The accumulation of [35S]methimazole by human and rat lymphocytes.

The accumulation of 35S labelled methimazole (MMI) was examined in lymphocytes. No uptake of label was found in peripheral blood lymphocytes (PBL) from normal control subjects after in vitro incubation with the drug. Following administration of [35S]MMI to patients with Graves' hyperthyroidism PBL cell to plasma (C/P) 35S activity was greater than 1 in 4 of 11 patients and only in 1 of 7 other patients undergoing thyroidectomy. Thyroid lymphocytes from 2 of these patients showed some accumulation of activity. Following administration of [35S]MMI to normal rats C/P 35S ratios ranged from 1-5.6 but no 35S accumulation was found in PBL or thyroid lymphocytes from August strain rats in which experimental autoimmune thyroiditis had been produced. It is concluded that there is minimal, if any, significant accumulation of MMI in lymphocytes of patients with Graves' disease. The immunosuppressive action of MMI on lymphocyte antibody production must therefore by indirect.