Circulating soluble IL-2 receptor levels are low in patients with hypothyroid autoimmune thyroiditis

In hypothyroid patients serum soluble IL-2 receptor levels showed scattered and conflicting results. In our report we studied circulating soluble interleukin 2 receptors in 22 patients with hypothyroid autoimmune thyroiditis before L-thyroxine treatment and when the patients became euthyroid. The mean of soluble Interleukin 2 receptor levels in the hypothyroid state was 48.6 pmol/l (95% confidence interval, 45.6-51.5) statistically lower than in the controls (95% confidence interval, 86.4 pmol/l, 83.3-89.4) (p < 0.0001). When the patients became euthyroid during L-thyroxine treatment, soluble Interleukin 2 receptor levels increased, showing mean values comparable to the controls. A positive high correlation (p < 0.001) was observed between soluble Interleukin 2 receptor levels and thyroxine free levels in the hypothyroid as well as in the euthyroid state and between soluble Interleukin 2 receptors and the mean weekly L-thyroxine dose. Our study confirmed that in the hypothyroid state, the behaviour of soluble Interleukin 2 receptors is anomalous as compared to other autoimmune diseases. In fact a strict relationship exists between the levels of thyroid hormones and soluble Interleukin 2 receptors but not between the latter and antithyroid antibodies. These results agree with those supporting a role for thyroid hormones in the regulation of the immune system. They also suggest that the measurement of soluble Interleukin 2 receptors could be used as a marker of the peripheral action of thyroid hormones.