Chronic bronchial allergic inflammation increases alveolar liquid clearance by TNF-α-dependent mechanism

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Abstract
Bronchial inflammation in allergic asthma is associated with active exudation from the bronchial tree into the interstitial space of both mucosa and submucosa. The aim of this study was to evaluate epithelial and endothelial permeability as well as alveolar fluid movement in a model of chronic allergic inflammation in Brown-Norway rats sensitized and challenged with ovalbumin (OA). Control groups were challenged with saline solution (C), and rats were immunized by OA but not challenged (Se). Lung sections showed a marked inflammatory infiltrate associated with perivascular and peribronchiolar edema in OA. To measure alveolar liquid clearance, a 5% bovine albumin solution with 1 μCi of125I-labeled human albumin was instilled into the air spaces. Alveolar-capillary barrier permeability was evaluated by intravascular injection of 1 μCi of 131I-labeled albumin. Endothelial permeability was significantly increased in OA, from 0.08 ± 0.01 in the C group to 0.19 ± 0.03 in OA group ( P < 0.05). Final-to-initial protein ratio was also statistically higher in OA (1.6 ± 0.05) compared with C (1.38 ± 0.03, P = 0.01) and Se groups (1.42 ± 0.03, P = 0.04). Administration of anti-tumor necrosis factor-α antibodies within the instillate significantly decreased this ratio (1.32 ± 0.08, P = 0.003 vs. OA). To conclude, we demonstrated a tumor necrosis factor-α-dependent increase in alveolar fluid movement in a model of severe bronchial allergic inflammation associated with endothelial and epithelial leakage.