IL17A and autoimmune disease: IL-17A, commonly known as IL-17, and its binding receptor IL-17RA were discovered in the middle 1990s,152,153 which was found upregulated in human inflammatory and autoimmune disease.154,155 The source of IL-17 could not be determined in any cluster of lymphocytes known at the time until the discovery of IL-17-secreting Th17 cells ten years later.