Apoptotic cells in the human endometrium and placental villi: pitfalls in applying the TUNEL method

Apoptotic cells were histochemically demonstrated by the TdT-mediated biotinylated dUTP nick end-labeling (TUNEL) method in formalin-fixed and paraffin-embedded sections of the human endometrium and placental villi. In 53 endometrial biopsy specimens, labeled nuclei were identified in 16 samples showing a desquamating change, associated with menstruation, functional bleeding or adenocarcinoma. Cells in the normal proliferative and secretory phases were unlabeled. The labeled nuclei in the gland and stroma corresponded well to the so-called apoptotic bodies. Placental tissues at various stages of gestation were obtained by spontaneous abortion, intrauterine fetal death or normal delivery. Syncytiotrophoblastic cells in an early gestational stage (7-12 weeks) and in the term placenta were focally labeled, and the labeled cells possessed pyknotic nuclei and densely eosinophilic cytoplasm. In the early gestational chorionic villi with marked hydropic degeneration or in hydatidiform mole, the stromal cells were frequently labeled. Villous cells in coagulation necrosis (infarction) also revealed strong signals. The apoptotic bodies were not recognizable histologically in these labeled villi. The placenta at the 20th to 33rd week of gestation lacked labeling. From a technical point of view, it should be noted that cells in the foci showing ischemia or coagulation necrosis were labeled positively.