An evaluation of two antigen nonspecific assays for circulating immune complexes using a model system.
Two methods of detecting circulating immune complexes (CIC) in serum, the Protein A-glass fiber filter assay (PA-GFF) and the polyethylene glycol (PEG) insolubilization assay, were compared using a model system of BSA/anti-BSA. Supernatants of the quantitative precipitin curve from extreme antigen excess through antibody excess were tested by both methods. The PEG assay detected soluble CIC in all areas where expected by comparison with the Farr Test; the filter assay did not, although it did detect aggregated globulins quantitatively. The PEG assay detected high levels of CIC in serum of rheumatoid arthritis patients and low levels in normal human serum. Postprandial samples and plasma with heparin or EDTA caused unpredictable increases in results in the PEG assay so that for best results the PEG assay should be run on serum from fasting individuals. PEG insolubilized complexes were analyzed and found to contain expected serum components. A slight modification of the original method was made and tested using two other model complex systems and known CIC-containing sera. The PEG turbidity assay it fast, easy, reproducible, and suitable for quantitating and isolating immune complexes in serum.
D000818:Animals; D000936:Antigen-Antibody Complex / Q000032:analysis* / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000276:immunology; D002417:Cattle; D011232:Chemical Precipitation; D002850:Chromatography, Gel; D000939:Epitopes; D006801:Humans; D008954:Models, Biological; D011092:Polyethylene Glycols / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D012709:Serum Albumin / Q000276:immunology; D013205:Staphylococcal Protein A / Q000378:metabolism
D000936:Antigen-Antibody Complex; D000939:Epitopes; D012709:Serum Albumin; D013205:Staphylococcal Protein A; D011092:Polyethylene Glycols