Circulating soluble interleukin 2 receptor concentration is increased in both immunogenic and nonimmunogenic hyperthyroidism

High serum concentration of soluble interleukin-2 receptor (sIL-2R) is considered a reliable marker of T lymphocyte activation. It has been recently reported that sIL-2R levels are increased in untreated Graves' disease. This finding has been interpreted as the consequence of an active autoimmune state, but the relevance of the thyroid function per se was not investigated. In the present study we assayed sIL-2R by ELISA in 20 normal subjects and in a series of patients with immunogenic (Graves' disease, GD) or nonimmunogenic (toxic adenoma, TA) hyperthyroidism. Significant increased concentrations of sIL-2R were found in 46 patients with untreated hyperthyroid GD (mean +/- SD: 1,683 +/- 1016 U/ml, vs 461 +/- 186 U/ml in normal controls, p less than 0.0001) and in 21 with untreated TA (1,111 +/- 617 U/ml, p less than 0.0001 vs normals). Restoration of the euthyroid state by antithyroid drugs or 131I administration was associated with a normalization of sIL-2R (516 +/- 174 U/ml in 38 patients with GD and 365 +/- 90 U/ml in 12 with TA; p = NS vs normals and p less than 0.001 vs the untreated state for both groups). A highly significant positive correlation between serum sIL-2R and free triiodothyronine (FT3) (r = 0.724, p less than 0.0001) or free thyroxine (FT4) (r = 0.698, p less than 0.0001) concentrations was found in combined sera obtained from all untreated and treated patients, irrespectively of the autoimmune or nonautoimmune nature of the underlying hyperthyroid disease