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 ob-served agglutination of the thyroid peroxidase-micropar-tide 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 ad-dition of anti-mouse immunoglobulins. We quantified ag-glutination by measuring with a specially designed nephe-lometer 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 pa-tients with autoimmune thyroid diseases, this assay con