Even though we did not observe an increase in circulating GM-CSF+ lymphocytes in RA, the efficacy of the anti-GM-CSF antibody in this disease may be predominantly due to the local effects of GM-CSF in synovial tissue, where increased numbers of cells expressing the GM-CSF receptor have been described in both RA and psoriatic arthritis45. The gene discussed is CSF2; the disease is rheumatoid arthritis.