VDR and infection: These receptors initiate a signaling cascade that induces upregulation of the VDR and CYP27B1, which leads to the conversion of 25(OH)D to 1,25(OH)2D. Binding of 1,25(OH)2D to the VDR leads to the expression of multitarget genes, which modulate the function of monocytes/macrophages during infection (see Figure 2B).