The effects of inhaled house dust mite on airway barrier function and sensitivity to inhaled methacholine in mice

Turi GJ, Ellis R, Wattie JN, Labiris NR, Inman MD. The effects of inhaled house dust mite on airway barrier function and sensitivity to inhaled methacholine in mice. Am J Physiol Lung Cell Mol Physiol 300: L185-L190, 2011. First published November 5, 2010; doi:10.1152/ajplung.00271.2010.-Asthma is functionally characterized by increased airway sensitivity and reactivity. Multiple mechanisms are believed to underlie these functional disorders, including impairment of airway wall barrier function. One proposed mechanism of impaired barrier function is through the direct consequence of proteolytic properties of inhaled allergens, including house dust mite (HDM). Here, we have observed the direct effects of HDM on airway barrier function and response to nebulized or intravenous methacholine. HDM naive BALB/c mice were anesthetized, exposed to intranasal or intratracheal HDM (15 or 100 mu g), and allowed to recover for 30 min or 2 h before methacholine challenge. A separate group of mice was exposed to intratracheal poly-L-lysine (PLL; 100 mu g) for a duration of 30 min. This group served as a positive control for the presence of impaired barrier function and airway hypersensitivity. Negative control mice received saline challenges. Outcomes included assessment of lung mechanics in response to nebulized or intravenous methacholine as well as clearance of intratracheally instilled technetium-labeled (Tc-99m) DTPA to evaluate airway epithelial barrier function. We found that PLL produced a leftward shift in the dose-response curve following nebulized but not intravenous methacholine challenge. This was associated with a significantly faster clearance of Tc-99m-DTPA, indicating impairment in airway barrier function. However, HDM exposure did not produce changes in these outcomes when compared with saline-exposed mice. These findings suggest that direct impact on airway barrier function does not appear to be a mechanism by which HDM produces altered airway sensitivity in airway disease.