Antigen-speciˆc CD4 + helper T cell (Th cell) is a major player for acquired-immunity. Th cell distribute in the peripheral tissues after educations and selections in the thymus. By stimulation from antigen presenting cell (APC), Th cell diŠerentiate into at least three types of eŠector Th cells by the cytokine environments and the kinds of co-stimulatory molecules on APC. One is Th1 cell which produces IFN g mainly, and another is Th2 cell which produces IL 4, 5 and 13 mainly, andˆnally

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... tly deˆned Th17 cell which produces IL 17 mainly, and these cells are charged with the a role for"cellular","hormoral" and"in‰ammatory" immunity respectively. IL 12, STAT4 and T bet signals are important for Th1 diŠerentiation, and IL 4, STAT6 andGATA3 signals are important for Th2 diŠerentiation, and IL 1b, TGF b, IL 6, IL 23, STAT3, RORgt signals are important for Th17 diŠerentiation. This newly deˆned Th17 cell clearly makes a big progress for understanding the pathophysiology of many in‰ammatory conditions. In the near future, many biologics or compounds that regulate the production or function of IL 17 will be produced aggressively.