Cytokeratin 17 as an immunohistochemical marker for intramural cytotrophoblast in human first trimester uteroplacental arteries.
Trophoblast cells, as blastocyst-wall derivatives, are of epithelial origin and differentiate initially into syncytiotrophoblast and cytotrophoblast subpopulations. Cyto- and syncytiotrophoblasts are the two cell types present in the surface cell layers of placental villi. Cytotrophoblastic cells lie in contact with the basal lamina and are the proliferating stem cells that guarantee cytotrophoblast and syncytiotrophoblast persistence. Implantation and placenta formation are mainly based on these two cell types. Villous cytotrophoblasts are the stem cells for all extravillous trophoblast subpopulations, which exhibit strictly regulated invasiveness. One aspect of extravillous trophoblasts is that they invade maternal endometrial spiral arteries and dilate them in order to achieve sufficient fetal blood supply. During this process, trophoblast cells, which are located in the remodelled uteroplacental artery walls, are thus defined as intramural cytotrophoblasts. Trophoblast differentiation is accompanied and defined by alterations in, for example, the translation pattern for cytokeratin genes. In an immunohistochemical study, we have demonstrated that only intramural cytotrophoblasts, from all the trophoblast populations of the junctional zone, express cytokeratin 17. Furthermore, cell shape and vascular architecture indicate that, in human placenta, intra-arterial trophoblast cells reach their destination by migration through the endometrial interstitium with consecutive intravasation. Cytokeratin 17, in particular, can therefore be used as a specific immunohistochemical marker for the intramural trophoblast subpopulation.