Depressed natural killer activity in Graves' disease and during antithyroid medication

To investigate the natural killer (NK) cell mediated immunity in Graves' disease (GD) and the effect of antithyroid drugs upon NK cell activity, 51Cr release assay for NK cytotoxicity against K562 cells was examined in patients with GD before and during antithyroid medication and after drug withdrawal. Fifty-eight patients were divided into three groups: the untreated thyrotoxic patients (n = 33), the euthyroid patients under antithyroid treatment (n = 19) and the euthyroid patients after drug withdrawal (n = 6). The results of the three groups were compared to 23, 15 and 5 sex- and age-matched controls, respectively. The data revealed a significant NK dysfunction in the untreated hyperthyroid patients, although the number of the NK cells was not decreased. NK function was normal when patients were no longer taking antithyroid medication and in euthyroid state. However, euthyroid patients under antithyroid medication had markedly depressed NK activity, suggesting an immunosuppressive effect of the antithyroid drugs. This study demonstrated that both the hyperthyroid state and the antithyroid drugs exerted immunosuppressive effects upon the NK cells. Since such an immunosuppressive effect on NK cells might be associated with a decreased immune surveillance against tumour growth, this study implies that a long-term follow up of GD patients treated with antithyroid drugs may be indicated to guard against a possible increased incidence of malignancy.