Lung tissue neutrophil (polymorphonuclear leukocyte) uptake was assessed via determination of myeloperoxidase activity. Lungs were dried and homogenized in 1.0 ml of PBS (50 mmol/L, pH 6.0) with 5% hexadecyl-trimethylammonium bromide and 5 mmol/L of EDTA. Homogenates were sonicated, centrifuged at 4 ϫ 10 4 g for 20 minutes and were frozen and thawed twice, followed by homogenization and centrifugation. The supernatant was mixed 1:30 (v/v) with assay buffer (0.2 mg/ml of o-dianisidine hydrochloride and 0.0005% H 2 O 2 ), and absorbance change was measured at 460 nm for 3 minutes. Myeloperoxidase activity based on dry lung weight was calculated as the change in absorbance over time. 15 