Background and objectives Lung remodelling is a recognized feature of chronic asthma. In the present study, we have used IL‐5‐deficient mice to evaluate the role of this cytokine and eosinophilic inflammation in the initial stages of the structural changes occurring in the lung after antigen challenge.

Methods Ovalbumin‐sensitized wild type and IL‐5‐deficient mice were daily challenged for 5 consecutive days and killed 3 or 7 days after the last challenge to study the inflammatory and remodelling events, respectively.

Results Wild type mice challenged with ovalbumin exhibited an accumulation of eosinophils in the bronchoalveolar lavage (BAL) fluid, associated with a production of BAL cellular fibronectin. Histological analysis also revealed an antigen‐specific increase in epithelial and alveolar cell proliferation together with an increase in mucus producing epithelial cells. Eosinophilic infiltration and the associated lung remodelling were totally abrogated in IL‐5‐deficient mice. In wild type mice, treated intranasally with 1 µg of murine IL‐5 for 5 consecutive days, no BAL eosinophilia and structural changes of the lungs could be observed.

Conclusion Our results demonstrate that eosinophil accumulation, but not IL‐5 alone, plays a central role in the initial stages of the lung remodelling process and suggests that therapies directed at inhibiting eosinophilic inflammation may be beneficial in treating chronic asthma.