Antigen-specific detection of soluble immune complexes by a solid phase specific antibody system.

An antigen-specific immune complex assay based on the following principle has been developed: xenogeneic, antigen-specific antibodies are attached to a solid phase. During first incubation with patient's serum, immune complexes in antigen excess are bound to the xenogeneic antibody by their free antigenic determinants. In a second incubation a labeled antibody, specific for human immunoglobulins, is combined with the antibody part of the immune complex. Quantitation of the label allows the determination of the immune complexes. The principle of the method has been varied using artificial soluble immune complexes of tetanus toxoid and human anti-tetanus toxoid antibody, and immune complexes prepared by mixing patient sera containing either HBsAg or anti-HBsAg antibodies. The reliability of the results is shown by their coefficient of variation (2.5%). With the method described soluble immune complexes predominantly in slight antigen excess, which are thought to be responsible for development of immune complex disease, have been detected.