AN AUTOIMMUNO-DOMINANT THYROGLOBULIN EPITOPE CHARACTERIZED BY A MONOCLONAL-ANTIBODY

It has become evident in recent years that autoimmune thyroglobulin (Tg) antibodies of Graves' disease and Hashimoto's thyroiditis show a restricted epitope repertoire compared to Tg heteroantibodies. We have produced monoclonal antibodies (Mab) against human Tg by the hybridoma technique and the epitope specificity was determined by crossblocking experiments. Six noncrossreactive Mabs were used in a double determinant IRMA system for plasma Tg measurements. Sensitivity of the assays was between 1 and 2 ng/ml, intraassay variation less than 5%. Recovery experiments with added Tg were performed in 25 Graves' sera with elevated Tg autoantibodies. Monoclonal antibody Tg13 showed an unusual strong interference with autoantibodies resulting in a very low recovery in all sera (median: < 10%). In further studies Tg was digested by trypsin and after Western blotting, the resulting fragments were incubated with different Mab antibodies, a polyclonal antibody and 10 different Graves' sera with high Tg autoantibodies. In contrast to all other mabs only Mab Tg13 showed several low molecular weight bands between 17 and 50 KD. The major bands recognized by Mab Tg13 corresponded to bands obtained by the autoimmune sera, which showed a very homogeneous band pattern. We conclude that Mab Tg13 is specific for an autoimmunodominant B cell epitope of human Tg.