Plasminogen activator inhibitor-2 (placental PAI, SerpinB2, PAI-2) is a serine protease inhibitor of the serpin superfamily coded by the SerpinB2 gene on chromosome 18.q22.1. It acts as a coagulation factor that irreversibly inactivates tissue plasminogen activator and urokinase. PAI2 exists as a 60-kDa extracellular glycosylated form and a 43-kDa intracellular form. PAI2 protein is normally not detectable in adult plasma. The protein is produced at large quantities in the placenta which explains that PAI2 is detectable in blood only during pregnancy. PAI2 may thus contribute to the increased rate of thrombosis during pregnancy. PAI2 can bind to multiple intracellular and extracellular proteins. For example, it was suggested that PAI2 may activate p53 and stabilize p21. Macrophage derived PAI2 plays a role in inflammatory responses and infections, potentially in downregulating T cells that secrete IgG2c and interferon type II. Although glycosylated extracellular PAI2 regulates fibrinolysis, it remains unclear whether this is the main or entire role of PAI2. PAI2 is predominantly intracellular but specific intracellular roles for PAI2 have not yet been identified. PAI2 may play a complex role in cancer. Both tumor-promoting and tumor-inhibiting effects have been described.