Peripheral Immunological Effects of High-dose Vitamin D Treatment in Healthy Subjects

Vitamin D deficiency is associated with the risk of developing MS. Vitamin D treatment has therefore been tested as a background treatment for this pathology, with a seemingly modest clinical effect. Indeed, the first therapeutic trials using high doses of vitamin D (SOLAR and CHOLINE) did not show a significant effect on short-term relapses. However, these two studies showed a significant decrease in the radiological activity of MS on MRI, suggesting a significant immunomodulatory efficacy but a weak clinical benefit in the short term. Vitamin D has a pleiotropic effect on the immune system inducing overall immunomodulation through transcriptomic modulations, under the control of many individual genetic factors. However, in vivo, only one therapeutic trial has compared the immunological effect of Vitamin D in healthy subjects and in patients with a first demyelinating episode. Analysis of PBMC by flow cytometric cell sorting based on a very small number of markers (CD3, CD8, IL-17, IFN-g) did not find any significant quantitative modulation of Th17 or of their production of IL-10, IL-17 and IFN-g after treatment with Vitamin D measured by ELISA. However, the evolution of anti-inflammatory lymphocyte populations has not been evaluated. A few in vitro studies suggest that the effect of vitamin D may be incomplete on the lymphocytes of MS patients. The study investigators will use an immunological FACS approach to describe activation markers and measure the intensity of changes induced in healthy subjects after 3 months of high-dose cholecalciferol versus placebo treatment using the same protocol as the D-Lay MS (NCT01817166) study.