Effects of thyroid hormones on the lymphocyte phenotypes in rats: changes in lymphocyte subsets related to thyroid function.

The effects of hyperthyroidism and hypothyroidism on the immune function were assessed in rats by the changes in lymphocyte subsets in peripheral blood and spleen. Hyperthyroidism was induced in rats by intraperitoneal injection of large doses of T4. Hypothyroid rats were prepared by total thyroidectomy followed by 131I administration. In the hyperthyroid rats, the peripheral blood helper/suppressor T cell ratio was decreased, while in hypothyroidism this ratio was increased. However, in spleen cells, this ratio was increased in hypothyroid rats as compared to normal controls. The most striking finding was an augmentation of activated T cells (transferrin receptor positive lymphocytes) in both peripheral blood and spleen cells in the hypothyroid rat. These results suggested that thyroid hormone suppressed the immune response and that a deficiency of this hormone was associated with an increase of activated T cells. These effects of thyroid hormone on the lymphocyte subsets in rats were at variance with the abnormalities that have been observed in humans with such autoimmune thyroid disease as Graves' disease.