Die Basalplatte der reifen menschlichen Placenta

The fibrinoids of the human placenta: origin, composition and functional relevance

Placental fibrinoids are extracellularly deposited materials which are histologically glossy and acid staining, and can be found in every normal and pathological placenta at all stages of pregnancy. The amount of fibrinoid is, in general, independent of pregnancy outcome and fetal wellbeing. According to new findings, the classical histological term "fibrinoid" covers two distinctive extracellular matrices which differ as regards structure, composition and function. Fibrin-type fibrinoid is mostly composed of fibrin together with other molecules derived from blood clotting or degenerative processes. It is mainly a maternal blood-clot product which is used (a) to adapt the intervillous space to optimized flow conditions and (b) to control growth of the villous trees by encasing new villous branches which caused intervillous stasis or turbulence of maternal blood. Moreover, fibrin-type fibrinoid replaces degenerative syncytiotrophoblast at the maternofetal exchange surfaces, thus acting as a kind of substitute barrier. Matrix-type fibrinoid is a secretory product of invasive extravillous trophoblast cells. It shares some similarities with basement membranes, however, it is secreted in an apolar fashion, embedding the secreting cells. Like basement membranes, it contains laminins, collagen IV, and heparan sulfate. In addition, oncofetal fibronectins, vitronectin, and i-glycosylated molecules but no collagens I, III, and VII can be found. Matrix-type fibrinoid is thought to regulate trophoblast invasion by specific interactions with cell surface integrins. As a kind of "glue", it anchors the placenta to the uterine wall and seems to play an important role in materno-fetal immune interactions at this particular site. Both types of fibrinoid are usually co-localized, thus indicating close morphogenetic and functional interrelations.

Immunohistochemical evidence for the heterogeneity of maternal and fetal vascular endothelial cells in human full-term placenta

The heterogeneity of endothelial cell surface antigen expression was studied in 5 human full-term placentae by means of indirect immunohistochemistry using 9 monoclonal antibodies and by staining with fluorescent-conjugated Ulex europaeus lectin, both of which are widely used endothelial cell markers. (1) A highly specific, homogeneous staining of fetal and maternal placental vessels of all sizes and anatomical regions was observed by the monoclonal antibodies PAL-E, QBEND10 and 1F10. These antibodies were even more specific than Ulex europaeus lectin, factor VIII antibody and von Willebrand factor antibody, which cross-reacted with some non-endothelial cells and structures. The reactivity of PAL-E, QBEND10 and 1F10 with residual surface cells of the basal plate strongly suggests an endothelial origin of these cells. (2) In contrast to other organs, PAL-E, QBEND10 and HM15/3 strongly stained endothelial cells of the macrovascular system in the human placenta. This might indicate an organ-associated heterogeneity of fetal endothelial cells. (3) Monoclonal antibodies against receptors for transferrin and IgG (Fc gamma RII) labeled the endothelial cells of fetal placental vessels with increasing intensity distal to the insertion of the umbilical cord. The vessels of the umbilical cord itself were unreactive. This might suggest a heterogeneity of macro- and microvascular endothelial cells.

[Lightmicroscopical and histochemical studies on the chorionic plate of the mature human placenta (author's transl)]

The chorionic plate of the normal mature human placenta was studied by light-microscopy and enzyme-histochemistry. Thereby the following findings were obtained in the various layers: The enzyme content of the amniotic epithelium refers to a secretory activity. The question with regard to a resorbant activity remains unclarified. The cells of the amnion mesoderm chiefly show the enzymes of the intermediary metabolism. The intermediate layer consists of mesothelium cells which furthermore have also phagocytotic activity. The chorionic plate mesoderm consists of several layers with connective tissue cells of diverse stage of differentiation. In the early embryonic phase they differentiate amnionward from the primary cytotrophoblast layer and still get cellular supply from residual primary cytotrophoblastic cells up to the date of birth. The enzymes of the primary cytotrophoblast cells refer accordingly with a strong activity of G6PDH to proliferation and differentiation. One part of the X-cells embedded in the Langhans fibrinoid stria descends from this primary cytotrophoblast layer; but in part they differentiate also from the Langhans cells of the placental villi surrounded by the fibrinoid stria. According to their different descent, these cells show a varying content of enzymes. The bordering of the chorionic plate to the intervillous space is represented by a rudimentary, syncytotrophoblast layer.

[Decidualisation of the endometrial stromal cell. An electron microscopic study (author's transl)]

The fine structural changes of the endometrial stromal cell from late secretory phase up to full developed decidua cell have been investigated by means of electron microscope. During decidual transformation the cell volume, the assortment of cytoplasmic organelles and the mode of intercellular attachments undergo characteristic alterations. These alterations reflect an adaptation on new cellular functions. In contrast to the structural organization, which is transformed continuosly, the encymatic cell pattern exerts a step wise gradual transformation, since new encymatic capacities can only arise after their funtional structures have been established. To the most important functions of decidua cells and their prestages belong secretory and endocrine activities. Precollagen fibrills represent a specific secretory product of the stroma reticulum cells. The active involvement of the full differentiated decidua cells in steroid metabolism is indicated by characteristic transformation of the cytoplasmic organization concomittantly to the appearance of intracellular steroid dehydrogenase activities. So-called karyosoma could be demonstrated within the nuclei of postovulatory stromal reticulum cells as in decidua cells. Similar nuclear differentiations have been observed in various target cells of steroid hormones. They possibly are structural manifestations of the hormonal interaction with the nuclear DNA.

[Light and electron microscopic investigations on the chorionic plate of the human placenta at term (author's transl)]

The chorionic plate of the human placenta at term consists of amniotic epithelium, amniotic connective tissue, intermediate layer, chorionic connective tissue, cytotrophoblast, and syncytiotrophoblast. - The connective tissue layers are divided into unorientated (situated just below the amniotic epithelium and in direct contact with the trophoblast) and orientated layers (between the two unorientated connective tissue layers). Besides an accelular border below the amniotic epithelium the connective tissue includes fibrocytes, fibroblasts, histiocytes, and old Hofbauer cells in the intermediate layer. - From the edge of the chorionic plate to its centre, the number of well preserved cytotrophoblasts decreases; instead of them especially intercellular substances (subchorial fibrinoid) but also degenerating cells predominate. In the trophoblast layer rests of chorionic villi are localized. Among the intact cytotrophoblasts 4 types can be distinguished (less differentiated, well differentiated, spongiotrophoblast-like, and glycogen-rich cytotrophoblastic cells). They are interpreted as different developmental stages of one and the same cell population. - The syncytiotrophoblast is inter rupted at many places; only fragments can be observed. Then cytotrophoblastic cells or intercellular substances may form the border to the intervillous space.