The detection of circulating immune complexes containing C1q and IgG using a new rapid serum ELISA test system

An ELISA sandwich assay for detecting circulating immune complexes (CIC) was evaluated. Heat-aggregated IgG (HAG) containing Clq (HAG:Clq) is used to generate standard curves for quantitation of CIC. Sera from 488 normal donors had an means of 3.8 +/- 15.3 micrograms/ml HAG eq and 97.1% had concentrations less than 35 micrograms/ml HAG eq (2 SD greater than means) and were considered negative. Sera from rheumatoid arthritis (RA) patients in active disease tested 86% positive for CIC (means = 104.5 +/- 63.4 micrograms/ml HAG eq) while 100% with inactive disease were negative (means = 11.4 +/- 3.7 micrograms/ml HAG eq). Similarly, in systemic lupus erythematosus (SLE) patients with active disease, 100% were positive (means = 133.1 +/- 50.6 micrograms/ml HAG eq) while 80% with inactive disease were negative (means = 20.4 +/- 21.4 micrograms/ml HAG eq). In AIDS (AIDS related), 88.5% of AIDS sera and 77.1% of lymphadenopathy syndrome (LAS) sera had elevated CIC. Sera from asymptomatic homosexual controls showed 85% positive for CIC. The serum ELISA test for CIC compared favorably with the 125I-staphylococcus binding assay but was more sensitive than the 125I-C1qBA. The OKT4/OKT8 ratios were also significantly reduced in AIDS and LAS.