Assessment of the phagocytic capability of sputum macrophages and neutrophils in COPD patients

<b>Background:</b> Defective macrophage phagocytosis has been shown in COPD using bronchoalveolar lavage and blood monocyte derived macrophages. The phagocytic capabilities of sputum macrophages and/or neutrophils in COPD are unknown. Sputum is a non-invasive sampling technique that can be performed at different disease states including exacerbation. We investigated phagocytosis in sputum macrophages and neutrophils from healthy controls and COPD patients at stable state. <b>Methods:</b> Phagocytosis of <i>Steptococcus Pneumoniae</i> or fluorescently labelled non-typeable <i>Haemophilus influenzae</i> (phRODO <i>NTHI</i>) by sputum macrophages and neutrophils was determined by gentamycin protection assay (n=5 COPD patients) or flow cytometry respectively in 14 COPD patients, 8 healthy smokers(HS) and 8 healthy non-smokers (HNS). Sputum macrophages and neutrophils were differentiated by adherence for the gentamycin protection assay or receptor expression (CD206 and CD66b respectively) by flow cytometry. <b>Results:</b> Using the gentamycin protection we observed a greater uptake of <i>Streptococcus Pneumoniae</i> by sputum neutrophils compared to sputum macrophages in COPD patients (p&lt;0.05). Flow cytometry showed greater uptake of phRODO <i>NTHI</i> by CD66b+ neutrophils compared to CD206+ macrophages in COPD patients and HS (p&lt;0.05) Uptake of phRODO <i>NTHI</i> by CD206+ macrophages was decreased in HS and COPD compared to HNS (p&lt;0.05). There was no differences in uptake of phRODO <i>NTHI</i> by CD66b+ neutrophils between groups. <b>Conclusion:</b> In these assays, sputum neutrophils showed more phagocytic activity than macrophages. Bacterial phagocytosis is impaired in sputum macrophages, but not sputum neutrophils, in COPD patients compared to HNS.