SERPINA1 and pulmonary emphysema: Using the previously described low-dose PPE model of AAT-deficient emphysema (7), we performed a dose titration experiment using lung homogenate from AAT−/− mice administered 0.2 units of tracheal PPE and treated with IgG 2 mg/kg, KF4 2 mg/kg or KF4 0.5 mg/kg in a colorimetric elastase activity assay.