The IL-17 pathway as a major therapeutic target in autoimmune diseases.

Th17 cells are a subset of T helper cells that have been recently found to play important functions in host defense and the pathogenesis of various human autoimmune and inflammatory diseases. Th17 cells produce IL-17A, IL-17F, IL-22, and IL-21, of which IL-17A and IL-17F mediate many of the downstream pathologic functions of these cells. IL-17A and IL-17F signal through IL-17RA and IL-17RC heterodimeric receptors that are mainly expressed on tissue epithelial cells and fibroblasts. While IL-17A and IL-17F are important for host defense against many extracellular pathogens, they can also cause excessive tissue damage and exacerbate proinflammatory responses during autoimmunity. The IL-17 pathway, therefore, is a primary therapeutic target downstream of Th17 cells.