Fig 1.

Vitamin D metabolism and innate immune signaling in the monocyte/macrophage. Schematic representation illustrating the regulation of expression of genes that encode antimicrobial peptides, pattern recognition receptors, and cytokines/chemokines by the 1,25D‐bound vitamin D receptor (VDR). In response to 1,25D, the VDR induces expression of the pattern recognition receptor NOD2, antimicrobial peptides CAMP and HBD2/DEFB4, and cytokines IL‐1β and IL‐8. The 1,25D‐VDR complex also functions to suppress HAMP expression, leading to increased ferroportin‐mediated export of iron. Upon stimulation with the ligand muramyl dipeptide (MDP) generated by the breakdown of bacterial peptidoglycan, NOD2 and IL‐1β can enhance HBD2, CAMP, and IL1B expression.