DDAH2 and chronic obstructive pulmonary disease: A number of studies have showed that there was a low grade systemic inflammation in patients with COPD, even in stable state, manifesting as elevated levels of acute phase proteins, circulating cytokines, and inflammatory cells.4 The systemic inflammation is correlated with reduced lung function,4 lower exercise capacity,5 increased risk of future acute exacerbations,6 increased risk of hospitalization,7 all-cause6-8 and COPD-related mortality.7 Also, the systemic inflammation is associated with increased risk of major comorbidities in COPD.9