Characterization of first trimester human fetal placental vessels using immunocytochemical markers

Cell differentiation markers on placental villi from the first trimester of human pregnancy have been studied by indirect immunofluorescence. Fluorescence labelling with antibodies against CD34 and CD31 was conspicuous in the vascular cells. The vascular paracellular clefts were labelled by anti-cadherin-5. A few vascular cells exhibited a positive reaction for von Willebrand factor, high-molecular-weight melanoma-associated-antibody and alpha-sm-actin compared to term pregnancy, indicating changes in protein expression during vascular differentiation. The poor anti-collagen IV reaction and the absence of a sm-myosin fluorescent signal observed around the vessels confirned the immaturity of the vessels. In contrast, strong reactions have previously been obtained with the latter antibodies in similar locations using term placental villi. A labelling was observed for antibodies against alpha3 and alpha5 integrins in these immature placental vessels suggesting cell-matrix interactions with specific domains of laminin or fibronectin. The vascular cells were also stained by anti-CD26. Surprisingly, the fetal vascular cells exhibited immunostainings in common with the villous cytotrophoblast (CD26) or the syncytiotrophoblast (cadherin-5) and cell islands cytotrophoblast (CD31, cadherin-5, alpha3 and alpha5 integrin subunits). These observations suggested a two step process for fetal vasculogenesis in the villi: i/ the formation of peripheral vessels induced by growth factors or cytokines derived from the nearby trophoblast, ii/ the development of muscular vessels due to growth factors or cytokines production induced by circulatory changes.