Effects of antithyroid drugs on lymphocyte proliferative responses to lectins: relationship between insulin autoimmune syndrome and methimazole.

Using peripheral blood lymphocytes from 8 healthy individuals and 5 patients with untreated Graves' disease, direct effects of methimazole (MMI) and propylthiouracil (PTU) on lectin-induced lymphocyte proliferative response were studied. Lymphocytes were cultured for 72 hr in the presence of lectins and antithyroid drugs. Lymphocyte DNA synthesis was counted by incorporation of 3H-thymidine. MMI at 1,000 microM enhanced lectin-induced lymphoproliferation of peripheral blood lymphocytes from both patients with Graves' disease and healthy individuals, at every point of culture time, while PTU showed a tendency toward suppression. These results suggest that this lympho-stimulation by MMI may be a causative factor related to insulin autoimmune syndrome, as deduced from the clinical reports that insulin autoimmune syndrome is, sometimes, found in patients with Graves' disease treated with MMI. This lympho-stimulation was evident regardless of the time of MMI addition, thus indicating that MMI is, by its action, a lymphoid stimulator and may lead to the insulin autoimmune syndrome in predisposed subjects with underlying Graves' disease.