title: Vitamin D: modulator of the immune system.
abstract: 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the active form of vitamin D, is known to regulate calcium and phosphorus metabolism, thus being a key-player in bone-formation. However 1,25(OH)(2)D(3) also has a physiological role beyond its well-known role in skeletal homeostasis. Here, we describe 1,25(OH)(2)D(3) as an immunomodulator targeting various immune cells, including monocytes, macrophages, dendritic cells (DCs), as well as T-lymphocytes and B-lymphocytes, hence modulating both innate and adaptive immune responses. Besides being targets, immune cells express vitamin D-activating enzymes, allowing local conversion of inactive vitamin D into 1,25(OH)(2)D(3) within the immune system. Taken together, these data indicate that 1,25(OH)(2)D(3) plays a role in maintenance of immune homeostasis. Several epidemiological studies have linked inadequate vitamin D levels to a higher susceptibility of immune-mediated disorders, including chronic infections and autoimmune diseases. This review will discuss the complex immune-regulatory effects of 1,25(OH)(2)D(3) on immune cells as well as its role in infectious and autoimmune diseases, more in particular in tuberculosis and type 1 diabetes (T1D).
authors.affiliation: Laboratory of Experimental Medicine and Endocrinology (LEGENDO), Katholieke Universiteit Leuven. 3000 Leuven, Belgium.
authors.forename: Femke
authors.initials: F
authors.lastname: Baeke
authors.forename: Tatiana
authors.initials: T
authors.lastname: Takiishi
authors.forename: Hannelie
authors.initials: H
authors.lastname: Korf
authors.forename: Conny
authors.initials: C
authors.lastname: Gysemans
authors.forename: Chantal
authors.initials: C
authors.lastname: Mathieu
mesh_terms: D056704:Adaptive Immunity / Q000502:physiology; D001327:Autoimmune Diseases / Q000276:immunology; D002117:Calcitriol / Q000172:deficiency / Q000502:physiology* / Q000627:therapeutic use; D003141:Communicable Diseases / Q000276:immunology; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology / Q000517:prevention & control; D006801:Humans; D007107:Immune System / Q000502:physiology*; D007113:Immunity, Innate / Q000502:physiology; D018167:Receptors, Calcitriol / Q000819:agonists; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology; D014397:Tuberculosis, Pulmonary / Q000188:drug therapy / Q000276:immunology; D014815:Vitamins / Q000502:physiology* / Q000627:therapeutic use
chemical_list: D018167:Receptors, Calcitriol; D014815:Vitamins; D002117:Calcitriol