We demonstrated that treatment of mice with CIA with 20S(OH)D3 reduces the severity of clinical arthritis accompanied by reduction in joint destruction, in serum anti-CII antibodies, in lymphoid organ CD4+ T and CD19+ B cells, and production by cultured draining lymph node cells of TH1, TH17, and inflammatory cytokines and chemokines. The gene discussed is CD19; the disease is Arthritis.