DETECTION AND DIFFERENTIATION OF IMMUNE COMPLEXES AND IgG AGGREGATES BY A COMPLEMENT CONSUMPTION ASSAY

Abstract

The applicability of a complement consumption assay as a means by which to detect IgG aggregates and immune complexes in serum was examined. Both heavy (≥19S) and intermediate (11‐17S) IgG aggregates were detected and the sensitivity of the assay was ≥10 μg aggregated IgG/ml. BSA anti‐BSA complexes, formed in slight antibody excess, were detected at a BSA concentration of 200 ng/ml. NHS stored at 4°C for ≥2‐3 weeks or at ‐20°C for more than 3 months developed distinct anticomplementarity (AC). This background AC, due to IgG aggregate formation, was reduced by heating the serum at 56°C for 50 min prior to testing. A similar reduction of AC and Clq fixation was observed when IgG aggregated at 61°C or 63°C was heated further at 56°C for 50 min. The abatement of AC could not be correlated to a change in IgG aggregation size. In contrast, AC of preformed antigen‐antibody complexes was not reduced by this heat treatment.