Triiodothyronine enhances expression of the interleukin-2 receptor alpha chain.

The effect of thyroid hormone on immune function is unclear. The influence of L-triiodothyronine on expression of the interleukin-2 receptor alpha chain by peripheral blood mononuclear cells from healthy volunteers and YT cells (an interleukin-2 independent natural killer-like cell line) was examined. Concanavalin A stimulation significantly (p<0.05 and p<0.01) increased soluble interleukin-2 receptor alpha chain production when mononuclear cells were cultured with triiodothyronine (1-100 nmol/l) for 3 days. The stimulatory effect of triiodothyronine on interleukin-2 receptor alpha chain expression was greater in the presence of concanavalin A (5 microg/ml) plus interleukin-2 (1 U/ml) than in the presence of concanavalin A alone. Triiodothyronine also significantly (p<0.01) increased interleukin-2 receptor alpha chain expression when YT cells were cultured for 2 days with interleukin-2 (1 U/ml), but did not influence receptor expression when YT cells were cultured with forskolin or 12-O-tetradecanoyl phorbol 13-acetate, potent activators of signal transduction. In conclusion, triiodothyronine may have an immunomodulatory effect by enhancing expression of the interleukin-2 receptor alpha chain on peripheral blood mononuclear cells in the presence of interleukin-2.