By stimulating IL-6-driven arthritogenic Th17 cells, genetically modified T cells in mice cause rheumatoid arthritis-like arthritis. Arthritis is inhibited by low levels of IL-17 or IL-6, and worsened by low levels of interferon-gamma. The results recommend therapies for autoimmune disorders, particularly rheumatoid arthritis. The gene discussed is IL17A; the disease is rheumatoid arthritis.