Eosinophilic airways inflammation in Chronic Obstructive Pulmonary Disease
2015-07-09T13:31:02Z (GMT) by
Background: Eosinophilic airway inflammation (>3% sputum eosinophils) is a feature of subgroup of subjects with chronic obstructive pulmonary disease (COPD). My objectives were to investigate the clinical characteristics of eosinophilic COPD, its stability over time and extent in bronchial tissue, whether it is related to parasite exposure or atopy and whether its persistence is due to abnormal clearance by macrophages. Methods: Subjects were studied that had participated in previous observational studies. The repeatability of sputum eosinophils was measured between 3 monthly visits for 1 year. The extent of eosinophilic inflammation in bronchial tissue was assessed using immunohistology on bronchial tissue from COPD and control subjects. Positive serology for parasites was tested in serum samples for 4 helminth species. Atopy was assessed in the subjects using serum total Ig-E and skin prick test. Eosinophil efferocytosis by macrophages was investigated in vivo using cytoplasmic area of red hue of macrophages and in vitro using apoptotic eosinophils fed to monocyte-derived macrophages from COPD and healthy controls. The dynamics of eosinophil clearance during exacerbations was explored using the red hue technique. Results: Eosinophilic and non-eosinophilic COPD have similar lung function and exacerbation frequency. In eosinophilic COPD the health status is better and bacterial colonisation is lower. This phenotype is stable over time. Airway tissue eosinophilis are increased in COPD subjects with high blood eosinophils and are positively correlated with features of remodelling. Eosinophilic COPD is not associated with helminth exposure, but is related to elevated total Ig-E. Macrophage efferocytosis of eosinophils is impaired in COPD and is associated with the severity and frequency of COPD exacerbations. Efferocytosis of eosinophils by macrophages is increased following oral corticosteroid therapy at exacerbation. Conclusion: Eosinophilic COPD is a distinct and stable phenotype that persists in the blood, bronchus and sputum. Its persistence is partly related to atopy and impaired clearance by macrophages with the latter associated with COPD exacerbation severity and frequency.