Immunologic effects of cyclophosphamide treatment in rheumatoid arthritis

Nine patients with advanced, active rheumatoid arthritis were treated from 4 to 15 months with cyclophosphamide. Eight of the 9 patients had a good to excellent clinical response. Rheumatoid factor titer, serum immunoglobulins and the in vitro lymphocyte response to phytohemagglutinin, pokeweed mitogen and specific antigens decreased with treatment. No direct correlation could be made between the degree of clinical response and the degree of depression of any of the immunologic parameters. The cyclophosphamide-induced suppression of the in vitro lymphocyte response does not appear to be due to a serum factor.