Peripheral blood regulatory T cell measurements correlate with serum vitamin D levels in patients with multiple sclerosis

Abstract

Vitamin D has been associated with a decreased risk of multiple sclerosis (MS). In this study, serum 1, 25-dihydroxyvitamin D (1, 25-(OH)2 vitD) and 25-hydroxyvitamin D (25-OH vitD), regulatory T cell percentages and naïve and memory T helper cell subsets were measured in 26 patients with multiple sclerosis, 21 who were not on treatment with disease modifying therapy. These studies showed an inverse correlation between 25-OH vitD levels and Treg cell percentages and a direct correlation between Treg cell percentages and 1, 25-(OH)2 vitD:25-OH vitD ratios. In addition, 25-OH vitD levels correlated directly and 1, 25-(OH)2 vitD:25-OH vitD ratios correlated inversely with CXCR3+ naïve T helper cell percentages and CXCR3+naïve:CXCR3+ memory T helper cell ratios. All together, these data demonstrate that vitamin D measurements can reflect measures of immune status among patients with MS.

Introduction

In recent years, epidemiological studies have demonstrated an association between vitamin D supplementation and lower risk of MS (Munger et al., 2004, Munger et al., 2006) and that individuals with lower vitamin D levels have a higher risk of the disease(Munger et al., 2006). In studies involving animals with experimental allergic encephalomyelitis (EAE), vitamin D has been demonstrated to suppress proinflammatory cytokine production and to increase secretion of anti-inflammatory cytokines(Cantorna et al., 1996, Racke et al., 1995). These effects occurred in association with decreased T cell expression of interferon (IFN)-γ and tumor necrosis factor (TNF)-α, suppression of monocyte production of interleukin (IL)-12, and increased expression with IL-4 (Cantorna et al., 1996, Cantorna et al., 1999, Cantorna et al., 2000, Garcion et al., 2003, Hayes et al., 1997, Hayes, 2000, Mattner et al., 2000, Meehan and Deluca, 2002). The immune modulatory properties of vitamin D are mediated in part through effects on regulatory T (Treg) cells (Adorini, 2003, Cantorna et al., 1994, Gregori et al., 2001, Spach et al., 2006). Treg cells, which have been demonstrated to suppress the development and progression of autoimmune demyelination in EAE (Kohm et al., 2002), develop in the thymus in mice from naïve (CD45RA+) T helper cells (Sakaguchi et al., 2003). Treg cells can be also induced in the periphery from T cells following antigen presentation by dendritic cells rendered tolerogenic as a result of exposure to vitamin D (Adorini, 2003). Treg cells are CD4+ T cells that express CD25, the alpha chain of the IL-2 receptor, and high levels of the transcription factor forkhead box P3 (FoxP3). The suppressive activity of Treg cells can be demonstrated in vitro by the ability of these cells to suppress the proliferation of responder, i.e., non-Treg cell, targets, with such suppression being mediated by CD4+CD25+FoxP3^high cells(Makita et al., 2004, Sugiyama et al., 2005).

The major form of vitamin D in circulation in humans is 25-hydroxy vitamin D (25-OH vitD), which is synthesized subsequent to conversion of 7-dehydrocholesterol to previtamin D3 which then undergoes temperature dependent isomerization to vitamin D3 (VD3; cholecalciferol) (Brown et al., 1999). VD3 is converted to 25-OH vitD primarily in liver by the enzyme 25 hydroxylase. This enzyme is also produced by cells in extrahepatic tissues such as the intestine, kidney and skin as well as by neurons, activated macrophages, and microglial cells, and T cells (Brown et al., 1999, Holick, 2004). The metabolically active form of vitamin D, 1, 25 dihydroxyvitamin D (1, 25-(OH)2 vitD) is produced in the kidney and is subsequently bound by the vitamin D receptor, which then forms a heterodimer with the retinoid X receptor (RXR), a vitamin A receptor. These ligand-receptor interactions result in the formation of a transcriptional complex that activates specific genes in cells (Brown et al., 1999, Deluca and Zierold, 1998). Though previous studies have documented the in vitro effects of vitamin D on Treg cell production, none to date have examined possible links between this micronutrient and Treg cell levels in vivo. Therefore, in these studies were examined associations between vitamins D and Treg cell measurements in patients with MS. These studies show a direct correlation between percentages of CD4+CD25+FoxP3^high Treg cells and ratios of vitD:25-OH vitD levels and an inverse correlation with 25-OH vitD measurements. Also observed were correlations with CXCR3+ naïve (CD45RA+) T helper cells, which can potentially traffic across the blood–brain barrier in response to proinflammatory stimuli, which were opposite those observed for Treg cells percentages. These findings are consistent with previous observations that support the importance of vitamins D in suppressing disease activity in MS.