Comparative Analysis of Trophoblasts and Angiogenesis in Human Placental Compartments

SUMMARY: Trophoblasts perform different functions depending on their location. This study aimed to obtain structural clues about the functions of villous and extravillous trophoblasts by using light and electron microscopy. Term placenta samples were obtained from 10 healthy pregnant women following cesarean sections. Frozen sections were stained with hematoxylin-eosin, semi- thin sections were stained with toluidine blue and examined with a light microscope, while thin sections were contrasted using uranyl acetate-lead citrate and evaluated under an electron microscope. Fine structural features of villous trophoblasts overlapped some villous stromal cells. In addition to the usual appearance of mature capillaries in villous stroma, we demonstrated and reported maturational stages of angiogenetic sprouts in term placenta. Extravillous trophoblasts were classified according to their location: fibrinoid, chorion, trophoblastic, column, maternal vascular endothelium, or decidua. All of these trophoblasts shared some ultrastructural features but also were distinct from each other. In decidua, it was noted that the endothelial lining of some vessels was invaded by a few endovascular trophoblasts with irregular microvilli. These cells shared some ultrastructural properties with both villous trophoblasts and stromal cells. Examination showed that angiogenesis was still present in term placentas and that trophoblasts, endothelial and stromal cells have very similar properties ultrastructurally, suggesting they represent transformational forms.