Circulating immune complex-like materials which bind to heat inactivated C1q interfere with the C1q solid phase assay for immune complexes.
C1q solid phase assay (C1q SP) was devised based on the fact that immune complexes (IC) and aggregated human globulin (AHG) bind to C1q. Neither IC nor AHG was found to bind to heat inactivated C1q. On the other hand, circulating immune complex (CIC)-like materials in patients' sera were able to bind to heat inactivated C1q, indicating that these CIC-like materials are not true CIC. Gel filtration analysis showed that molecular size of such CIC-like materials was almost the same as monomeric IgG, while true CIC were in heavy fractions. True CIC did not bind to heat inactivated C1q but bind only to native C1q. The CIC-like activity is not due to rheumatoid factors. About 2/3 of CIC positive sera by C1q-SP are not really CIC positive but are due to interference by the CIC-like materials.
D000818:Animals; D000936:Antigen-Antibody Complex / Q000032:analysis*; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D003166:Complement Activating Enzymes / Q000276:immunology*; D015922:Complement C1q; D005921:Glomerulonephritis / Q000276:immunology; D006358:Hot Temperature; D006801:Humans; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000276:immunology; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D011817:Rabbits
D000936:Antigen-Antibody Complex; D007074:Immunoglobulin G; D015922:Complement C1q; D003166:Complement Activating Enzymes