Qualitative testing for circulating immune complexes by use of zone electrophoresis on agarose.

On binding of antibody to antigen an immune complex is formed that has a net surface charge different from that of either of the two components. This, together with clonal restriction of the antibody response, gives rise to distinctive patterns that are readily apparent in stained agarose gels after routine zone electrophoresis. Most circulating immune complexes appear as a rectangular pattern, with well-defined edges, located in the gamma-region. The identity of the material responsible for these patterns has been established by three different experimental approaches: analysis of tetanus/anti-tetanus complexes formed in vitro, analysis of sera from rabbits with experimental immune complex disease, and analysis of human type II and type III cryoglobulins. Studies of reproducibility, interfering substances, and correlation with other assays for detecting immune complexes indicate that zone electrophoresis in agarose gel is a sensitive, highly specific technique for immune complex detection, of potential value as a screening tool.