Abstract: IL-17 is the cytokine secreted by the subgroup of CD4+ T cells named Th17. The differentiation, proliferation and cytokine secretion of Th17 are regulated by TGF-β, IL-6, IL-15 and IL-23. IL-17 modulates the production and secretion of proinflammative factors, CXCs, affecting the transfer of neutrophil, the activation and the absorption of bone. It suggests that IL-17 also plays an important role on the development of autoimmune diseases.