Antithyroid Drugs Ameliorate Thymectomy-Induced Experimental Autoimmune Thyroiditis

Abstract

The possible immunosuppressive action of antithyroid drugs in vivo has been assessed using Buffalo (Buf) strain rats with thyroiditis produced by neonatal thymectomy; this model shares many features with spontaneous thyroiditis in man. Both propylthiouracil and methimazole significantly reduced the severity of thyroiditis (P < 0.01 compared to controls), irrespective of effects on thyroid status. Thyroidal O.8 (suppressor/cytotoxic) and W3/25 (helper) T-cells were reduced in number equally in treated animals, and thyroid follicular cell Ia expression was absent in a high proportion of these glands. Neither agent alone altered circulating antithyroglobulin antibody levels but there was a significant fall in antibody levels in animals treated with propylthiouracil and thyroxine. Antithyroid drugs had no effect on circulating T-cell subsets, and there was no direct suppressive action in vitro on la expression by the FRTL₅ thyroid cell line. These results provide further support for a direct action of antithyroid drugs on the autoimmune process in thyroid disease exerted in particular on the thyroid lymphocytic infiltrate.

Key Words:

• Thyroiditis
• antithyroid drugs
• immunosuppression