Anti-IgG binding test to assay circulating IgG-containing immune complexes from polyethylene glycol precipitates

We describe a simple approach for assaying immune complexes from serum by using anti-IgG as the indicator after a three-step extraction procedure with polyethylene glycol. Analysis of the data indicates that assays of such extracts for immune complexes by absorbance nephelometry, kinetic light scatter, and immunoradiometric techniques correlate well. For 116 samples, results by absorbance nephelometry correlated (r = 0.86) with those by the C1q-binding test. The present assay and the Raji cell test were more sensitive than the C1q-binding test (p less than 0.001) for detecting increased concentrations of immune complexes in 29 samples from patients with immune-complex-type diseases. The basic approach we describe may lend itself to broad applications for use with various immunoassay techniques.