Enhancement of Clq binding activity by IgM rheumatoid factor.
Clq binding activity (ClqBA) averaged 18.1 +/- 14.5% (1 SD) in 28 rheumatoid arthritis (RA) sera (normal sera = 3.9 +/- 0.4%). Further analysis indicated that rheumatoid factor (RF) positive [RA (+)] sera averaged 30.4% ClqBA, significantly greater than the 3.9% ClqBA in RA RF negative [RA(-)] sera (p less than 0.01). In the RA(+) sera, RF titer correlated with ClqBA (r = +0.73). Addition of IgM RF to sera of normal, SLE, and RA(-) patients, as well as to aggregated IgG and reduced and alkylated aggregated IgG, resulted in significant increases in ClqBA, up to 14% in the latter group (p less than 0.01). Control IgM added to these same systems had no effect on ClqBA. IgM RF only slightly increased Clq binding of monomeric IgG.
D000936:Antigen-Antibody Complex / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D003166:Complement Activating Enzymes / Q000378:metabolism*; D015922:Complement C1q; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D007075:Immunoglobulin M / Q000378:metabolism*; D066298:In Vitro Techniques; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D012217:Rheumatoid Factor / Q000378:metabolism*
D000936:Antigen-Antibody Complex; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D015922:Complement C1q; D012217:Rheumatoid Factor; D003166:Complement Activating Enzymes