IL-17A is a cystine-linked homodimeric pro-inflammatory cytokine produced by Th17 cells, a distinct CD4+ T cell lineage. IL-17A stimulates the production of the pro-inflammatory cytokines IL-1?, TNF-?, and IL-6. IL-17A also induces production of the neutrophil chemoattractants IL-8, CXCL1, and CXCL6 thereby bridging adaptive and innate immunity. IL-17A is intimately involved in mucosal immunity against bacterial infections and has a putative role in some autoimmune disorders. IL-17A effects appear to be exerted primarily through binding to the IL-17RA. IL-17A binding induces production of cytokines, chemokines and other proteins through activation of the Erk1/2 MAP kinase, PI3K/Akt, p38, and NF-?B pathways. Phosphorylation of some Jaks and Stats has been observed.