Airway neutrophilia in COPD is not associated with increased neutrophil survival

P. Rytilä ^1*, M. Plataki ², F. Bucchieri ², M. Uddin ², G. Nong ², V.L. Kinnula ³, R. Djukanovi ²

¹ Division of Infection, Inflammation and Repair, University of Southampton, Southampton, United Kingdom; and Division of Allergy, Dept of Medicine, Helsinki University Central Hospital, Helsinki, Finland
² Division of Infection, Inflammation and Repair, University of Southampton, Southampton, United Kingdom
³ Division of Respiratory Diseases, Dept of Medicine, Helsinki University Central Hospital, Helsinki, Finland

^* To whom correspondence should be addressed. E-mail: paula.rytila{at}hus.fi.

	Abstract

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. We wanted to assess whether neutrophil pro-survival mechanisms are increased in the airways of subjects with COPD due 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. The 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-7AAD staining. COPD-patients and healthy smokers had a significantly higher percentage of sputum neutrophils than healthy controls (p<0.0001, p=0.01). 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. Prolonged survival of neutrophils in sputum is not a feature of COPD and cannot explain the increased numbers of airway neutrophils in this disease.