Interleukin-17A (IL-17A), also known as CTLA-8, is a member of the IL-17 family of proteins. IL-17A is a proinflammatory cytokine that is secreted by activated CD4+ and CD8+ T lymphocytes. IL-17A acts through its receptor, IL-17R, to promote increased cytokine and chemokine secretion. In turn, the cytokines and chemokines mediate the immunoregulatory function of IL-17A by promoting the proliferation, maturation, and chemoattraction of neutrophils to inflammatory sites. Elevated levels of IL-17A are associated with rheumatoid arthritis, airway inflammation, allograft rejection, inflammatory bowel disease, psoriasis, cancer, and multiple sclerosis. Human, mouse, and rat IL-17A show activity on mouse cells.