH reaction were comparable in IL-25-deficient and wild-type mice. Conclusions: IL-25 is not essential for differentiation of Th1, Th2 and Th17 cells in the sensitization phase or induction of local inflammation in the elicitation phase of the mBSA-induced DTH reaction.