Figure 4.

Implication of the placental microbiome in pre-eclampsia. Alteration of placental structures could result from the direct action of pathogenic bacteria through the release of lipopolysaccharide (LPS) or lipoproteins (LPP), which activates inflammatory cytokines via interactions with toll-like receptors (TLRs especially TLR4/TLR2). This invokes the pathogenic process of pre-eclampsia. Whereas, under physiological condition commensal bacteria release bacterial products such as LPS/LPP from gram-negative and positive bacteria, respectively, which is ligated by toll-like receptors (TLR4) and activated by TLR2 located on the surface of trophoblast. This in turns activates regulatory cytokines to promote tolerogenic microenvironment (maternal-fetal immune tolerance) and maintains energy homeostasis in normal pregnancy. SA, spiral artery.