Characterization of soluble circulating immune complexes by antigen-specific dissociation: detection in the Raji cell radioimmune assay.

The Raji cell radioimmune assay (RC-RIA) was used to demonstrate antigen-mediated dissociation of soluble circulating immune complexes (CICs). The dissociation resulted in a reduction in size and number of CICs which was reflected in diminished RC-RIA activity. Two sets of experiments were performed to examine the effect of preincubating excess antigen with immune complexes. First, bovine serum albumin (BSA) was preincubated with preformed BSA-anti-BSA immune complexes and RC-RIA activity was examined before and after incubating. Second, CIC-positive sera from two patients with human thyroglobulin (HuTg)-mediated immune complex glomerulonephritis were preincubated with HuTg and RC-RIA activity was examined. Significant reductions in RC-RIA activity were seen in both situations. The validity of these observations was confirmed by immunofluorescence and electrophoretic techniques. Sucrose density gradient ultracentrifugation studies confirmed the antigen-mediated diminution in size and number of soluble immune complexes as the mechanism responsible for diminished RC-RIA activity.