Increased soluble interleukin 2 receptor levels in autoimmune thyroid disease.

We measured soluble interleukin 2 receptor, a part of the Tac protein (p55), in peripheral blood to study the immunological condition of the T cell in autoimmune thyroid disease. In 26 patients with untreated Graves' disease and 7 hyperthyroid patients with Hashimoto's thyroiditis, the mean levels of soluble IL-2 receptor were both significantly higher than in normal controls (1497 +/- 649 (mean +/- SD), 641 +/- 137 vs 221 +/- 63 10(3) U/l, p less than 0.001). There was good correlation between soluble IL-2 receptor levels and blood thyroxine levels (r = 0.684, p less than 0.001) in patients with untreated Graves' disease, but no correlation of soluble IL-2 receptor with TSH-inhibitory immunoglobulins, TS-ab, thyroidal autoantibodies to thyroglobulin and thyroidal microsomal antigen was found. We thought that the level of soluble IL-2 receptor is not dependent only on immunological conditions, but also on thyroid hormone status. When T3 was administered to subjects in remission from Graves' disease and in normal controls, the soluble IL-2 receptor levels significantly increased. Moreover, the mean level of soluble IL-2 receptor in patients with toxic multinodular goitre was also significantly higher than in normal controls (411 +/- 148 vs 221 +/- 63 10(3)U/l, p less than 0.05). We conclude that the soluble IL-2 receptor levels are higher in sera of subjects with elevated levels of thyroid hormone.