THYROXINE BINDING TO ANTITHYROID ANTIBODIES: EFFECTS OF ALTERED METABOLIC STATUS

Abstract

SUMMARY Thyroxine-binding antithyroid antibodies produced by hetero- or isoimmunization were examined in animals in different metabolic conditions. Guinea-pigs and rats were treated with thyroxine (T4) or methimazole or kept at 4 °C. During treatment they were immunized with heterologous or isologous thyroid extracts. Control animals were given liver extracts or saline. Rabbits were hetero- or iso-immunized but otherwise were untreated. All thyroid-immunized animals had a significantly higher level of tracer thyroxine binding in the globulin fraction of serum than had controls, regardless of metabolic status. Only thyroid hetero-immunized animals showed anti-thyroid antibodies as measured by routine immunological tests. In serum from animals with high levels of T4, less tracer was bound in the globulin fraction. This change did not represent a decrease in the amounts of T4 bound by the antibodies, but rather a redistribution of the hormone in the serum proteins. Methimazole decreased not only the specific thyroxine binding by the antithyroid antibodies but also the non-specific binding in the globulin fraction of control serum. Adaptation to cold apparently did not affect the thyroxine binding to the antibodies.