Airway inflammation in chronic obstructive pulmonary disease: comparisons with asthma

Chronic obstructive pulmonary disease (COPD) is a progressive syndrome of expiratory airflow limitation caused by chronic inflammation of the airways and lung parenchyma. The airway inflammatory response in COPD is initiated by smoking in the overwhelming majority of cases, and chronic exposure to cigarette smoke initiates a series of events that causes damage to central airways, peripheral airways, and terminal airspaces, leading to physiologic and clinical abnormalities. Although COPD shares some clinical features with asthma, another prevalent airway inflammatory disease, there are distinct differences in the phenotypic characteristics of airway inflammation between COPD and asthma. The eosinophil is the most prominent inflammatory cell in asthma, with mast cells, lymphocytes, and macrophages playing important but less prominent roles. In COPD the cellular composition of the airway inflammatory infiltrate differs, with neutrophils, macrophages, and lymphocytes assuming prominence and the eosinophil playing a minor role, except in the setting of exacerbations. The contrasting inflammatory phenotypes of asthma and COPD have important implications for clinical and physiologic manifestations of disease, as well as for therapy.