MPO and bacterial infectious disease: In particular, bacterial infections account for a significant fraction of all exacerbations (White et al., 2003) and have been reported to cause increased airway inflammation; biomarkers of inflammation such as MPO, neutrophil elastase activity, IL-8, and LTB4 levels all are positively related to sputum bacterial load in fresh sputum samples from COPD patients (Hill et al., 2000).