This project aimed to investigate whether the production of secretory IgA (S-IgA) is impaired in the CF lung, through which mechanisms, and whether this defect contributes to the pathogenesis of CF disease by impairing immunoprotection against respiratory pathogens such as Pseudomonas aeruginosa. The hypothesis was that pIgR (bronco-epithelial receptor poli Ig) expression is reduced in CF epithelia, as a result of CFTR-related epithelial changes and epithelial inflammatory damage; this might result in profound defects in the pIgR IgA system, leading to impaired IgA-mediated immune exclusion of respiratory pathogens, and thereby favouring chronic bacterial colonization and infections in CF. New data might pave the avenue toward improving lung mucosal defence against bacteria in patients with cystic fibrosis.