From a public release and summary on March 7 of a forthcoming article in Nature Immunology; Vitamin D controls T cell antigen receptor signaling and activation of human T cells, by Carsten Geisler et al of the University of Copenhagen:
Scientists at the University of Copenhagen have discovered that Vitamin D is crucial to activating our immune defenses and that without sufficient intake of the vitamin, the killer cells of the immune system – T cells – will not be able to react to and fight off serious infections in the body.
Caption: When the naïve T cell recognizes foreign molecules with its T cell receptor (TCR) it sends activation signals (1) to the VDR gene. The VDR gene now starts the production of VDR (2). VDR binds vitamin D in the T cell (3) and becomes activated. Vitamin D bound to activated VDR goes back into the cell nucleus and activates the gene for PLC-gamma1 (5). PLC-gamma1 is produced (6) and the T cells can get started.
Professor Carsten Geisler from the Department of International Health, Immunology and Microbiology explains that ”when a T cell is exposed to a foreign pathogen, it extends a signaling device or ‘antenna’ known as a vitamin D receptor, with which it searches for vitamin D. This means that the T cell must have vitamin D or activation of the cell will cease. If the T cells cannot find enough vitamin D in the blood, they won’t even begin to mobilize. ”
Telegraph.co.uk; Vitamin D ‘triggers and arms’ the immune system
Scientific Amercan; Another reason vitamin D is important: it gets T cells going
Wikipedia; Immune System
Köbenhavns Universitet: D-vitamin er helt afgørende for immunforsvaret