Isolation of endothelial cells from human term placental villi using immunomagnetic beads

Chorionic villi excised from freshly delivered human term placentae and small endothelial cell aggregates were released from them by the sequential use of collagenase and trypsin. The endothelial cells were further isolated by rosetting with magnetic polystyrene beads which were coated with QB END/40, the endothelial-specific monoclonal antibody (mAb) to thrombomodulin. Cell rosettes were plated on gelatin coated Petri dishes. The cells initially grew as discrete colonies but reached confluence within 7 days. The monolayers were sub-cultured five times, and grew to confluence each time. All the cells were immunoreactive to the endothelial markers von Willebrand factor, QB-End/40 and Ulex europaeus-1 lectin. They did not show immunoreactivity to trophoblast markers (mAbs ED341 and ED235). The isolated cells could also incorporate acetylated low-density lipoprotein. Most of the cells possessed an elongated morphology, though some were slightly spread and polygonal in shape. The cell monolayers did not resemble the typical cobblestone appearance of endothelial cells isolated from large vessels. Ultrastructurally, most of the cells resembled placental microvascular cells in shape and frequency of caveolae; undifferentiated cell-cell contacts and extracellular matrix material was observed. Human placental microvascular endothelial cells may offer an in vitro model which complements the use of the perfused term placental lobule in studies of microvascular permeability.