Which statement about PAI-1 is correct?

Which statement about PAI-1 is correct?

• A. PAI-1 activates tPA.
• B. PAI-1 inhibits tPA.
• C. PAI-1 is a cofactor for APC.
• D. PAI-1 activates plasmin.

Answer: (B)

PAI-1 acts as a major brake on fibrinolysis by inhibiting tissue plasminogen activator. It is a serine protease inhibitor that binds tPA (and uPA), forming a stable complex that blocks their ability to convert plasminogen to plasmin. Since plasmin dissolves fibrin, inhibiting tPA reduces plasmin formation and slows clot breakdown. Therefore, the correct statement is that PAI-1 inhibits tPA. It does not activate tPA, it is not a cofactor for activated protein C (that role involves protein S with APC), and it does not activate plasmin—plasmin activation is driven by tPA/uPA, which PAI-1 inhibits.

PAI-1 acts as a major brake on fibrinolysis by inhibiting tissue plasminogen activator. It is a serine protease inhibitor that binds tPA (and uPA), forming a stable complex that blocks their ability to convert plasminogen to plasmin. Since plasmin dissolves fibrin, inhibiting tPA reduces plasmin formation and slows clot breakdown. Therefore, the correct statement is that PAI-1 inhibits tPA. It does not activate tPA, it is not a cofactor for activated protein C (that role involves protein S with APC), and it does not activate plasmin—plasmin activation is driven by tPA/uPA, which PAI-1 inhibits.