Circulating Immune Complexes in the Serum in Systemic Lupus Erythematosus and in Carriers of Hepatitis B Antigen QUANTITATION BY BINDING TO RADIOLABELED Clq

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Abstract

A sensitive and reproducible procedure for the detection of soluble immune complexes in sera from patients with various immunopathological disorders is reported. Radiolabeled C1q is reacted with sera containing immune complexes. Separation of free from complex bound [125I]C1q is achieved by selective precipitation with polyethylene glycol (PEG). The method is based on both the large molecular size and the C1q-binding property characterizing immune complexes. The minimal amount of aggregated immunoglobulins thus detected is about 10 μg and that of soluble human IgG-anti-IgG complexes is about 3 μg of complexed antibody. Some immune complexes formed in large antigen excess (Ag2Ab) can still be detected by this radiolabeled C1q binding assay. The specificity of the radiolabeled C1q binding test was documented by the inability of antigen-F(ab′)2 antibody complexes to lead to a precipitation of [125I]C1q in PEG.

Authors

Urs E. Nydegger, Paul H. Lambert, Heidi Gerber, Peter A. Miescher