NEPHROTIC SERUM CONTAINS A SUBSTANCE WHICH INHIBITS THE DETECTION OF IMMUNE COMPLEXES

Abstract

Serums from 17 patients with idiopathic nephrotic syndrome were examined for immune complexes by a solid phase Clq radio-immunoassay. No serum had elevated C1q binding. Instead, the nephrotic serums contained a factor which inhibited the binding of monomeric IgG, aggregated IgG, and naturally occurring IgG immune complexes to C1q. As a result of this inhibition the amount of immune complex material in nephrotic serum is underestimated by the solid phase C1q radioimmunoassay. The inhibition could not be accounted for by the reduced levels of Clq or IgG in the nephrotic serums, nor by hyperlipemia, nor by IgM or IgM containing immune complexes. The factor did not bind to C1q. Serum from patients with idiopathic nephrotic syndrome contains a substance which binds to IgG and reduces the affinity of IgG for C1q. Immune complex assays which rely upon the interaction of complexes with C1q give falsely low values in these individuals.