A polyclonal IgM-RF enzyme-linked immunosorbent assay for the detection of circulating immune complexes

A microplate-adapted polyclonal IgM-rheumatoid factor enzyme-linked immunosorbent assay (pIgM-RF ELISA) for the detection of circulating immune complexes (cIC) is presented. The assay involves the competitive binding of cIC and horseradish peroxidase conjugated aggregated human IgG (HRP-AHG) to solid-phase bound polyclonal IgM-RF (pIgM-RF). Aggregated human IgG (AHG) inhibited the binding of HRP-AHG to pIgM-RF in a dose-dependent way. The detection limit of the assay was about 125 ng AHG/ml diluted serum. The coefficients of variation for the assay varied from 5.0 to 14.7% for intra-assay runs and from 4.5 to 13.8% for inter-assay runs. The levels of cIC in sera from 29 patients with systemic lupus erythematosus (SLE), 85 untreated patients with breast cancer and 105 blood bank donors were studied by the pIgM-RF ELISA. Increased levels of cIC were demonstrated in 41.4% of the SLE group, in 8.2% of the breast cancer group, and in 1.9% of the normal control group. The difference in cIC activity between the SLE group and the normal control group was statistically significant.