We have previously discussed that one of the mechanisms by which mesenchymal stem cells may have therapeutic activity on multiple sclerosis is through stimulation of T regulatory cells.  In our publication we previously demonstrated that adipose derived cells, which are known to contain mesenchymal stem cells also contain high concentrations of T regulatory cells.

A recent publication (Royal et al. Peripheral blood regulatory T cell measurements correlate with serum vitamin D levels in patients with multiple sclerosis. J Neuroimmunol 2009 Jun 16) assessed circulating levels of 1, 25-dihydroxyvitamin D (1, 25-(OH)2 vitD) and 25-hydroxyvitamin D (25-OH vitD), which are metabolites of vitamin D.  Specifically, 25-OH VitD  (also called calcidiol) is made by chemical modification (hydroxylation) of VitD3 by the liver. Calcidiol made into the active form of vitamin D (calcitriol) by the kidney in a process mediated by the enzyme 25(OH)D-1 alpha hydroxylase. 

So there are two forms of vitamin D: a) Calcidiol and b) Calcitriol. 

The paper demonstrated a positive relationship between high levels of calcitriol and number of T regulatory cells were seen.

The possibility that Vitamin D is related to inhibiting multiple sclerosis comes from some other sources as well.  For example the paper (Correale et al. Immunomodulatory effects of Vitamin D in multiple sclerosis. Brain 2009 May;132(Pt 5):1146-60) makes the following interesting points:

1.  There are reports of diminished multiple sclerosis risk associated with sun exposure and use of Vitamin D supplements.

2.  Circulating levels of vitamin D have been associated with reduced risk.

3.  Out of 60 controls and 132 patients with multiple sclerosis the levels of Vitamin D, both calcitriol and calcidiol were lower as opposed to control.

4.  Patients during relapse had lower vitamin D.

5.  Calcitriol inhibited proliferation of T cells in vitro, stimulated IL-10, and reduced number of cells making IL-17.

6.  T cells can make calcidiol into calcitriol.

7.  Calcitriol increases indoleamine 2,3-dioxygenase activity.

8.  Calcitriol increases Treg cells in vitro.