FPR1 and chronic obstructive pulmonary disease: COPD patients with a high MMRC score (≥ 2) had significantly higher cell surface FPR1 expressions on neutrophil than either those with a low MMRC score (8.0 ± 5.4 vs. 5.4 ± 1.8 MFI, p = 0.04) or healthy non-smokers (8.0 ± 5.4 vs. 4.3 ± 2 MFI, p = 0.006, Fig. 3e), while COPD patients with frequent moderate exacerbation in the past 1 year had lower FPR2 expression on neutrophil than either those without frequent moderate exacerbation (≥ 2 events in the past 1 year) (9.0 ± 2.4 vs. 14.8 ± 8.7 MFI, p = 0.007) or healthy non-smokers (9.0 ± 2.4 vs. 14.2 ± 4.9, p = 0.008, Fig. 3f).