THE IMMUNODOMINANT REGION ON HUMAN THYROID PEROXIDASE RECOGNIZED BY AUTOANTIBODIES DOES NOT CONTAIN THE MONOCLONAL-ANTIBODY 47 C21 LINEAR EPITOPE/

We performed studies to determine whether the binding sites on thyroid peroxidase (TPO) of immunoglobulin antigen binding fragments (Fabs) r epresenting more than 80% of the human autoantibody repertoire overlap with the binding site of monoclonal antibody (Mab) 47, the only Mab w hose partial epitope has been defined at the amino acid level (residue s 713-721). We also investigated whether these Fabs preferentially rec ognize native or denatured TPO. None of the Fabs, when bound to radiol abeled TPO, interfered with the ability of Mab 47 to bind to this mate rial. In enzyme-linked immunosorbent assay experiments, the binding of TPO autoantibody Fabs SP1.5, WR1.7, TR1.8, and TR1.9 was greatly dimi nished by denaturation of TPO. In contrast, binding of Mab 47 was high er to denatured TPO than to intact TPO. Our studies indicate that the Mab 47/C21 epitope lies outside the immunodominant region on TPO. Furt her, the data confirm that the majority of epitopes for TPO autoantibo dies are highly conformational (dependent on the three-dimensional str ucture of the native protein). Native TPO will be needed to complete t he mapping of the epitopes for TPO autoantibodies as well as to determ ine the amino acids at the autoantibody-antigen-binding sites.