Contact patterns between cytotrophoblast and decidual cells in human implantation site

To elucidate the mechanism of trophoblastic invasion, implantation sites removed from human uteri of early gestational stages of 7 to 10 week were investigated by electron microscopy. Almost all trophoblast cells which penetrated the fibrinoid layer and invaded into decidual tissue were cytotrophoblast cells, and abundant close-contacts between the cytotrophoblast and decidual cells were recognized in this site. The close-contact patterns which were composed of simple apposition, cytoplasmic projection from both cells and mixture of those without fusion were classified into five types. At the time of close-contact, the decidual cells showed the altered structures in various degrees, but never did they alter so strongly as to appear to have died completely. Thus, it is deduced that the influence from cytotrophoblast cells did not cause the destruction of the decidual cells but only biological inactivation of the cells. It is of great significance to the immunological problem between fetus and mother that the cytotrophoblast cells which are fetal epithelial cells can be in close-contact with decidual cells which are maternal stromal cells. Further confirmation relating to the production and transcellular transfer patterns of the information materials should be awaited in future.