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COPD is characterised functionally by a persistent airflow limitation, which is not fully reversible and is usually progressive. The pathological hallmarks of COPD are, on the one hand chronic inflammation and remodelling of the small airways (ie, bronchiolitis) and, on the other hand enlargement of alveolar spaces due to destruction of alveolar lung tissue (ie, emphysema).1 Fibrosis of the small airways and loss of elastic recoil due to emphysematous destruction contribute to chronic airflow limitation in COPD. Elastic fibres, principal components of the extracellular matrix (ECM) of alveolar septa, provide mechanical elasticity to the lungs and interconnect the lung parenchyma with small airways via alveolar attachments. An imbalance between proteases (such as neutrophil elastase) and antiproteases (such as α1-antitrypsin, the main inhibitor of neutrophil elastase), leading to a net increase in proteolytic activity, has been implicated in the pathophysiology of COPD.2 However, two opposing processes are supposed to drive the pathogenesis of small airway fibrosis and emphysema: the thickening of the small airway walls results from an exaggerated repair process leading to a marked increase in deposition of ECM, whereas the emphysematous destruction of the lung tissue is indicative of an insufficiënt production of ECM and, thus, a defective repair. Since small airway fibrosis and emphysema occur in close proximity to each other in COPD, the underlying mechanisms of their pathogenesis remain enigmatic. …
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