Effect of vitamin D₃ supplementation on peripheral B cell differentiation and isotype switching in patients with multiple sclerosis

Background: Vitamin D has been proposed as a promoter of immune homeostasis in multiple sclerosis (MS). During the past decade, the focus of the effects of vitamin D has been on dendritic cells and on T cells. Since there is an increasing interest in the role of B cells in the pathophysiology of MS, we studied the role of vitamin D on B cells in vivo in patients with MS. Objective: We explored the effects of 12 weeks high-dose vitamin D3 supplementation on peripheral B cell differentiation, immunoglobulin production and levels of B cell activating factor (BAFF) in 15 patients with MS. Methods: Circulating B cell subsets were characterized by flow cytometry. Plasma immunoglobulin levels were assessed by nephelometry. Plasma BAFF levels were assessed by enzyme-linked immunosorbent assay (ELISA). Results: Although a significant increase serum 25-hydroxyvitamin D was induced, we found no significant shift in B cell differentiation, isotype switching, or plasma BAFF levels. Conclusion: In patients with MS, supplementation of high doses vitamin D3 does not have substantial effects on phenotypic markers of B cell differentiation in circulating B cells. Future studies may unravel more subtle changes in the B cell compartment, either in the circulation or in the central nervous system.