Figure 3.

Regulation of immune function by 1,25(OH)₂D. 1,25(OH)₂D suppresses adaptive immunity (A) by inhibiting the maturation of dendritic cells, reducing their capacity to present antigen to CD4 cells. 1,25(OH)₂D further inhibits the proliferation and differentiation of CD4 cells into Th1 and Th17 cells and promotes the production of Th2 and Treg cells. On the other hand 1,25(OH)₂D promotes innate immunity (B) in that when the macrophage is activated by TLRs, VDR and CYP27B1 are induced enabling the macrophage to produce 1,25(OH)₂D, which then induces cathelicidin, a potent antimicrobial peptide.