The detection of complement binding immune complexes by means of 51Cr-labelled indicator cells.

A radioimmunoassay is described for the detection of circulating complement binding immune complexes. The method was found to be highly sensitive but of limited specificity. It is based on the ability of the complexes to bind added complement (C1q-component) so that they are not available for the lysis of 51Cr-labelled chicken red blood cells in a haemolytic system. Sera from 241 patients and 87 healthy persons were studied for the presence of circulating immune complexes. The complement binding capacity is dependent on the disease groups. Patients with immune complex diseases showed a high significant difference to the healthy persons. The experimental conditions and the quality control of the method were described. There was found a very good correlation between complement binding capacity and concentration of heat-aggregated immunoglobulin.