Fig. 2.

Schematic representation of the anatomical, physiological, and immunological placental barriers designed to limit microbial invasion. Three main types of cells on the fetal side of the placenta prevent access of bacterial invaders to the fetal circulation: the syncytiotrophoblast, the cytotrophoblasts, and the extravillous trophoblasts (EVT). The basement membrane also serves as a physical barrier that averts bacterial invasion. Additionally, maternal immune cells and immunoglobulins (not depicted) are near the EVTs to aid in the defense against microbial insults