Neutrophils enhance expression of inducible nitric oxide synthase in humannormal but not cystic fibrosis bronchial epithelial cells

The bronchial epithelium in cystic fibrosis (CF) expresses very low levels of the inducible form of nitric oxide synthase (iNOS). The product of iNOS, nitric oxide (NO), mediates anti-microbial effects and earn reduce neutrop hil sequestration in the lung, Heavy neutrophilic infiltration of the pulmo nary epithelium is a major feature of the end-stage CP: lung. This study hy pothesized that the system whereby the pulmonary epithelium protects itself against exaggerated neutrophilic infiltration by producing NO is compromis ed in CF. Human neutrophils were activated by incubation with cytokines, ad ded to monolayers of normal (16HBE14o-) and CF (CPEE41o-) bronchial epithel ial cells and co-cultured for up to 72 h. Marked up-regulation of iNOS prot ein expression was seen in normal bronchial epithelial cells following neut rophil co-culture but the CF cells showed a significantly smaller increase (p < 0.001). To determine whether the relative lack of protein was due to a defect in translation, RT-PCR of iNOS mRNA was carried out and a pattern o f mRNA expression was seen paralleling that of the protein, The reduced pro duction of NO by CF compared with normal epithelium was shown by the presen ce of significantly (p < 0.001) less accumulated nitrites in medium after c o-culture with neutrophils, in summary, this study shows that the normal pr oduction of NO by bronchial epithelium in response to contact with neutroph ils is lacking in CP. As NO has been shown to oppose neutrophil sequestrati on, its relative lack in CF may underlie the heavy neutrophilic infiltratio n that characterizes the disease. Copyright (C) 2000 John Wiley & Sons, Ltd .