Immunomodulatory Effect of 1,25-Dihydroxyvitamin D3 in-vitro on Interleukin-10 Secretion by Peripheral Blood Mononuclear Cells in Normal Population

Abstract

Vitamin D has two forms: the inactive form 25(OH) D which is the main circulating form that undergoes hydroxylation in the kidney under the influence of 1α-hydroxylase enzyme to yield the biologically active form 1, 25(OH)2D. Vitamin D plays a primary physiological role in maintaining extracellular calcium ion levels in the human body, primarily by controlling the absorption of calcium from the intestine, through direct effects on bone and also through its effects on PTH secretion. Vitamin D has an important role in both innate and adaptive immune responses as receptors for vitamin D are present in various immune cells, including monocytes, macrophages and dendritic cells, as well as T and B lymphocytes. Vitamin D exerts an inhibitory action on the immune system. In the adaptive immune system, 1, 25(OH)2 D suppresses proliferation of B cells and immunoglobulin production and retards the differentiation of B cell precursors into plasma cells. It also inhibits T cell proliferation, in particular the Th1 cells capable of producing IFN-γ and IL-2. These actions prevent further antigen presentation and recruitment of T lymphocytes (role of IFN-γ), and T lymphocyte proliferation (role of IL-2). In contrast IL-4, IL-5, and IL-10 production can be increased, shifting the balance to a Th2 cell. There are many factors that influence vitamin D levels as age, gender, genetic traits, skin colour, use of sunscreens, clothing practices, season, living condition, outdoor activity, BMI, and administration of some drugs Risk factors for hypovitaminosis D include older age, female sex, winter season, darker skin pigmentation, factors that determine sunlight exposure, such as clothing and cultural practises, and dietary habits. Deficiency of vitamin D, especially in early life, increases the risk of autoimmune diseases like colitis, MS and IDDM. It is also associated with increased risk of infections and cancers. Moreover, higher levels of vitamin D are associated with relative protection against infections, autoimmune diseases and cancers. People with vitamin D deficiency have an impaired ability to react to non-specific inflammatory stimuli as their peripheral blood neutrophils have a decreased random motility, and the phagocytic capacity of neutrophils is impaired.