Mast cells play a partial role in allergen-induced subepithelial fibrosis in a murine model of allergic asthma

Background Role of mast cells in the development of allergen-induced airway remodelling has not been fully investigated in vivo . Objective To clarify the possible role of mast cells in the development of allergen-induced airway remodelling, we compared their responses of genetically mast cell-deficient mice, WBB6F1-W/W-v (c-kit mutant) and Sl/Sl(d) (c-kit ligand mutant) mice with those of congenic normal mice in a murine model of allergic asthma. Methods Mice were sensitized to ovalbumin (OA) with alum, and exposed daily for 3 weeks to aerosolized OA. Twenty-four hours after the last inhalation, bronchial responsiveness to acetylcholine (Ach) was measured, and bronchoalveolar lavage (BAL), and biochemical and histological examinations were performed. Results In both sensitized mast cell-deficient mice, the degree of bronchial hyper-responsiveness to Ach, the number of inflammatory cells and the level of transforming growth factor-beta1 in BAL fluid, IgE response and goblet cell hyperplasia in the epithelium after repeated allergen provocation were not significantly different from those of congenic mice. In contrast, subepithelial fibrosis, evaluated in the fibrotic area around the airways, observed in congenic mice after repeated allergen challenge was partially attenuated in both mast cell-deficient mice. In addition, the amount of hydroxyproline in the lung of mast cell-deficient mice was significantly lower than that of congenic mice. Furthermore, the decreased fibrotic area and amount of hydroxyproline in W/W-v mice was completely recovered by reconstitution of tissue mast cells with bone marrow-derived mast cells of congenic mice. Conclusion These findings suggest that mast cells play a partial role in the development of allergen-induced subepithelial fibrosis, although airway inflammation, epithelial remodelling and BHR caused by repeated allergen challenge are independent of mast cells, at least in this model.