To investigate the relationship between these symptoms and lower airway inflammatory levels, we analysed Interleukin-8 (IL-8, a potent neutrophil chemoattractant) and Transforming Growth Factor-β1 (TGFβ-1, a protein important in wound repair, airway remodelling and the development of sub-epithelial fibrosis). This evidence concerns the gene CXCL8 and fibrosis.