Detection of antithyroglobulin autoantibodies with defined epitopic specificity by a microparticle-enhanced nephelometric immunoassay.

To hydrophilic, polyfunctional spherical microparticles of predetermined diameter, produced by copolymerization of acrylic monomers, we covalently bound human thyroglobulin. The thyroglobulin-microsphere conjugate was agglutinated, in the presence of antimouse immunoglobulins antiserum, by four monoclonal antibodies, each recognizing a different antigenic domain on the thyroglobulin molecule. These agglutinations were quantified by measuring with a specially designed nephelometer the light scattered by clusters of the conjugates. Agglutination with the monoclonal antibody recognizing antigenic domain II of the thyroglobulin molecule was specifically inhibited by some human sera that contained antithyroglobulin autoantibodies. This allowed us to develop a microparticle-enhanced nephelometric immunoassay for these autoantibodies with defined epitopic specificity. Using this assay, we detected and quantified antithyroglobulin autoantibodies in serum samples from all eight patients examined with Hashimoto disease and from most (75%) patients with untreated Graves disease.