Secretion of IL-17, IL-21, and IL-22 by TH17 cells correlates with the pathogenesis of several autoimmune (rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, and psoriasis) and inflammatory diseases (inflammatory bowel disease and allergy and asthma) (83–89). Here, IL21 is linked to systemic lupus erythematosus.