IgM rheumatoid factor plaque-forming cells in juvenile rheumatoid arthritis.

Using a direct, plaque-forming cell (PFC) assay with sensitized sheep erythrocytes, lymphocytes that secrete IgM rheumatoid factors (RF) have been detected in the peripheral blood of patients with juvenile rheumatoid arthritis. Of 15 juvenile rheumatoid arthritis patients tested, 8 were seropositive and 7 were seronegative, but 6 of the seronegative patients had hidden 19S IgM-RF. Ten patients (5 seropositive and 5 with hidden 19S IgM-RF) demonstrated RF-PFC in their peripheral blood (range 15 to greater than 200 RF-PFC/10(6) mononuclear cells). Of 11 patients who had active disease, 10 had RF-PFC, and the 4 patients who had inactive disease had no PFC in their peripheral blood. HLA typing of all 15 patients revealed no correlation between the presence of RF-PFC and HLA type.