Patterns of bcl-2 expression in placenta

A total of 39 placentas, whose gestational ages ranged from 8 to 41 weeks, were analyzed for bcl-2 expression using immunohistochemistry and immunoblotting. Immunobistochemically, both intracytoplasmic and nuclear expression of bcl-2 was observed in villous and extravillous trophoblasts, villous mesenchymal cells and capillary endothelial cells, villous macrophages, intermediate trophoblasts, amnionic epithelium, and even in decidua and endometrial glandular epithelium in early gestational periods. The degree of expression significantly decreased in the placentas after the gestational period of 32 weeks which coincides with the declining phase of placental increase. On immunoblotting lysates of 104 cells from single cell suspensions of fresb placentas, bcl-2 was detected in the placentas of 22 and 33 gestational weeks, but it was negligible or absent in three term placentas. The results of the present study suggest two possible implications on the role of bcl-2 in placenta: 1) it may be a type of proliferation or maturation-related marker, especially of trophoblasts, which show decreased expression along with terminal differentiation and maturation, and 2) because the primary role of bcl-2 is the inhibition of programmed cell death (PCD), the decrease in placental bcl-2 around term may be a parturition-associated biological change.