[Characterization of the antigen in circulating immune complexes and application to the detection of streptococcal antigens in human infectious endocarditis].

Immune complexes from patients with subacute endocarditis were used to develop a methodology for characterization of the antigen involved in human circulating immune complexes. This model was chosen because it permits isolation of the causative agent of the streptococcal infection thought to contain the antigen present in the immune complex. A comparison was made between two methods for characterization of bacterial antigen bound to antibody. In the first, animals were immunized with purified immune complexes and the production of antistreptococcal antibodies was investigated. In the second method, a sandwich ELISA was developed, implying the double specificity of the immune complex (human immunoglobulin and streptococcal antigen). The latter method gave the best results, detecting antigen in the immune complexes of 8 out of 10 patients' sera. The application of this method to other immunopathological situations is discussed.