Granulocyte activation markers in induced sputum: comparison between chronic obstructive pulmonary disease, asthma,...

Airway inflammation is present in asthma and is thought to play a significant part in the development of airflow obstruction. In chronic obstructive pulmonary disease (COPD), neutrophilic inflammation is present in the airway lumen, whereas the submucosa displays a lymphocytic infiltrate. Less is known about the nature and mechanisms of inflammation in COPD than in asthma. Induced sputum allows noninvasive sampling of respiratory tract secretions from patients and control subjects, allowing characterization of cells and measurement of soluble markers. We exploited this technique in order to compare the presence and quantify specific markers of eosinophil and neutrophil activation in subjects with asthma or COPD, and control subjects. Differential cell counts showed significantly higher neutrophil percentages in the patients with COPD compared with other groups, while patients with asthma had higher numbers of eosinophils. The neutrophil markers myeloperoxidase (MPO), from primary granules in neutrophils, and human neutrophil lipocalin (HNL), released from secondary granules, were elevated in patients with asthma and COPD compared with control subjects but markedly more so in COPD. The difference between COPD and asthma was more marked for HNL than for MPO suggesting that HNL may be a better marker for discriminating between these conditions. Concentrations of the eosinophil granule protein, eosinophil cationic protein (ECP), and the eosinophil granule-derived enzyme, eosinophil peroxidase (EPO) were raised in the patients with asthma and those with COPD.