Localization of Type 1 plasminogen activator inhibitor in early decidua basalis and its role in pregnancy maintenance.

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor that controls trophoblast invasion by inhibiting fibrinolysis at the feto-maternal interface. This study aimed to compare PAI-1 expression patterns in decidual cells between different abortion types and investigate the role of PAI-1 in early pregnancy. Missed abortion (n = 22) and incomplete abortion (n = 16) cases were compared with induced abortion serving as normal pregnancy control (n = 16). PAI-1 localization and expression levels were evaluated using immunohistochemistry. PAI-1 was distributed in the cytoplasm of decidual cells. In addition, many PAI-1-positive cells were observed in the decidua basalis just under the Nitabuch fibrinoid layer, where many extravillous trophoblasts (EVTs) invaded. The percentage of PAI-1-positive decidual cells was not reduced in missed abortion (49.7 ± 29.6%) but was significantly reduced in incomplete abortion (11.6 ± 12.6%) compared to induced abortion as control (44.4 ± 10.9%). The significant reduction of PAI-1-positive decidual cells in incomplete abortion, which is characterized by bleeding, suggests that PAI-1 deficiency may cause excessive fibrinolysis leading to this clinical outcome.