Plasminogen activator inhibitor-2 (placental PAI) is a coagulation factor that inactivates tPA and urokinase. It is present in most cells, especially monocytes/macrophages. PAI-2 exists in two forms, a 60-kDa extracellular glycosylated form and a 43-kDa intracellular form.
It is present only at detectable quantities in blood during pregnancy, as it is produced by the placenta, and may explain partially the increased rate of thrombosis during pregnancy. The majority of expressed PAI-2 remains unsecreted due to the presence of an inefficient internal signal peptide.