Methodological approaches to antigen identification in soluble immune complexes; A model study.

The usefulness of different techniques for identification of immune complex-(IC) bound antigen(s) was investigated in two Ab-Ag model systems. The following approaches were used: 1) determination of IC-activity before and after removal of IC by adsorption to antibody-specific solid phase systems, 2) analysis of PEG-insoluble IC by reference line-rocket Immunoelectrophoresis and 3) reprecipitation of PEG-insoluble IC in the presence of 125I-labelled antibody to suspected antigens and subsequent analysis of the distribution of the radioactivity. This latter approach, the use of a double PEG precipitation immunoradiometric assay, was found most useful and simple for identification of antigen(s) contained in soluble IC. The technique is most sensitive in demonstrating IC-bound antigen(s) when the IC are formed in slight to moderate antigen excess.