Figure 1.

Interactions of vitamin D with the gut microbiome and the fetal immune system. Vitamin D up-regulates transforming growth factor β1 and IL-10, which will enhance Treg function and down-regulate CD4 T cells, reducing both Th1 and Th2 CD4⁺ cell inflammation. Vitamin D also enhances antigenic traffic between dendritic cells and Tregs. The gut microbiome is the primary source of antigen for Treg cell processing and may also influence the development of immunity in the fetus. Vitamin D controls the development of gut-associated lymphoid tissue and dendritic cell trafficking from the gut dendritic cells in the gut epithelium to the Tregs. Vitamin D may also control antigenic traffic from the gut microbiome to the gut dendritic cell and the protective organisms in the gut. Modified by permission from Reference 15.