Microparticle-enhanced nephelometric immunoassay of anti-thyroid peroxidase autoantibodies in thyroid disorders.

Crude thyroid peroxidase extracted from human thyroid microsomes was covalently bound onto polyacrylic and polyfunctional copolymerized microparticles. We observed agglutination of the thyroid peroxidase-microparticle conjugate with 13 monoclonal antibodies (mAbs) specific for epitopes on four different antigenic domains of human thyroid peroxidase (TPO; EC 1.11.1.7), after addition of anti-mouse immunoglobulins. We quantified agglutination by measuring with a specially designed nephelometer the light scattered by the conjugates. This allowed us to develop a microparticle-enhanced nephelometric immunoassay for human anti-TPO autoantibodies (aAbs) with defined epitopic specificity, based on the ability of aAbs to inhibit mAb-induced agglutination. Applied to patients with autoimmune thyroid diseases, this assay confirmed the polyclonality of anti-TPO aAbs and their preferential reactivity toward epitopes located on the A and B antigenic domains of the TPO molecule. The same specificities seem to be present in patients with Hashimoto thyroiditis or Graves disease.