CSF1R and rheumatoid arthritis: CSF1 and its receptor c-fms are more elevated in in the synovium and synovial fluid of patients with rheumatoid arthritis, compared to those with osteoarthritis.36,37 An anti-CSF1 antibody, an antibody to c-fms, and the c-fms inhibitors Ki20227 and GW2580, have all been shown to significantly reduce the severity of joint disease in a murine model of inflammatory arthritis.36–40