Impaired macrophage phagocytosis in non-eosinophilic asthma
Article first published online: 24 DEC 2012
© 2012 Blackwell Publishing Ltd
Clinical & Experimental Allergy
Volume 43, Issue 1, pages 29–35, January 2013
How to Cite
Cite this as: AMAZES Study Research Group, Clinical & Experimental Allergy 2013 (43) 29–35., , , , , ,
- Issue published online: 24 DEC 2012
- Article first published online: 24 DEC 2012
- Accepted manuscript online: 28 NOV 2012 12:48PM EST
- Manuscript Accepted: 11 JUL 2012
- Manuscript Revised: 25 JUN 2012
- Manuscript Received: 14 MAR 2012
Many patients with non-eosinophilic asthma have increased numbers of neutrophils in the airways. The explanation for this chronic inflammation remains unclear, but may result from an impaired ability of alveolar macrophages to phagocytose apoptotic cells (a process termed ‘efferocytosis’), as we have shown in chronic obstructive pulmonary disease (COPD).
To examine induced sputum as a non-invasive technique to characterize efferocytosis in chronic lung diseases and to compare efferocytosis in patients with non-eosinophilic asthma, eosinophilic asthma and COPD.
Participants with stable asthma (20 with eosinophilic and 30 with non-eosinophilic) and COPD (n = 11) underwent clinical assessment including allergy skin tests, saline challenge and sputum induction. Sputum cells were dispersed using dithiothreitol and resuspended in culture medium. Efferocytosis of apoptotic bronchial epithelial cells by sputum-derived macrophages was determined using flow cytometry.
There were no significant differences in efferocytosis between paired sputum and bronchoalveolar lavage macrophages from three subjects. Efferocytosis was significantly impaired in patients with non-eosinophilic asthma [mean (SD) 0.95 (0.24)] compared with eosinophilic asthma [1.17 (0.19)] and to a similar degree as patients with COPD [1.04 (0.16)]. Sputum neutrophils were significantly higher in patients with COPD and non-eosinophilic asthma compared with eosinophilic asthma.
Conclusion and Clinical Relevance
Induced sputum provides a reliable and non-invasive method for studying macrophage efferocytosis in chronic lung disease. Macrophage efferocytosis is impaired in non-eosinophilic asthma to a similar degree as that in COPD and may explain the persistent airway neutrophilia and chronic inflammation that characterizes this asthma subtype.