Nephelometric detection of soluble immune complexes: methodology and clinical applications.

We have developed a method for the detection of immune complexes by laser nephelometry which is simple, reproducible, suitable for automation, and generally adaptable for diagnostic testing. Light dispersion by antigen-antibody complexes in the test samples is measured after addition of polymeric buffer, which enhances the aggregation of complexes but does not significantly affect unbound immunoglobulins. The method was used to measure immune complexes formed in vitro by incubation of tetanus toxoid with serum from a rabbit previously hyperimmunized with the same antigen, and to compare the levels of immune complexes in human sera obtained from normal adults and from 37 patients with collagen vascular diseases or endocarditis. When precautions were taken to avoid interference produced by the presence of lipoproteins or by freezing of the samples, the results obtained with human sera were consistent with those expected for normal controls and for patients with conditions thought to be associated with the presence of soluble immune complexes.