Plasma interleukin-2 levels and thyroid function in elderly patients with nonthyroidal illness.

To determine whether interleukin-2 (IL-2) plasma concentrations are modified in patients with nonthyroidal illness (NTI) and thyroid function alterations, we measured plasma concentrations of T(3), T(4), free T(3) (FT(3)), free T(4) (FT(4)), TSH, and IL-2 in 34 elderly NTI patients and in 25 age- and sex-matched healthy controls. IL-2 was detectable in 11 of the 34 patients. Patients with detectable IL-2 plasma levels had significantly lower plasma T(3) and FT(3) concentrations when compared to those with undetectable IL-2. Moreover, IL-2 plasma levels were positively correlated to reverse T(3) (rT(3)), (r(S)=0.67, P<0.05), and negatively to FT(3) concentrations (r(S) =-0.64, P<0.05). These observations suggest that some of the alterations in thyroid hormone levels seen in NTI are associated with elevated plasma concentrations of IL-2.