Effect of 1,25-dihydroxyvitamin D3 on cytokine-induced thymocyte proliferation

To clarify the mechanism of the inhibitory effect of 1,25(OH)2D3 on lymphocyte proliferation, the effect of 1,25(OH)2D3 on murine thymocyte proliferation induced by interleukin 1 (IL-1), or 2 (IL-2) was examined. Physiological concentrations of 1,25(OH)2D3 inhibited thymocyte proliferation induced by IL-1 and IL-2 in similar fashion suggesting an inhibition of the response to IL-2 by this hormone. In addition, cortisone-resistant thymocytes (including a majority of medullary thymocytes), which proliferate more vigorously in response to IL-1 than do untreated thymocytes, were more sensitive to 1,25(OH)2D3 inhibition. Therefore, the inhibition of IL-2 production of the mature medullary thymocyte by this hormone was also suggested.