title: Metabolism of C4 and factor B in rheumatoid arthritis. Relation to rheumatoid factor.
abstract: Metabolic turnover determined by radioiodide labeled C4 and Factor B was studied in 18 patients with rheumatoid arthritis (RA) and 19 normal control subjects as a means of estimating the relative ratio of consumption of components in the classical and alternative pathways of complement activation. Predominance of fractional catabolic rate (FCR) of C4 over Factor B was demonstrated with differentially labeled C4 and Factor B. The hypercatabolism occurred in the extravascular space. C4 FCR correlated significantly with rheumatoid factor (RF) determined in a hemolytic assay (rs = 0.72), measured as IgG RF (rs = 0.57), and as IgM RF (rs = 0.45). There were no significant correlations with several other antibodies measured. These results are consistent with the hypothesis that RA is a systemic, extravascular immune complex disease, in which RF immune complexes play a significant pathogenetic role principally via activation of the classical pathway of complement.
mesh_terms: D000328:Adult; D000368:Aged; D000974:Antibodies, Antinuclear; D000936:Antigen-Antibody Complex; D000961:Antilymphocyte Serum; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D003180:Complement C3b Inactivator Proteins; D003181:Complement C4 / Q000096:biosynthesis / Q000378:metabolism*; D011415:Complement Factor B / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011234:Precipitins; D012217:Rheumatoid Factor / Q000276:immunology*
chemical_list: D000974:Antibodies, Antinuclear; D000936:Antigen-Antibody Complex; D000961:Antilymphocyte Serum; D003180:Complement C3b Inactivator Proteins; D003181:Complement C4; D004792:Enzyme Precursors; D011234:Precipitins; D012217:Rheumatoid Factor; D011415:Complement Factor B