The stimulation of IgM rheumatoid factor from human B lymphocytes by rheumatoid arthritis complement-activating immune complexes.

Immune complexes from rheumatoid arthritis (RA IC) and Hodgkin's disease (HD IC) sera were separated on an anti-C3g affinity column and their ability to stimulate the production of IgM and IgM RF by normal and RA B lymphocytes tested in a culture system in vitro. RA IC stimulated IgM production of which up to 91.3% had IgM RF activity. HD IC were incapable of stimulating the production of IgM and IgM RF. The stimulation of IgM and IgM RF production by RA IC required de novo protein synthesis. Both RA IC and HD IC were capable of significantly inhibiting (from 47.6 to 72.0%) pokeweed mitogen (PWM)-induced and goat F(ab)2 antihuman mu-induced B lymphocyte proliferation. Thus it is proposed that IC present in human pathological sera may regulate immunoglobulin production by an effect on B lymphocyte proliferation while some may, in addition, be capable of inducing IgM RF production from such cells.