Apoptotic nuclei within the uterine decidua of first trimester pregnancy arise from CD45 positive leukocytes

PROBLEM: The Fas/Fas-ligand (FasL) system is discussed to be one of the mai n components responsible for the formation and maintenance of an immune pri vilege. As we were able to detect FasL on fetal trophoblast cells infiltrat ing the maternal uterine tissue and Fas on decidual leukocytes (Hammer et a l., Am J Reprod Immunol, 1999: 41: 41-51), we investigated whether apoptosi s occurs in the maternal decidua during the first trimester of pregnancy. METHOD OF STUDY: A TUNEL-assay was performed in combination with immunofluo rescence to detect and characterize cells undergoing apoptosis. RESULTS: Apoptotic nuclei mainly arising from CD45(+) leukocytes could be d etected in the trophoblast-invaded decidua basalis as well as in the non-in vaded decidua parietalis. However, while in the decidua parietalis the apop totic leukocytes are scattered within the whole functional stroma, in the d ecidua basalis they are concentrated in the area around the so-called "necr otic foci" and especially in the primary fete-maternal contact zone, where trophoblast cells from the cell columns begin to invade the maternal tissue . CONCLUSION: Because of the irregular distribution of apoptotic CD45(+) leuk ocytes in the decidua basalis we think that some of the maternal leukocytes are activated and killed by fetal trophoblast cells which express FasL.