Plasminogen activator inhibitor 1 (PAI-1) is overexpressed in pleural fluids in empyema by up to three orders of magnitude [32,33,34], and is the most effective mechanism-based inhibitor (serpin) of tissue (tPA) and urokinase (uPA) plasminogen activators [35,36]—therapeutics used for IPFT [37,38]. Here, SERPINE1 is linked to empyema.