Evaluation of anti-C1q capture assay for detecting circulating immune complexes and comparison with polyethylene glycol-immunoglobulin G, C1q-binding, and Raji cell methods.
An anti-C1q capture method kit (C1q-immunoglobulin G [IgG]) (Ortho Diagnostics, Inc., Raritan, N.J.) for measuring circulating immune complexes (CIC) was evaluated. The kit showed poor diagnostic sensitivity (P less than 0.005) for identifying CIC in patients with systemic lupus, rheumatoid arthritis, and bacterial endocarditis, as compared with polyethylene glycol-IgG and Raji cell tests (12, 24, and 24 positive, respectively, of 31 patients). Of the patients who were positive with the C1q-IgG test, 25% showed discrepancies when their results were compared with the polyethylene glycol-IgG and C1q-binding test results. Gel filtration chromatography of two of these discrepant sera showed the only peak of C1q-IgG activity to be associated with monomeric IgG (molecular weight, less than 200,000). We concluded that the kit method may be measuring substances other than CIC in some sera, because molecules of C1q attached to IgG should exhibit a molecular weight of greater than 500,000.
D000936:Antigen-Antibody Complex / Q000032:analysis*; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000276:immunology; D002460:Cell Line; D002850:Chromatography, Gel; D003166:Complement Activating Enzymes; D003172:Complement C1; D015922:Complement C1q; D004698:Endocarditis, Subacute Bacterial / Q000175:diagnosis* / Q000276:immunology; D006801:Humans; D007105:Immune Complex Diseases / Q000175:diagnosis* / Q000276:immunology; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G; D008180:Lupus Erythematosus, Systemic / Q000175:diagnosis* / Q000276:immunology; D011237:Predictive Value of Tests; D011933:Reagent Kits, Diagnostic
D000936:Antigen-Antibody Complex; D003172:Complement C1; D007074:Immunoglobulin G; D011933:Reagent Kits, Diagnostic; D015922:Complement C1q; D003166:Complement Activating Enzymes