Figure 2.

Schematic showing distribution of immune cells across materno–fetal interface during early pregnancy. Macrophages, Treg cells, and dendritic cells are present in the myometrium as well as decidua, while uterine natural killer (uNK) cells are restricted to decidua. The effective crosstalk between various immune cells and extravillous trophoblast cells creates an immunosuppressive environment and helps in the formation of various pregnancy-related tissues, both of which are essential for a successful pregnancy. Extravillous cytotrophoblasts enter the decidua to reach out to maternal spiral arteries for obtaining required nutrient to support developing embryo. Other nutrients, gas, and waste exchange happens via placental villus, which interacts with the maternal blood directly. The villus has double layer of cells consisting of syncytiotrophoblasts and cytotrophoblasts. It encloses the fetal blood vessels along with fibroblasts and fetal macrophages (Hofbauer cells). Immune cells as well as placental cells protect the fetus by expressing PRRs, such as Toll-like receptors, on their surface throughout the pregnancy.