F3 and idiopathic pulmonary fibrosis: In patients with idiopathic pulmonary fibrosis (IPF), abnormal deposition of fibrin is found in the lung alveolar spaces [1], along with strong lung tissue expression of tissue factor, an initiator of blood coagulation, and plasminogen activator inhibitor-1 (PAI-1), an inhibitor of the fibrinolytic system [2].