Listeria monocytogenes produces severe fetoplacental infections in humans. How it targets and crosses the maternofetal barrier is unknown. We used immunohistochemistry to examine the location of L. monocytogenes in placental and amniotic tissue samples obtained from women with fetoplacental listeriosis. The results raised the possibility that L. monocytogenes crosses the maternofetal barrier through the villous syncytiotrophoblast, with secondary infection occurring via the amniotic epithelium. Because epidemiological studies indicate that the bacterial surface protein, internalin (InlA), may play a role in human fetoplacental listeriosis, we investigated the cellular patterns of expression of its host receptor, E-cadherin, at the maternofetal interface. E-cadherin was found on the basal and apical plasma membranes of syncytiotrophoblasts and in villous cytotrophoblasts. Established trophoblastic cell lines, primary trophoblast cultures, and placental villous explants were each exposed to isogenic InlA؉ or InlA؊ strains of L. monocytogenes, and to L. innocua expressing or not InlA. Quantitative assays of cellular invasion demonstrated that bacterial entry into syncytiotrophoblasts occurs via the apical membrane in an InlA-E-cadherin dependent manner. In human placental villous explants, bacterial invasion of the syncytiotrophoblast barrier and underlying villous tissue and subsequent replication produces histopathological lesions that mimic those seen in placentas of women with listeriosis. Thus, the InlA-E-cadherin interaction that plays a key role in the crossing of the intestinal barrier in humans is also exploited by L. monocytogenes to target and cross the placental barrier. Such a ligand-receptor interaction allowing a pathogen to specifically cross the placental villous trophoblast barrier has not been reported previously.

Prostanoids influence differentiation in diverse cell types. Altered expression of cyclooxygenase and prostaglandins has been implicated in the pathophysiology of placental dysfunction, which results in preeclampsia and fetal growth restriction. We hypothesized that prostanoids modulate differentiation and apoptosis in cultured human trophoblasts. Villous cytotrophoblasts were isolated from term human placentas and cultured in serumfree medium. The level of human chorionic gonadotropin was used as a marker of biochemical differentiation of primary trophoblasts, and syncytia formation was used as a marker of morphologic differentiation. Of the prostanoids tested, we found exposure to thromboxane A 2 hindered both biochemical and morphologic differentiation of cultured trophoblasts. As expected, human chorionic gonadotropin levels in the media were elevated in a concentration-dependent manner in the presence of the thromboxane synthase inhibitor, sodium furegrelate, or the thromboxane A 2 receptor blocker SQ 29,548. Furthermore, thromboxane A 2 enhanced trophoblast apoptosis, determined using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, cell morphology, and a concentrationdependent increase in p53 expression. We conclude that thromboxane A 2 hinders differentiation and enhances apoptosis in cultured trophoblasts from term human placenta. We speculate that thromboxane may contribute to placental dysfunction by restricting differentiation and enhancing apoptosis in human trophoblasts. The function of the human placenta depends on multinucleated, terminally differentiated syncytiotrophoblasts. This epithelium is in direct contact with maternal blood and regulates maternal-fetal exchange of micronutrients and gases. The syncytiotrophoblast arises from fusion of relatively undifferentiated, mitotically active cytotrophoblasts. This process involves morphologic and biochemical differentiation. Morphologic differentiation is defined by fusion of mononucleated cytotrophoblasts with adjacent syncytium (1). Biochemical differentiation is characterized by production of hormones such as hCG and human placental lactogen (2-4). Preeclampsia and FGR are associated with trophoblast hypoxia and placental dysfunction (5). Villi from women with these conditions typically exhibit diminished villus formation, prominent cytotrophoblasts, enhanced syncytial knot formation, and apoptosis (6, 7). An increase in TX synthesis has been demonstrated in villi (8, 9) and trophoblasts (10, 11) from preeclamptic women compared with healthy control subjects. Importantly, FGR (12) and preeclampsia (13) are associated with elevated TXA 2 levels in the circulation of pregnant women. Although the effect of prostanoids on vascular reactivity is well known (14), recent studies indicate that prostanoids also regulate proliferation, differentiation, and apoptosis in many cell types (15-18). We tested the hypothesis that prostanoids influence the differentiation of cultured trophoblasts from term human placenta. We found ...