[The early placental trophoblast. I. Normal development and endometrial and non-tumor-induced disorders].

The development of the hemochorial placenta requires, that the trophoblast invades the endometrium, penetrating into its deep layers and blood vessels. Placental tissue includes components from two haplodifferent organisms, the mother and the fetus. Early steps in trophoblastic development are the adhesion and apposition. Invasion is an active process and correlations are observed between cellular invasivness and proteinase production, like uPA, tPA and its inhibitors, for example PAI-1. The process of trophoblast invasion is based on a complex interaction between the trophoblastic cells, various types of matrices and decidual as well as endometrial cells. Immunologic processes, like the production of blocking factors, paraimmune mechanisms and other HLA-dependent processes play an important role. During implantation a differentiation of trophoblastic cells takes place. The syncytiotrophoblast is the active cell of the invasive previllous trophoblast. The intermediate trophoblast plays this role concerning the villous trophoblast. The different trophoblastic cells are characterised by distinct morphologic and immunohistochemical features.