Interleukin 17 (IL-17), also referred to as IL-17A, is a member of a family of cytokines that includes IL-17B, -17C, -17D, -17E and -17F. IL-17 function is essential to a subset of CD4+ T-Cells called T helper 17 (Th17) cells. IL-17A is a pro-inflammatory cytokine primarily secreted by T lymphocytes. It promotes expansion and recruitment of innate immune cells such as neutrophils and stimulates production of beta-defensins and other anti-microbial peptides.
IL-17 binds to and signals through a transmembrane, heterotrimeric receptor complex that consists of IL-17 receptor A (IL-17RA), IL-17 receptor B (IL-17RB) and IL-17 receptor C (IL-17RC). IL-17A activates NF-kappaB and MAPK pathways via adapter molecules TRAF6 and ActI. Other signaling pathways like the Ras/ERK and the JAK/PI3K/AKT are also activated leading to the induction of pro-inflammatory cytokines, chemokines, matrix metalloproteinases and anti-microbial peptides. Thus, IL-17 is a unique cytokine that plays a central role in integrating adaptive and innate immune responses.