Airway neutrophilia in COPD is not associated with increased neutrophil survival

Neutrophilic airway inflammation is a prominent feature of chronic obstructive pulmonary disease (COPD) and correlates with disease severity. The mechanisms that determine the extent of neutrophilia could involve increased influx or prolonged survival of neutrophils. The aim of the study was to assess whether neutrophil pro-survival mechanisms are increased in the airways of subjects with COPD owing to the presence of anti-apoptotic factors in the bronchial lining fluid. Induced sputum samples were collected from 20 subjects with stable COPD, 14 healthy smokers and 14 healthy controls. Quantification of apoptotic neutrophils was based on typical morphological cell changes. Anti-apoptotic, pro-survival activity in the sputum was studied by culturing peripheral blood neutrophils with the fluid phase of induced sputum. Apoptosis was assessed both by morphology and flow cytometry using Annexin V/7-aminoactinomycin D staining. COPD patients and healthy smokers had significantly higher percentages of sputum neutrophils than healthy controls. However, there were no significant differences between the three subject groups in either the proportion of apoptotic neutrophils in sputum or the in vitro anti-apoptotic activity detected in the sputum fluid phase. In conclusion, prolonged survival of neutrophils in sputum is not a feature of chronic obstructive pulmonary disease and cannot explain the increased numbers of airway neutrophils in this disease.