• Apoptosis;
  • pregnancy;
  • reproductive immunology;
  • TUNEL-assay;
  • uterus

PROBLEM: The Fas/Fas-ligand (FasL) system is discussed to be one of the main components responsible for the formation and maintenance of an immune privilege. As we were able to detect FasL on fetal trophoblast cells infiltrating the maternal uterine tissue and Fas on decidual leukocytes (Hammer et al., Am J Reprod Immunol, 1999; 41: 41–51), we investigated whether apoptosis occurs in the maternal decidua during the first trimester of pregnancy.

METHOD OF STUDY: A TUNEL-assay was performed in combination with immunofluorescence to detect and characterize cells undergoing apoptosis.

RESULTS: Apoptotic nuclei mainly arising from CD45+ leukocytes could be detected in the trophoblast-invaded decidua basalis as well as in the non-invaded decidua parietalis. However, while in the decidua parietalis the apoptotic leukocytes are scattered within the whole functional stroma, in the decidua basalis they are concentrated in the area around the so-called “necrotic foci” and especially in the primary feto–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+ leukocytes in the decidua basalis we think that some of the maternal leukocytes are activated and killed by fetal trophoblast cells which express FasL.