Syncytial trophoblasts

However, only the extracellular domains immediately adjacent to the cell membrane and the (32 microglobulin peptide have clear homology with the immunoglobulin domains. The al and ct2 segments of class I and the al and (31 domains in class II have quite an unusual structure. Class I molecules are present on virtually every cell in the body, the most notable exception being the syncytial trophoblast of the placenta. Class II expression is far more restricted B cells, dendritic cells which present antigen to T cells, and macrophage express abundant class II molecule on their surfaces. However, most other tissues can be induced to express class II molecules under the influence of soluble mediators such as 7-interferon. 

Wislocki and Bennett (1943) reported that yellow phenylhydrazones could be produced in the syncytial trophoblast of placental villi of primates, a zone characterized by numerous small lipid droplets. Bire-fringent crystals were located in the same layer. They implied that the syncytium was thus the presumptive source of the steroid hormones produced by the placenta. 

Xu et al. [76] have showed that human embryonic stem cells by treatment with bone morphogenetic protein-4 can be driven to differentiate into tro-phoblasts which have the ability to syncytialize and form confluent mono-layers. The differentiated cells express a number of trophoblast markers and secrete placental hormones and thus may provide an alternative placental model. Under the culture conditions used, however, the cells propagated poorly. 

It needs to be mentioned here that there remains some controversy over the placental expression of P-gp as a function of gestational age. An immunohis-tochemical study done by Macfarland et al. showed that P-gp was localized to the microvillous border of trophoblasts in first trimester placenta, but not in term placenta [85], Subsequent studies refuted this to show that MDR1 mRNA is present throughout pregnancy [94], More recently, enzyme-linked immunosorbent assay (ELISA) performed in syncytial microvillous membrane showed that P-gp protein expression in early gestational age placenta is about... 

The blastocyst implants into the maternal endometrial wall on about the 7th day of embryonic life. Trophoblastic cells attach to the uterine mucosa by apposition and adhesion. Under the influence of progesterone and estrogen, the uterine lumen closes, which brings the blastocyst into close contact with the endometrium. Adhesion of the trophoblastto the uterine epithelium occurs with increasing apposition and involves cell surface glycoproteins. The uterine epithelium is penetrated by syncytial growths on the trophoblast into the adjacent uterine epithelial cells. Subsequently, the trophoblastic membranes... 

The placental barrier in rats can be disturbed by fetal hypertension that opens paracellular pathways through the syncytial layer of the trophoblast (Kertschanska, Stulcova et al. 2000). On the other hand, Hua and eoworkers (Hua, Zhu et al. 2009) showed that contrast-enhanced ultrasound does not increase the permeability of placenta to macromolecules larger than lanthanum or albumine. 

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