Immunohistochemical evidence of HLA-G expression in extravillous trophoblast invading decidual tissues

HLA-G is a non classical HLA I gene product involved in the regulation of implantation and in the immune tolerance during pregnancy, by modulating maternal immune responses at the fetal-maternal interface. In pregnancies lacking immune tolerance and ending in miscarriage, the expression of HLA-G is very probably defective or altered. In order to contribute to further investigations about HLA-G expression in autoimmune miscarriages, we have tried to describe HLA-G immunohistochemical patterns of expression in a homogeneous cohort of normal first trimester choriodecidual specimens, in the three different extravillous trophoblast (EVT) populations ("cell islands", "cell columms", and intravascular EVT cells). We expected to demonstrate HLA-G reactivity to the tested antibody (MEMG/01) in all three populations. All choriodecidual specimens were histologically and clinically reviewed to exclude any pathologic finding. Immunohistochemical identification of trophoblast cells in the selected specimens was performed via wellknown immunostains such as Cytokeratin 8/18 (CAM5.2) and NCL-PLp; anti-Ki67 was also used to point out proliferating EVT cells. Then, MEM-G/01 was tested at various dilutions, with or without pretreatment, to find the optimal protocol. As expected, HLA-G specifically stained all three EVT populations, with decreasing reactivity from EVT cell islands to EVT cell columns or intravascular EVTs. The next step will be the investigation of HLA-G pattern of expression in autoimmune aborters.