The role of thyroid hormone autoantibodies in serum transport

Eleven sera known to contain thyroid hormone autoantibodies were analysed by reverse-flow electrophoresis for the equilibrium distribution of thyroid hormones between these autoantibodies and the three normal binding proteins found in serum. The binding properties of the autoantibodies determined in vitro did not necessarily predict their contribution to transport in serum of T1 and T3. Some could both bind in vitro and transport in serum. Others were able to bind both hormones but transported only one. However, some autoantibodies could be specific, binding and transporting one hormone only. In some sera, the autoantibody was the dominant transport protein having drawn hormone from thyroxine-binding globulin which is normally the most important. The autoantibodies were not saturated even in euthyroid individuals, indicating that they bind hormone reversibly and are a part of an equilibrium system.