Epitope binding of human thyroglobulin autoantibodies of different IgG subclasses.

Autoantibodies against thyroglobulin in patients with Hashimoto's thyroiditis are believed to recognize only three main epitopes. The possibility that antibodies of different IgG subclass recognize these separate epitopes has been suggested by preliminary studies with monoclonal antibodies against thyroglobulin. To assess whether this is a more general phenomenon, sera from 9 Hashimoto patients were fractionated into subclasses IgG1, IgG2 and IgG4 by negative selection on affinity columns. Binding of each subclass to thyroglobulin both in a competition ELISA and an assay of radiolabelled thyroglobulin immunoprecipitation was significantly inhibited by the other subclasses. These results indicate that there is no restriction of thyroglobulin epitope recognition by different IgG subclasses in unselected patients with autoimmune thyroiditis.