Differentiation and secretory activities of cultured human placental cytotrophoblast.
Ultrastructural, autoradiographic, immunofluorescent and biochemical techniques were used to characterize primary cultures of term placental cytotrophoblast in order to gain insight into the differentiation and secretory capacities of the cellular component of human trophoblast. Trypsin treatment of placental villi allowed isolation of a predominantly cytotrophoblast cell population that maintained viability up to 13 weeks in monolayer culture. Autoradiographic studies of tritiated thymidine incorporation identified a smaller diameter mononucleated cell population that was mitotically active and developed into larger diameter mononucleated cells and into multinucleated cells during culture. Ultrastructurally, cultured cells formed desmosomes, had an extensive network of cytoplasmic microfilaments and contained the organelles for hormone synthesis and secretion. These cells secreted steroid hormones, secreted Schwangerschafts protein I, actively incorporated tritiated glycoprotein precursors and expressed surface immunoreactivity for the beta-subunit of human chorionic gonadotrophin (hCG). However, medium concentrations of hCG and human placental lactogen dropped rapidly to undetectable levels after 14 days in primary culture. Cells grown beyond confluence differentiated into 1 to 2 mm structures with a villus-like histology. Our studies indicate that cytotrophoblast can secrete steroids, cytotrophoblast differentiation occurs in vitro in the absence of maternal tissues, hCG synthesis occurs in cultured cytotrophoblast and medium concentrations of placental protein hormones are not the best indicators of cell viability for cultures of cytotrophoblast.