VDR and immune system disorder: Establishment of the complex between VDR and its ligand, the active form of vitamin D, i.e. vitamin D 1,25(OH)2D3, leads to the translocation of the activated VDR from the cytoplasm into the nucleus and hence to the direct regulation of expression of hundreds of genes, including those involved in infection response and immune disorders [38], through the binding of VDR to the promoters and regulatory elements of those genes.