Anti-IgGBindingTest to AssayCirculatinglgG-ContainingImmune Complexesfrom PolyethyleneGlycolPrecipitates

We describe a simple approach for assaying immune complexes from serum by usinganti-lgG as the indicatorafter a three-step extraction procedure with polyethylene glycol. Analysisof the data indicatesthat assaysof suchextractsfor 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 Clq-binding test. The present assay and the Raji cell test were more sensitive than the Clq-binding test (p < 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 immunoassaytechniques.