Anti-thyroxine and anti-triiodothyronine antibodies in three cases of Hashimotos thyroiditis.

Antibodies against thyroxine (T4) and/or triiodothyronine (T3) were detected in 3 patients with Hashimoto's thyroiditis. One of the patients had both anti-T4 and anti-T3 antibodies and the other 2 patients had only anti-T3 antibody. Serum T4 or T3 antibodies and the other 2 patients had only anti-T3 antibody. Serum T4 or T3 values measured by the single antibody radioimmunoassay (RIA), were low or nil in these patients. One patient was mildly hypothyroid. The other 2 patients were clinically euthyroid, but they were considered latent hypothyroid because of a slight elevation in serum TSH. On extraction of the sera with ethanol, high or normal values of T3 were obtained in all cases. Recovery of T4 or T3 added to the patients' sera determined by RIA was significantly low. The binding of [125I]T4 or [125I]T3 to the patients' sera was demonstrated by the polyethylene glycol method and by using RIA kits without adding the antibody provided. The binding activity was localized in the IgG fraction by column chromatography and by immunoprecipitation. T4- or T3-binding protein in two sera migrated in the gammaglobulin region on paper electrophoresis and was found in 7S fraction on Sephadex G-200 chromatography. In one serum containing both anti-T4 and anti-T3 antibodies, the association constants (Ka) for binding of T4 and T3 were 3.8 x 10(8) l/mol and 1.7 x 10(8) l/mol, respectively. The binding capacities in the serum were 8.2 microgram of T4 and 1.9 microgram of T3 per 100 ml of serum. For two sera containing anti-T3 antibody, Ka were 5.5 x 10(8) l/mol and 7.4 x 10(10) l/mol, and the binding capacities were 0.6 microgram/100 ml serum and 0.7 microgram/100 ml serum respectively. The clinical significance of these antibodies is discussed.