Immunohistochemical localization of urokinase-type plasminogen activator and the plasminogen activator inhibitors 1 and 2 in early human implantation sites.

Objective: Our purpose was to immunolocalize urokinase-type plasminogen activator and the plasminogen activator inhibitors 1 and 2 in human implantation sites, with emphasis on the types of trophoblast expressing the plasminogen activator and the inhibitors.

Study Design: Urokinase and the plasminogen activator inhibitors 1 and 2 were localized immunohistochemically in early human implantation sites in unruptured ectopic pregnancies from patients in an in vitro fertilization program.

Results: Urokinase kinase and the plasminogen activator inhibitors 1 and 2 were localized in the cytoplasm of cytotrophoblasts and in the cytoplasm and plasma membranes of intermediate and syncytiotrophoblast. Greater staining was noted in nonvillous, relative to villous, cytotrophoblasts for urokinase and both inhibitors.

Conclusions: Urokinase-type plasminogen activator and the plasminogen activator inhibitors 1 and 2 were localized in all three forms of trophoblast at the maternal-fetal interface in early human implantation sites, particularly the differentiated and invasive forms of trophoblast. These results support a role for the plasminogen activator or inhibitors in the controlled invasion of the maternal decidua by the trophoblast during human implantation.