Interaction of thyroid-stimulating antibodies with the human thyrotrophin receptor

Thyroid-stimulating antibodies (TSAb) were found to inhibit the binding of labelled thyrotrophin (TSH) to thyroid membranes in a dose-dependent manner and this effect was localized in the Fab part of the TSAb molecule. Analysis of the binding data suggested that TSAb and TSH bound to the same receptor site. Production of cyclic AMP by the thyroid membranes was stimulated by TSAb and TSAb-Fab with a similar time course to that observed with TSH. Kinetic studies indicated that the binding of TSAb to the thyroid membranes was not rate-limiting in the process of stimulation of cyclic AMP production.