The Distribution of Caveolin-1 in Human Term Placenta and the Derivation of the Endothelial Cells Lining its Basal Plate

The initial aim of this research was to establish the distribution of the protein caveolin-1 in the human term placenta, using an indirect immunofluorescence technique. The findings of this survey showed that caveolin-1 was expressed in all the predicted places (vascular endothelium, smooth muscle and fibroblasts), but also by cells lining the basal plate. These cells were investigated further, firstly by transmission and scanning electron microscopy, then by immuno-gold electron microscopy. The findings of the immuno-gold study suggested a vectorial nature of caveolae trafficking in both foetal endothelial cells and in the endothelial-like cells lining the basal plate. This study also showed that some leucocytes express caveolin-1. The cells lining the maternal blood space above the basal plate of the placenta had been thought to be trophoblastic (foetal) but the initial results obtained using immunofluorescence indicated that the lining consisted rather of a mosaic of two types of cells. Some of these were trophoblastic but others were seen to be more similar to endothelial cells. To determine whether these latter cells were of maternal derivation, placentae from neonates of known gender were used in a cytogenetic analysis, to establish their provenance unequivocally. The probe used in these in situ hybridisation experiments was complementary to a portion of the human Y-chromosome (only found in males). Cells to which this probe hybridised must therefore be male; a failure to hybridise meant that they must be maternal. Some cells resident in the basal plate were shown to have more than one Y-chromosome in a single interphase nucleus and were taken to be polyploid trophoblast ‘giant’ cells. Further collaborative experiments showed that the area fraction occupied by the lining endothelial cells was greater in pre-eclamptic placentae than in placentae from normotensive births; the significance of this in the aetiopathology of this disease is discussed. Cells that play a key role at the maternal-foetal interface have been carefully characterised in this study and have been shown to form a continuous endothelial/epithelial layer of both maternal and foetal origin.