IL17A and infection: It has recently been learned that, in a new helper T-cell population having characteristics different from TH1 and TH2, IL-23, which is structurally and functionally similar to IL-12, is deeply involved in promotion of differentiation into Th-17 cells that specifically produce IL-17 without producing IFN-γ, IL-4, or IL-13 and also in induction of inflammation and some immunity to infections [14].