Necrotic feature of the trophoblasts lacking HLA-G expression in normal and pre-eclamptic placentas.

PROBLEM: Human leukocyte antigen (HLA)-G is thought to be expressed in all placental extravillous trophoblasts (EXTs). In pre-eclamptic placentas, a lack of HLA-G expression on EXTs had been found, and deduced as a possible cause of pre-eclampsia. However, a subset of EXTs lacking expression of HLA-G can also be found in normal placenta. Therefore, we sought to compare these cells in normal and pre-eclamptic placentas. METHODS OF STUDY: Frozen sections of normal and pre-eclamptic placentas were examined by immunohistochemical staining using HLA-G monoclonal antibody 87G, histochemical enzymatic analysis of succinate dehydrogenase (SDH) and ultrastructural analysis.
RESULTS: A subset of EXTs lacking HLA-G expression was found in both normal and pre-eclamptic placentas. These cells showed necrotic features such as the swelling of cells, eosin-achromatophilia, the loss of SDH activity and swelling mitochondria. Cells from both tissues were identical with regard to these features.
CONCLUSION: The features of the EXTs lacking HLA-G expression indicated they had undergone necrosis and thus could not express HLA-G protein. Therefore, an alternative interpretation to the lack of HLA-G expression in pre-eclamptic placentas is that it is the result of cell death and not the cause.