Tyrosine iodination and iodotyrosyl coupling of the N-terminal thyroid hormone forming site of human thyroglobulin modulate its binding to auto- and monoclonal antibodies.

The present work was aimed at studying the interaction of autoantibodies (aAb) and monoclonal antibodies (mAb) with the N-terminal thyroid hormone forming site of human thyroglobulin (TG). Obtained by CNBr treatment of TG, the peptide (22 kDa) containing the complete major hormonogenic site of human TG was purified in three forms according to the degree of iodination and iodotyrosine coupling: the native, poorly iodinated form (n-22K), the iodinated form containing iodotyrosine but not hormone residues (i-22K) and the form containing thyroid hormone (t-22K). We report that aAb from some patients with autoimmune thyroid diseases showed significant binding to both iodinated 22 kDa forms. Furthermore, a detailed study using mAb evidenced that iodination and coupling induced changes in the antigenicity of the molecule, some occurring without direct implication of iodine or thyroid hormones. The 22 kDa peptide appears as an interesting model to study the antigenic changes induced by the structural modifications in the course of thyroid hormone synthesis. This observation could be relevant to the etiopathogenic process of thyroid autoimmune diseases.