Anti Thyroid Hormone Autoantibodies under Experimental and Clinical Conditions

Abstract

Autoantibodies against thyroid hormones were experimentally induced and clinically observed. Rats were immunized with a single dose of T₃-conjugate, T₄-conjugate or both. Six months later total T₃ and total T₄ were measured by radioimmunoassays after alcohol extraction as well as TSH in rats (rTHS). Also antibody titers against T₃ and T₄ were determined. Oxygen consumption of immunized and control rats was measured in special metabolic cages. After immunization T₃ and/or T₄ concentrations were markedly elevated in close correlation to the respective antibody titers. rTSH was not changed. Oxygen consumption was not altered in immunized animals, whereas thiamazol treated rats showed diminished oxygen consumption indicating decreased basal metabolic rate. Clinically occurring thyroid hormone autoantibodies can be detected by RIA using charcoal separation for bound and free hormone since they result in high unspecific binding. Such sera are subjected to antibody titer determination and total T₃ and T₄ are measured after alcohol extraction. T₃ autoantibodies were observed in euthyroid and hyperthyroid sera, and their titers were again correlated to total T₃ concentrations. It can be concluded, that the increased total hormone concentrations in antibody positive sera are biologically irrelevant, since rTSH and oxygen consumption were normal suggesting normal free hormone concentrations. In patients with thyroid hormone autoantibodies the diagnosis cannot be made from total hormone concentrations or antibody titers, but must be made on the basis of clinical appearance and TRH tests.