Secretion of immunoglobulins and IgM rheumatoid factor by pokeweed mitogen-induced blood lymphocytes: an evaluation by plaque forming cell assays.

The numbers of pokeweed mitogen (PWM)-induced IgM-, IgG- and IgA-secreting cells (SC) in mononuclear cell cultures from patients with seropositive and seronegative rheumatoid arthritis (RA) were reduced compared to those of control persons. Significant numbers of IgM rheumatoid factor (RF)-SC were only found in PWM-induced cultures from patients with seropositive RA (median: 7 IgM RF-SC/10(6) and controls greater than or equal to 50 years (median: 6 IgM RF-SC/10(6). The ratio of IgM RF-SC to total IgM-SC (RF/IgM-SC ratio) was significantly higher in patients with seropositive RA (median: 0.6%) than in controls greater than or equal to 50 years (median: 0.1%). Patients with seropositive RA and RF/IgM-SC ratios above 0.5% had higher Waaler-Rose titers than those with ratios under 0.5%. Our results indicate that secretion of Ig by PWM-induced blood lymphocytes is suppressed in patients with RA compared to controls; in seropositive RA a higher fraction of in vitro activated IgM-SC secrete IgM RF as compared to controls and patients with seronegative RA.