COMPARISON OF 5 ASSAYS FOR IMMUNE-COMPLEXES IN THE RHEUMATIC DISEASES - PERFORMANCE-CHARACTERISTICS OF THE ASSAYS

Abstract

The BCA [bovine conglutinin assay], the 125C1qBA [complement C1q binding assay], the mRF [monoclonal rheumatoid factor] inhibition assay, Raji [human Burkitt''s lymphoma] cell assay and the SBA [staphylococci binidng assay], all assays for IC [immune complex], were evaluated for their performance characteristics on the same specially prepared samples (267 [human] sera), and results were compared by reference to a common standard. Differences in reproducibility between the test were relatively consistent regardless of the parameter of variation examined or the internal standard used to compute results (overall rank over of variation:BCA and SBA < C1qBA and Raji < mRF). Larger IC were overestimated, and smaller IC were underestimated, by the assays. Intermediate (11-19s) complexes were detected by all the assays, but there were marked differences in sensitivity for this material (SBA > mRF > BCA > Raji > C1qBA). The correlation of IC assay results with IgG levels in clinical specimens could not be reproduced in vitro with monomeric IgG, and, thus, an artifactual influence of IgG levels on IC assay readouts was not the primary reason for this correlation. All assays were influenced by the presence of IgM rheumatoid factors. The effect of other serum manipulations, such as polyanions, anticoagulants and variation in complement, could have been predicted from the receptor principle of each assay.