The difficulty in obtaining a preparation of pure trophoblast cells for culture can be appreciated by understanding the structure of the placenta. The outer surface of the chorionic villi is covered by the syncytiotrophoblast, underlying which is a single cell layer of cytotrophoblast cells that sits on the basement membrane. Microvascular vessels connect this cell layer to the umbilical arteries and vein. The apical membrane of the syncytiotrophoblast is folded into numerous microvilli, and this layer forms a syncytium. Disaggregation of this villous tissue results in a broken syncytial membrane, releasing not only the cytotrophoblastic cells, but also the rest of the villous cell population (i.e., Hofbauer cells or macrophages, fibroblasts, grant cells, some adhering decidual and endothelial cells) as well as DNA from the nuclei of the syncytium. Separation of trophoblast from this heterogeneous cell population has proven to be a challenge.
