Exposure to chlorine gas (Cl2) is one of the most common causes of irritant induced asthma (IIA). This exposure results in oxidative stress, damage to the airway epithelia, airway hyperresponsiveness (AHR), and neutrophilia. We hypothesized that increased AHR and oxidative stress are a direct result of neutrophil presence in the lungs following a single Cl2 exposure.
We exposed male Balb/C mice to 100ppm Cl2 for 5 minutes. Oxidative stress in lung tissue was evaluated for anti-oxidant genes by qPCR, and by nuclear factor (erythroid-derived 2)-like 2 (NRF2) nuclear translocation by immunofluorescence. Pulmonary neutrophils were quantified by immunohistochemistry. Neutrophils, eosinophils, and macrophages were depleted using anti-Gr1 antibody (100 μg/mouse), TRFK5 (100 μg/mouse) or clodronate-loaded liposomes (250 μg), respectively. AHR was evaluated with a constant phase model in response to inhaled aerosolized methacholine (6.25-50mg/ml).
Cl2 induced neutrophilia at 6h and 24h over baseline (by 10-fold and 5-fold, respectively) as well as increased expression of NRF2 mRNA and superoxide dismutase-1 (3-fold and 2.5-fold, respectively). The depletion of neutrophils eliminated the AHR induced by Cl2 in large, conducting airways and completely abolished increases in gene expression and NRF2 nuclear translocation. Depleting eosinophils or macrophages did not prevent Cl2 induced AHR.
Cl2 induced neutrophilia increases AHR by molecular and mechanical mechanisms by increasing oxidative stress and occupying space in large airways.