Antithyroid drugs inhibit in vivo HLA-DR expression in thyroid follicular cells in Graves' disease

Antithyroid drugs have been reported to reduce the expression of HLA-DR in thyrocytes in Graves' disease, but only circumstantial evidence has been pr ovided about their ill vivo immunologic effects. This present study was des igned to examine the in vivo immunologic effect of antithyroid drugs on thy roid follicular cells. The study was conducted on 25 patients who had Grave s' disease in remission or in activity and who were or were not receiving t reatment (7 in overt thyrotoxicosis, 6 patients in remission, and 12 patien ts under medication). HLA-DR expression in thyroid biopsies was verified by immunohistochemistry. The follicular cells of all patients in overt thyrot oxicosis expressed HLA-DR whereas those of patients in remission were negat ive for HLA-DR. HLA-DR was also not expressed in all patients under medicat ion, but this did not correlate with the clinical evolution after thyroid d rug withdrawal. In conclusion, antithyroid drugs inhibit follicular cell HL A-DR expression in Graves' disease, when thyrotoxicosis is controlled. This suggests that additional mechanisms not involving HLA-DR play a role in th yroid autoimmune disease.