Медицинская иммунология (Jan 2015)
MECHANISMS OF VITAMIN D ACTION ON THE IMMUNE SYSTEM
Abstract
Besides the well-known effects upon bone metabolism, vitamin D (VD) plays important roles in many other processes in the body, including immune regulation. VD action is carried out through its cellular membrane receptor, which is expressed in a variety of human organs and tissues, e.g., most cells of immune system, as well as epithelial cells lining the mucous membranes. The cell-membrane bound VD receptor is transferred to the cytoplasm, to form a functional complex with vitamin A and its receptor. This complex provides either inhibiting, or enhancing effect upon transcription of hundreds genes in the nuclear DNA, including those that regulate cell growth, differentiation, apoptosis, thus preventing malignancy and angiogenesis. The following effects of VD are supposed with respect to immune system: VD inhibits antigen presentation by dendritic cells, supresses Th1-cell differentiation and the production of Th1-cytokines, shifts the balance of Th1/Th2 cell responses towards the Th2 response, exerts inhibitory effect upon Th17 cells, promotes Treg cell development, and increases their activity. In addition, VD boosts production of «endogenous antibiotics» that may provide powerful effects upon Gram-positive and Gram-negative bacteria, fungi and viruses. Therefore, VD seems quite important for prevention of autoimmune and atopic diseases: multiple sclerosis, rheumatoid arthritis, type 1 diabetes, Crohn’s disease, ulcerative colitis, development of asthma in children and chronic obstructive pulmonary disease. VD protects from a wide range of infections, including tuberculosis, leprosy and respiratory infections, and prevents the development of several tumors. Almost half the population of different countries has a VD hypovitaminosis, often hidden and undiagnosed, and this can be a leading cause of weakened immunity and increased morbidity. The diagnostics of VD hypovitaminosis, prevention and treatment of hypovitaminosis should be among the most important healthcare tasks in Russia.
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