Complement activating properties of monoreactive and polyreactive IgM rheumatoid factors.

OBJECTIVES To estimate the complement activating properties of monoclonal, monoreactive, and polyreactive IgM rheumatoid factors derived from Epstein-Barr virus transformed B cells isolated from peripheral blood and synovial tissue of patients with rheumatoid arthritis (RA). METHODS An enzyme linked immunosorbent assay (ELISA) was used to measure the activation of the classical pathway of complement by monoclonal IgM rheumatoid factor. Monoclonal IgM rheumatoid factor was bound to IgG Fc adsorbed onto microtitre plates and then reacted with diluted normal human serum as a source of complement. The activation and binding of C4 were measured with F(ab')2 antibody to human C4. The complement activating property of IgM rheumatoid factor bound to IgG Fc was tentatively expressed as the ratio of the amount of bound C4 to the amount of bound IgM rheumatoid factor. RESULTS The complement activating property of monoreactive IgM rheumatoid factor was shown to be about three times higher than that of polyreactive IgM rheumatoid factor. CONCLUSIONS Monoreactive IgM rheumatoid factor with the higher complement activating property would result in a greater degree of complement dependent inflammation and might have a more important pathogenic role in RA than polyreactive IgM rheumatoid factor.