Eosinophils Are Dispensable for Allergic Remodeling and Immunity in a Model of House Dust Mite-induced Airway Disease

Rationale: Current thinking accredits eosinophils with preeminent contributions to allergic airway responses, including a major role in the development of airway remodeling, a process thought to significantly contribute to airway dysfunction. However, direct evidence in support of this notion is limited and often controversial. Objectives: We elucidated the requirement for eosinophils in the generation of allergic sensitization, airway inflammation, and remodeling in a model involving chronic respiratory exposure to house dust mite (HDM). Methods: We used three methods to selectively eliminate eosinophils, a depleting antibody (anti-CCR3), and two strains of eosinophil-deficient mice (Delta dbIGATA and the transgenic line PHIL). Measurements and Main Results: Anti-CCR3 treatment markedly reduced pulmonary eosinophilia (> 80%) over the course of HDM exposure but had no effect on the remaining inflammatory response, the extent of lung Th2 cells, or the development of remodeling-associated changes, including subepithelial collagen deposition and smooth muscle thickening. In addition, we observed that, despite the absence of eosinophils, HDM-exposed GATA mice mounted robust airway and lung inflammation and hyperresponsiveness and showed a remodeling response equivalent to that observed in wild-type mice. Moreover, these mice had similar serum HDM-specific IgE levels and Th2-associated splenocyte cytokine production as HDM-exposed wild-type control mice. Similar observations were made in PHIL eosinophil-deficient mice subjected to chronic HDM exposure, although slight decreases in airway mononuclear cells, but not lung Th2 cells, and remodeling were noted. Conclusions: Collectively, these data demonstrate that, at variance with the prevailing paradigm, eosinophils play negligible roles in the generation of HDM-induced allergic immunity and airway remodeling.