Effects of developmental hypothyroidism induced by maternal administration of methimazole or propylthiouracil on the immune system of rats.

Methimazole (MMI) and propylthiouracil (PTU) are popularly used antithyroid drugs (ATDs) for the treatment of Graves' hyperthyroidism. The aim of the present study was to determine the effects of ATDs on the developing immune system of the rats. Maternal Sprague-Dawley rats were given drinking water containing 200 ppm of MMI, 12 ppm of PTU (high-dose PTU), or 3 ppm of PTU (low-dose PTU) between gestational day (GD) 10 and postnatal week (PNW) 3. Exposure to the ATDs was ceased upon weaning at PNW3, and the male offspring were sampled at PNWs 3 or 11. The serum thyroid-related hormone levels and the hematological components in the offspring were then determined. The expressions of surface markers in the spleen, thymus and peripheral blood were determined using flowcytometry. The weights of the body, spleen and thymus and the splenic and thymic cell numbers were decreased in the MMI-treated and the high-dose PTU-treated animals at PNWs 3 and 11. The serum levels of thyroid-related hormones were depressed in the MMI and high-dose PTU groups. FACS analysis revealed that the ATDs caused proportional changes in the lymphoid cell subpopulations. The proportion of B cells among the total lymphocytes was significantly decreased at PNW3, whereas that of T cells, especially of inactive T cells, was dramatically increased. Moreover, the proportion of CD4(+)CD25(+) regulatory T cells was significantly increased in the spleen and peripheral blood at PNW3. Most of the above-described changes had recovered to normal levels at PNW11. These results suggest that ATDs might have temporal immunomodulatory effects on the developing immune system.