Abstract
Studies over the last two decades have revealed profound immunomodulatory aspects of vitamin D on various aspects of the immune system. This review will provide an overview of Vitamin D metabolism, a description of dendritic cell subsets, and highlight recent advances on the effects of vitamin D on dendritic cell function, maturation, cytokine production and antigen presentation. The active form of vitamin D, 1,25(OH)2D3, has important immunoregulatory and anti-inflammatory effects. Specifically, the 1,25(OH)2D3-Vitamin D3 complex can affect the maturation and migration of many dendritic cell subsets, conferring a special immunoregulatory role as well as tolerogenic properties affecting cytokine and chemokine production. Furthermore, there have been many recent studies demonstrating the effects of Vitamin D on allergic disease and autoimmunity. A clear understanding of the effects of the various forms of Vitamin D will provide new opportunities to improve human health.
Highlights
Studies over the last two decades have revealed profound immunomodulatory aspects of vitamin D on various aspects of the immune system
dendritic cells (DCs) are replenished from bone marrow (BM) precursors, but may arise from blood monocytes under inflammatory conditions [27]
The modifications in phenotype as well as the functional plasticity of DCs varies through multiple signal codes that are generated by different stimuli in humans [66]
Summary
Vitamin D plays a key role in maintaining mineral homeostasis. over the last several years, non-classic actions of vitamin D have been described. 1,25(OH) D3 strongly induces gene expression of CYP24A1 to produce the enzyme 25-Hydroxyvitamin D3 -24-hydroxylase that initiates catabolic degradation, resulting in the formation of 1,24,25(OH) vitamin D3 and in the formation of 1α-hydroxy-23-carboxy-24,25,26,27-tetranorvitamin D3 [9] This enzyme promotes the formation of 24,25(OH) vitamin D3 via negative feedback by decreasing the 25(OH)D substrate available for 1α hydroxylation [9,10]. 1,25(OH) D3 has different functions including regulation of intestinal calcium and phosphate absorption, calcium mobilization from bone, and reabsorption of calcium in the kidney. It has different immune effects in the body [1,11]. Given the evidence that VDR is expressed in many immune cells, including monocytes/macrophages, B and T cells [10,23,24,25,26] as well as DCs, along with the ability of DCs to produce 1,25(OH) D3 [25], this review will focus on the function of VDR in dendritic cells
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