Role of Active Vitamin D3 in Immunity

Abstract

precursor 25 hydroxy cholecalciferol. Only recently, its crucial role as a potential immune modulator has been recognized. Clear identification of its well-documented roles in immune response and autoimmunity has led it to being actively pursued as a potential therapeutic agent. 1,2 Vitamin D3 influences all the key cells of the immune system and produces intracrine and paracrine effects on them. Most immune cells have the enzyme system to produce the active form of vitamin D3. It is an inhibitor of differentiation and maturation of dendritic cells (DCs) and decreases their antigen-presenting activity. It acts directly on T cells and alters the profile of their proliferation and differentiation. It promotes anti-inflammatory environment by inhibiting the Th1 and Th17 cells and promoting the Th 2 and T reg cell differentiations. Vitamin D3 induces antimicrobial effects in monocytes/macrophages by enhancing their phagocyte activity as well as helping the synthesis of antimicrobial peptides. Sunlight-mediated epidermal expression of 1,25(OH) 2 D3 acts as the link between the environment and immune system. It induces suppression of cutaneous immune response through the T-regulatory cells. Overall, it is considered an important regulator of both innate and adaptive immune systems. There is an emerging view that the vitamin D deficiency, which is widely prevalent these days, could have an important role in immune disorders, especially the autoimmune diseases. 2In this review, we present an overview of the current knowledge on vitamin D as an immunomodulator with the underlying molecular mechanisms and its possible role in immunological response with future implications. VITAMIN D-THE MOLECULEErgocalciferol, vitamin D2, and cholecalciferol, vitamin D3, are the two major forms of vitamin D. Vitamin D2 is synthesized by plants and fungi, while vitamin D3 is produced in large quantities in humans by photosynthesis in the skin. The ultraviolet (UV) light falling on the skin catalyzes the conversion of 7-dehydro-cholesterol into the previtamin D, which then spontaneously ABSTRACT Introduction:The active vitamin D3-1,25 dihydroxy cholecalciferol-is the key player in calcium and phosphorus metabolism and skeletal growth and functions. However, recent new developments have revealed its role in other tissues as well, referred to as the nonclassical actions of vitamin D. Not only the endocrinal effects, evidence indicates that vitamin D3 also has autocrine and paracrine functions due to its extrarenal synthesis by many cells, including the immune cells. All cells of the immune system have vitamin D receptors and show wide-ranging effects to it. It impacts both the innate and adaptive immune systems and the overall influence points to anti-infective, anti-inflammatory, immunosuppressive, and regulatory roles. It shows a significant role in chronic inflammatory and autoimmune diseases as well in susceptibility to infections.In this review, newer developments on the role of vitamin D in immunity and the underlying mechanism are d...