The in vitro suppression of lectin induced 3H-thymidine incorporation into DNA of peripheral blood lymphocytes after the addition of propylthiouracil.

A possible in vitro immunosuppressive role of propylthiouracil (PTU) was investigated by culturing peripheral blood lymphocytes (PBL) from normal subjects with plant lectins in the presence of PTU added at the onset of culture or near the time of peak cell division. When added at the onset of culture PTU caused a dose-related suppression of lectin stimulated 3H-thymidine uptake with an average of approximately 50% suppression at a PTU concentration of 100 mug/ml. When added at the time of peak cell division however, marked suppression was produced by 10 mug/ml of PTU. Prolonged remissions in patients with Graves' disease treated with PTU, and possibly other anti-thyroid drugs, may thus be due to an immunosuppressive role of the drug rather than the natural evolution of the disease.