Asthma is a common chronic inflammatory condition which affects over 300 million people worldwide. Thickening of the subepithelial layer is a key feature of asthmatic airways and the extent of thickening has been correlated with severity of asthma and increased exacerbations. Recent epidemiological studies have shown a link between fungal sensitisation primarily with Aspergillus fumigatus (A. fumigatus) and exacerbations of asthma leading to increased morbidity and mortality. The airway epithelium acts as an initial defence barrier to inhaled allergens such as A. fumigatus and emerging evidence suggests that as well as orchestrating an allergic immune response, it initiates aspects of airway wall remodelling including subepithelial thickening. However, induction of a profibrogenic response by the airway epithelium following exposure to inhaled fungi associated with severe asthma has not been well documented. The epithelial expression and production of the profibrotic growth factors, TGF-Î²1, TGF-Î²2, IL-6, endothelin-1 and periostin, selected as implicated in the aetiology of asthma and their profibrotic activity, were investigated in response to both A. fumigatus spores and culture filtrate in vitro. Furthermore, in vivo chronic inhalation models using either live spores or culture filtrate from two different strains of A. fumigatus (AF293 and CEA10) were used to determine the ability of the fungi to induce murine airway wall remodelling. In vitro, spores from both strains were able to induce the expression and production of IL-6 and endothelin-1 from human bronchial epithelial cells but none of the other profibrotic growth factors. In vivo, despite spores from both strains inducing expression and production of IL-6 and endothelin-1, only CEA10 spores caused significant subepithelial collagen deposition however, both strains induced Î±-SMA, a myofibroblast and smooth muscle marker around the airways. As a secreted factor was suspected of driving airway wall remodelling, subsequent studies used culture filtrate produced by the two strains, AF293, a low and CEA10, a high protease producer in basal medium. Only AF293 culture filtrate induced IL-6 and endothelin-1 from human bronchial epithelial cells in vitro. However, in vivo, culture filtrate from both strains was able to induce IL-6 and endothelin-1 expression, with AF293 causing a more profound subepithelial collagen deposition and significantly increased Î±-SMA abundance. It was hypothesised that epithelial-derived endothelin-1 drives airway wall remodelling and hence Endothelin receptor A was inhibited in the in vivo culture filtrate inhalation model. A significant reduction in subepithelial collagen deposition and Î±-SMA localisation around the airways was demonstrated in mice receiving an Endothelin receptor A antagonist compared with culture filtrate alone. This thesis indicates that A. fumigatus exposure can drive features of airway wall remodelling such as subepithelial fibrosis possibly through the epithelial production of profibrotic growth factor, endothelin-1.