Problem: The low frequency of maternal immune responses to paternally inherited fetal antigens raises the following question: What regulates the immunobiology of pregnancy? Data suggest that this state is the result of peripheral immune-tolerance, an active process of immune-regulation in which activated T cells undergo apoptosis. We studied Fas ligand (FasL) expression and apoptosis in normal and pathologic placentas to find out whether the Fas-FasL-induced apoptosis takes place during implantation.
Method of study: FasL expression in paraffin sections was detected using specific antibodies and confirmed with reverse transcriptase-polymerase chain reaction of total RNA from frozen placentas. Apoptosis was detected using the terminal deoxy (d)-UTP nick end-labeling assay.
Results: FasL was found in the normal placenta and in gestational trophoblastic disease. Apoptotic leukocytes were localized to the maternal-fetal interface corresponding in localization with the distribution of FasL.
Conclusions: We propose that FasL expression in the placenta is a mechanism responsible for the development of maternal immune tolerance specific for paternal alloantigens and operates in pathologic states characterized by trophoblastic invasion/proliferation.