INTERMEDIATE CELLS DURING CYTOTROPHOBLAST DIFFERENTIATION INVITRO

Differentiation of the human placental trophoblast cell involves a mul tistep process, with the generation of several distinct types of inter mediate cytotrophoblast cells. Using a short term in vitro cell cultur e system and centrifugal elutriation, we studied the isolation and mor phological and biochemical differentiation of these separated intermed iate cell populations. Freshly isolated cell fractions, incubated for 24 h, are heterogeneous in their differentiation stages as determined by the secretion of the proteins chorionic gonadotropin alpha and beta , human placental lactogen, and pregnancy specific beta1-glycoprotein. Maintenance in cell culture allows for the further differentiation of these intermediate cells and for syncytium formation. With the use of sequential trypsinizations, our data also suggest the parallel differ entiation of cytotrophoblast cells into two distinct subsets: one whic h, through differentiation, gets committed to syncytium formation, and the other, which remains mononuclear despite high degrees of biochemi cal differentiation. These latter cells retain the capacity for syncyt ium formation when reintroduced into appropriate culture conditions. T hese findings refine the use of the term 'intermediate cell'' by previ ous investigators. We suggest that our in vitro system defines normal intermediate stages of trophoblast differentiation, and also serves as a model to simulate adverse conditions of syncytial degeneration or i njury.