COPD exacerbation severity and frequency is associated with impaired macrophage efferocytosis of eosinophils

Eosinophilic airway inflammation is observed in 10-30% of COPD subjects. Whether increased eosinophils or impairment in their clearance by macrophages is associated with the severity and frequency of exacerbations is unknown.

Macrophage efferocytosis of eosinophils is impaired in COPD and is related to the severity and frequency of COPD exacerbations.

We categorised 103 COPD subjects into 4 groups determined by the upper limit of normal for their cytoplasmic macrophage red hue (<6%), an indirect measure of macrophage efferocytosis of eosinophils, and area under the curve sputum eosinophil count (≥ 3%/year). Eosinophil efferocytosis by monocyte-derived macrophages was studied in 17 COPD subjects and 8 normal controls.

There were no differences in baseline lung function, health status or exacerbation frequency between the groups: A-low red hue, high sputum eosinophils (n=10), B-high red hue, high sputum eosinophils (n=16), C-low red hue, low sputum eosinophils (n=19) and D- high red hue, low sputum eosinophils (n=58). Positive bacterial culture was lower in groups A (10%) and B (6%) compared to C (44%) and D (21%) (p=0.01). The fall in FEV1 from stable to exacerbation was greatest in group A (ΔFEV1 [95 % CI] -0.41 L [-0.65 to -0.17]) versus group B (-0.16 L [-0.32 to -0.011]), C (-0.11 L [-0.23 to -0.002]) and D (-0.16 L [-0.22 to -0.10]; p=0.02). Macrophage efferocytosis of eosinophils was impaired in COPD versus controls (86 [75 to 92]% versus 93 [88 to 96]%; p=0.028); was most marked in group A (71 [70 to 84]%; p=0.0295) and was inversely correlated with exacerbation frequency (r=-0.63; p=0.006). Conclusions: Macrophage efferocytosis of eosinophils is impaired in COPD and is related to the severity and frequency of COPD exacerbations.