Both rheumatoid arthritis and animal models ofautoimmune arthritis are characterized by hyper-activation of synovial cells and hyperplasia of the synovialmembrane. The activated synovial cells produceinflammatory cytokines and degradative enzymes whichlead to destruction of cartilage and bones. Effectivetreatment of arthritis may require elimination of most orall activated synovial cells. The death factor Fas/Apo-1 Both rheumatoid arthritis and animal models of autoimmune arthritis are characterized by hyper-activation of synovial cells and hyperplasia of the synovial membrane. The activated synovial cells produceinflammatory cytokines and degradative enzymes whichlead to destruction of cartilage and bones. Effective treatment of arthritis may require elimination of most orall activated synovial cells. The death factor Fas / Apo-1