Immunoregulation of Inflammatory and Inhibitory Cytokines by Vitamin D3 in Patients with Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD) is a group of idiopathic, chronic and relapsing inflammatory conditions of the gastrointestinal tract, caused by an aberrant and exaggerated immunological response in the gut. Supplementation of vitamin D3 in patients with IBD exerts both direct and indirect regulatory roles on the naive T cells, thereby maintaining a balance between inflammatory and inhibitory cytokines. The direct actions of vitamin D3 on naive T cells result in the proliferation of more regulatory T cells and inhibitory cytokines such as IL-4, IL-10 and IL-5. The binding of vitamin D to dendritic cells (DCs) through vitamin D receptors inhibits the action of IL-12 on DCs, resulting in the downregulation of Th1 and Th17. On the other hand, this interaction favours Th2 and Treg upregulation and facilitates the maintenance of immune homoeostasis between inflammatory and inhibitory cytokines which is essentially significant in the management of patients with IBD. The aim of this review was to explore the current and mounting scientific evidence on the roles of vitamin D3 in immunoregulation of inflammatory and inhibitory cytokines in patients with IBDs. An extensive literature search was conducted using keywords such as Vitamin D3*, IBD*, inflammatory cytokines*, inhibitory cytokines*, naive-T-cells* and antigen presenting cells* through PubMed, SCOPUS and MEDLINE search engines. The results of the accumulated bodies of research that have been conducted demonstrate that vitamin D3 plays a major role not only in the immunoregulation of cytokines involved in the pathogenesis of IBDs but also in many other inflammatory disorders.