The use of the preparation of F(ab')2 antibody from soluble immune complexes to determine the complexed antigens.

An autoradiographic technique for the characterization of antibody specificity in soluble antigen--antibody complexes has been developed. The circulating antigen--antibody complexes are precipitated by polyethylene glycol (PEG). The antibodies are liberated as F(ab')2 from the complexes by pepsin digestion. The antibody specificity against the putative antigen was revealed by radioimmunoelectrophoresis using [125I]-F(ab')2 reagents. The method was developed by using an experimental model of C3/anti-C3 complexes.