Effects of immunoglobulins upon the interaction of thyrotropin with receptors in human fat tissue

TSH bound to human fat membranes is shown to be unusually sensitive to the addition of immunoglobulin G (IgG). Significant displacement was observed with 10 μg/ml, and 50% displacement was obtained with 50-100 μg/ml IgG prepared from control sera pooled from euthyroid subjects. It was not possible to demonstrate increased TSH displacement by IgG preparations from sera of thyrotoxic compared to that of euthyroid subjects using human fat membranes, as was demonstrable with human thyroid membranes. The increased sensitivity of fat membranes to IgG was not due to nonspecific protein interactions and is suggested to derive from interactions with Fc receptors associated with fat membranes.