Why Vitamin D is Necessary for Adaptative Immune Response

As Rode von Essen and colleagues explain in their study published in Nature Immunology Vitamin D modulates the antigen sensitivity of T cells, especially naive T cells, through their vitamin D receptor. The vitamin D receptor regulates the expression of a type of enzyme in the cytoplasm of T cells known as Phospholipase C that in turn modulate T cell antigen receptor signaling. The research team discovered this by treating some T cells with the active form of Vitamin D which resulted in higher expression of the the aforementioned type of enzyme in human skin cells. They also found that naive (to pathogens) T cells did not express the Vitamin D receptor. They also tested this theory by treating T cells with an agonist that blocks the enzyme responsible for converting it into its active form. They found that treating T cells with this agonist did in fact inhibit expression of the Vitamin D receptor and the up regulation of Phospholipase C enzyme. This was further confirmed by isolating T cells from patients with low concentrations of Vitamin D in their blood and comparing them to healthy controls that were not Vitamin D deficient finding that T cells from the former had a lower proliferation index (lower cell division) compared to the latter.

This Science Daily write up below contains a simplified summary of why sufficient Vitamin D levels are needed for T cell stimulation and proliferation.

For T cells to detect and kill foreign pathogens such as clumps of bacteria or viruses, the cells must first be 'triggered' into action and 'transform' from inactive and harmless immune cells into killer cells that are primed to seek out and destroy all traces of a foreign pathogen. The researchers found that the T cells rely on vitamin D in order to activate and they would remain dormant, 'naïve' to the possibility of threat if vitamin D is lacking in the blood.