Vacuolated Cytotrophoblast: A subpopulation of trophoblast in the chorion laeve

In summary, immunocytochemical analysis of the placenta and fetal membranes discloses two subpopulations of trophoblastic cells in the chorion laeve with distinct morphologic and immunocytochemical features. Both subpopulations are composed of mononucleate cells but one contains clear vacuolated cytoplasm whereas the other contains non-vacuolated eosinophilic cytoplasm. The vacuolated cells are placental alkaline phosphatase (PLAP) positive and human placental lactogen (hPL) negative, whereas the eosinophilic cells are PLAP negative and hPI, positive. Both cell types contained immunoreactive keratin and epithelial membrane antigen, but are negative for human chorionic gonadotropin(β), pregnancy specific beta i-glycoprotein, and prolactin. Electron microscopic studies of the vacuolated cells show that these cells contain numerous lucent non-membrane bound lipid droplets and pinocytotic vesicles. In addition they contain numerous intracellular filaments and desmosomes corresponding to the immunocytochemical localization of keratin. Their precise function is not clear, but the abundance of PLAP, an enzyme associated with absorption, suggests that these cells may be involved with maternal fetal transport. The vacuolated cells appear to be limited to the chorion. Their characteristic morphologic and immunocytochemical features and unique anatomic distribution suggests that they represent a distinctive subpopulation of trophoblastic cells for which we propose the term 'vacuolated cytotrophoblast'.