Mononuclear cells from rheumatoid arthritis patients exhibit a depressed IgM response to sheep erythrocyte stimulation in vitro.

Human peripheral blood mononuclear cells when cultured for the short term (11 days) produce an optimal IgM plaque-forming cell (PFC) response to sheep erythrocytes, which is dependent on macrophages and T suppressor and helper lymphocytes. With this system we have investigated the PFC response of individuals with rheumatoid arthritis and compared this to the response of normal sex- and age-matched controls and of patients with osteoarthritis. The response of rheumatoid arthritis patients was significantly lower than that of subjects in the other two categories.