Quantitation of immune complexes by competitive inhibition of binding of Clq to insoluble IgG aggregates.

An assay system for the binding of Clq to insoluble IgG aggregates was found useful for the quantitation of immune complexes in biological fluids. The assay, both easily and rapidly performed, is based on the competition of Clq binding substances with IgG aggregates. Serum from rheumatoid arthritis patients showed an increase in Clq binding substances over normal serum and this increase could be abolished by pretreatment of the serum with D-penicillamine.