A functional relay from progesterone to vitamin D in the immune system.

Progesterone is a steroid hormone that promotes and maintains pregnancy. Vitamin D (vit. D), another steroid hormone, regulates calcium levels and bone health among many of its functions. The two hormones play important roles also in regulating the immune system. Recently, we discovered that the vitamin D receptor (VDR) is induced in T cells by progesterone. This finding connects the function of progesterone to that of vit. D and suggests that the two steroid hormones cooperate with each other for sequential and effective regulation of the immune system. Potential implications of the regulation in health and disease are discussed.