BackgroundInterleukin-25 has been implicated in the pathogenesis of asthma from studies on human asthmatics and in murine asthma models. ObjectivesIn this study, we hypothesized that chronic exposure of the airways to IL-25 alone is able to induce pathogenic changes observed in animal models of asthma. MethodsWe performed a detailed comparison of the dynamics of development of cellular infiltration, cytokine expression and airways remodelling and hyperresponsiveness in mice sensitized and challenged with OVA, a classical model of allergic asthma and those exposed to IL-25 alone. ResultsIntranasal challenge of BALB/c mice with IL-25 alone induced a delayed (compared with OVA-challenge), predominantly eosinophilic and lymphocytic infiltration into the airways lumen, along with increased production of Th2-type cytokines, chemokines and collagen, secretion of epithelial mucus, goblet cell hyperplasia, deposition of subepithelial collagen, airways smooth muscle cell hyperplasia and angiogenesis. Correspondingly, IL-25 as well as OVA challenge both induced airways hyperresponsiveness and increased lung tissue damping. In contrast, IL-25 exposure did not increase IgE or IgG(1) production. Conclusions and Clinical RelevanceThe data suggest that chronic airways exposure to IL-25 alone is sufficient to induce allergen- and IgE-independent, asthma-like airways inflammation, remodelling and hyperresponsiveness in mice. Thus, IL-25 is a key molecular target in asthma, irrespective of the coexistence of IgE-dependent mechanisms.