CYTOKERATIN-17 AS AN IMMUNOHISTOCHEMICAL MARKER FOR INTRAMURAL CYTOTROPHOBLAST IN HUMAN FIRST-TRIMESTER UTEROPLACENTAL ARTERIES

Trophoblast cells, as blastocyst-wall derivatives, are of epithelial o rigin and differentiate initially into syncytiotrophoblast and cytotro phoblast subpopulations. Cyto- and syncytiotrophoblasts are the two ce ll types present in the surface cell layers of placental villi. Cytotr ophoblastic cells lie in contact with the basal lamina and are the pro liferating stem cells that guarantee cytotrophoblast and syncytiotroph oblast persistence. Implantation and placenta formation are mainly bas ed on these two cell types. Villous cytotrophoblasts are the stem cell s for all extravillous trophoblast subpopulations, which exhibit stric tly 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 proces s, trophoblast cells, which are located in the remodelled uteroplacent al artery walls, are thus defined as intramural cytotrophoblasts. Trop hoblast differentiation is accompanied and defined by alterations in, for example, the translation pattern for cytokeratin genes. In an immu nohistochemical study, we have demonstrated that only intramural cytot rophoblasts, from all the trophoblast populations of the junctional zo ne, express cytokeratin 17. Furthermore, cell shape and vascular archi tecture indicate that, in human placenta, intra-arterial trophoblast c ells reach their destination by migration through the endometrial inte rstitium with consecutive intravasation. Cytokeratin 17, in particular , can therefore be used as a specific immunohistochemical marker for t he intramural trophoblast subpopulation.