Antithyroid drug-induced immunomodulation in Graves' disease patients

The study was so designed as to determine the effect of low to medium daily doses of methimazole (10-20 mg per day) on the number and function of different types of immunocompetent cells in peripheral blood of patients with Graves' disease administered methimazole for the treatment of hyperthyroidism. The study included 127 patients with Graves' disease divided into three groups: group I of 29 thyrotoxic patients before the beginning of treatment; group II of 73 euthyroid patients under antithyroid treatment; and group III of 25 patients who remained euthyroid 8 weeks after therapy discontinuation. In group I, the proportion of CD4+ cells, proportion and number of granulocytes, and their ingestion and microbicidity as well as monocyte phagocytic activity and ingestion were decreased. The mentioned alterations were concluded to most likely be the consequence of the underlying autoimmune process. In group II, the proportion and number of CD8+ cells were increased, while the natural killer cell activity was impaired. Granulocyte microbicidity was suppressed as compared to group I, while the granulocyte phagocytic activity was impaired as compared to normal values. Compared to normal, monocyte microbicidity and phagocytic activity were also suppressed. Monocyte ingestion was suppressed as compared to groups I and III, regardless of the patients' thyroid hormone status. Study results strongly support the hypothesis of a direct immunosuppressive effect of methimazole in patients with Graves' disease rather than the theory favoring concomitant immunomodulation due to thyroid hormone decrease.