T helper 17 (Th17) cells are a unique lineage of proinflammatory effector and memory T helper cells that play a prominent role in the pathogenesis of systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), psoriasis, multiple sclerosis (MS), and inflammatory bowel disease (IBD) by activation of pathogenic CD4+ and CD8+ T cells [132,135,136,137]. The gene discussed is CD4; the disease is rheumatoid arthritis.