Prolongation of neutrophil survival by the culture supernatant of Pseudomonas aeruginosa

Background and objectives: The pathogenesis of airway inflammation in diffuse panbronchiolitis (DPB) is unknown. Neutrophil survival-enhancing activity, partially mediated by granulocyte-macrophage colony-stimulating factor (GM-CSF), has been shown in the sputum from DPB patients. This study investigated the mechanisms of GM-CSF expression in the airways of DPB patients. This involved examining the effects of mucoid Pseudomonas aeruginosa strains derived from chronically colonized patients with DPB on neutrophil survival and GM-CSF expression. Methods: Neutrophils from healthy subjects were cultured with the culture supernatants of P. aeruginosa isolated from sputum of DPB patients in the presence or absence of anti-GM-CSF and anti-GM-CSF receptor (α chain) antibodies, and viable neutrophils were counted daily. GM-CSF gene expression in neutrophils was evaluated by RT-PCR. Results: Neutrophils cultured with the culture supernatants showed significantly prolonged survival, compared with neutrophils cultured with the control broth. The neutrophil survival-enhancing activity in the culture supernatants was lost by heating. The enhanced survival of neutrophils was abolished in the presence of anti-GM-CSF and anti-GM-CSF receptor (α chain) antibodies. GM-CSF mRNA was detected in neutrophils cultured with the bacterial supernatants, but not in those with the control broth. Conclusion: P. aeruginosa-derived factors (rich in proteins) stimulated neutrophils to synthesize GM-CSF, which enhanced neutrophil survival in an autocrine/paracrine fashion.