Concentrations of free thyroxine, total thyroxine, and total triiodothyronine in rabbits immunized with human thyroglobulin.

Levels of serum free thyroxine, total triiodothyronine and total thyroxine were measured in two rabbits (TG-1, TG-2) which had been immunized with human thyroglobulin and produced both anti-thyroglobulin and anti-thyroid hormone antibodies. Despite the presence of both anti-triiodothyronine and -thyroxine antibodies, levels of serum free thyroxine in serial sera obtained from a rabbit (TG-1) stayed within normal range up to 249 days after the first immunization, whereas in the other rabbit (TG-2), serum free thyroxine concentrations of serial sera declined after three immunizations and stayed at lower levels than normal range up to 249 days. Extraction of serial sera from both rabbits disclosed the presence of larger amounts of triiodothyronine and thyroxine in immune sera than preimmune sera. From these results, it is concluded that the presence of anti-thyroid hormone antibodies per se can reduce serum level of free thyroxine in rabbits.