Vitamin D is known for its role in calcium homeostasis and is essential for bone health. It is now known to have other important functions in the body and its deficiency is associated with numerous pathological processes, both infectious and chronic degenerative. Recent studies have shown high prevalences (25 to 90%) of vitamin D insufficiency and deficiencyin sunny countries and locations, affecting all age groups. Allogeneic hematopoietic progenitor cell transplantation (HSCT) is important and potentially curative for hematologic malignancies, were graft-versus-host disease (GvHD) and infections affect outcomes. Vitamin D has emerged as a central player in immunity affecting T and B cells, macrophages and dendritic cells (DCs). A vitamin D-enriched medium maintains an immature DC corpus, associated with decreased ability to stimulate alloreactive T cells. Vitamin D deficiency has been associated with an increased incidence of chronic diseasessuch as graft-versus-host disease (GvHD), supplementation with vitamin D appears to induce an immunotolerance with DCs that has been suggested for the prevention of GvHD. One mechanism for this maintenance of immature DCs has been shown to be the positive regulation of indolamine 2,3-dioxygenase (IDO), an enzyme that transforms tryptophan to quinurenine which is a central feature in DC immunotolerance. Contrary to the suppressive effects on the immune system, vitamin D also has a protective effect against infections. This was from tuberculosis, where traditional treatments withsunlight and cod liver oil, rich in vitamin D, are replaced after the discovery of vitamin D-induced antimicrobial peptides. The two antimicrobial peptides under the influence of Vitamin D are LL-37 (cathelicidin) and β-defensin 2, which have activity against various bacteria, as well as against viruses and fungi.
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2022: 6.012
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