Regulation of vitamin D homeostasis: implications for the immune system

Vitamin D homeostasis in the immune system is the focus of this review. The production of both the activating (25- and 1 alpha-hydroxylase) and the metabolizing (24-hydroxylase) enzymes by cells of the immune system itself, indicates that 1,25(OH)(2)D-3 can be produced locally in immune reaction sites. Moreover, the strict regulation of these enzymes by immune signals is highly suggestive for an autocrine/paracrine role in the immune system, and opens new treatment possibilities. (C) 2008 International Life Sciences Institute.