Th17 cells synthesize IL-17A, IL-17F, IL-21, and so forth and have been demonstrated in autoimmune disease such as Sjögren's syndrome, multiple sclerosis, psoriasis, autoimmune uveitis, juvenile diabetes, rheumatoid arthritis, and Crohn's disease [15, 16, 20, 33, 34]. The gene discussed is IL21; the disease is psoriasis.