Enhanced in vitro synthesis of IgM rheumatoid factor in rheumatoid arthritis

Peripheral blood mononuclear leukocytes (MNL) from 42 patients with classic/definite seropositive rheumatoid arthritis (RA) and 24 healthy adult controls were tested for their capacity to produce IgM rheumatoid factor (RF) in vitro in the presence and absence of pokeweed mitogen (PWM). In no instance was spontaneous elaboration of IgM RF from control MNL observed. In contrast, MNL from 16 of the 42 RA patients spontaneously synthesized IgM RF (22 +/- 43 ng/culture) which constituted a substantial fraction of the total IgM in these culture fluids (48 +/- 26%). Pokeweed mitogen induced detectable quantities of IgM RF in MNL culture supernatants from 10 of 24 controls (12 +/- 11 ng/culture) and 33 of 42 RA patients (60 +/- 82 ng/culture, P = 0.008). IgM RF constituted a significantly higher proportion of the total IgM in RA MNL supernatants than in control supernatants (11 +/- 11% versus 1.01 +/- 1.03%; P = 0.013). IgM RF production (spontaneous and PWM-induced) was dependent upon de novo protein synthesis. The results indicate that B cells programmed to produce IgM RF are present in both normal and RA B cell repertoires, but are preferentially expressed in RA.