Effects of antithyroid drugs on lymphocyte function in vitro

The in vitro influence of 6-propylthiouracil (PTU) and methimazole (MMi) on mitogenic activation of human peripheral blood lymphocytes was studied in order to assess whether antithyroid drugs may have an immunomodulatory capacity. Lymphocytes were cultured for 72 h in the presence of phytohaemagglutinin (PHA; 1.25 microgram/ml), concanavalin A (Con A; 5.0 microgram/ml), or pokeweed mitogen (PWM; 2.5 microgram/ml). Antithyroid drugs were added to yield final concentrations of 1-1000 mu mol/liter. High pressure liquid chromatographic analyses verified that the expected drug concentrations in the incubation media were reached and maintained throughout the incubation period. The degree of lymphocyte activation was assessed by measurements of the cellular uptake of [3H]thymidine added after 48 h. PTU (at 1000 mu mol/liter) slightly suppressed PHA- and Con A-induced activation of lymphocytes but enhanced (at 5-500 mu mol/liter) PWM-induced activation. MMI (500-1000 mu mol/liter) enhanced not only PWM-induced activation but (at 1000 mu mol/liter) also enhanced PHA- and Con A-induced activation. Thus, PTU and MMI might interfere with mitogenic activation of lymphocytes. However, the effects were mainly recorded at drug concentrations exceeding those found in blood samples of patients treated with conventional doses.