A solid-phase, polyclonal IgM-RF binding assay for circulating immune complexes.

Abstract

A polyclonal IgM-RF-binding assay (pRF-BA) for the detection of circulating immune complexes (IC) is described. The method is based on the competitive binding of heat-treated iodinated IgG (deltaIgG) and naturally occurring IC to solid phase IgM-RF. The sensitivity limit of the assay was 300--400 ng deltaIgG/ml dilute serum. The coefficient of variation for the assay varied from 6 to 12% of the total binding when deltaIgG concentrations up to 1 microgram/ml were measured. One hundred and six patient sera were examined for IC occurrence and significant differences (p less than 0.01) were observed between 30 normal control sera and sera from SLE, sarcoidosis and glomerulonephritis patients. About 40% of patients suffering from acute myocardial infarction (AMI) gave IC-positive reactions with samples taken 5 to 10 days after the infarction. The kinetics of IC appearance was studied in AMI patients by the pRF-BA and three complement-dependent assays. IC appearance was registered in the RF assay 5 to 12 days after the rise in ASAT enzyme values and the IC reactivity corresponded to complexes ranging from 2 to 5 x 10(6) in molecular weight.