Inflammation in COPD

It is generally acknowledged that chronic inflammation plays a central role in COPD. Typically, patients show chronic inflammation of the airways, lung tissue and pulmonary blood vessels from the start of the disease.¹ The abnormal inflammatory response in COPD is triggered by the inhalation of noxious substances such as cigarette smoke and leads to structural changes and narrowing of the small airways. Inflammation is further amplified by oxidative stress.² The destruction of lung parenchyma by inflammatory cells leads to a reduced ability of the airways to remain open during expiration. It has also been shown that increased airway inflammation in the stable state is associated with frequent COPD exacerbations.²

Figure 1: Airway inflammation is present at all stages of COPD.¹
Adapted from Hogg 2004 ¹ 

Chronic COPD inflammation is very different to asthma inflammation

As our understanding of the nature of COPD inflammation has evolved, it has been recognised that it is characterised by a specific pattern of inflammation. Although both asthma and COPD are associated with an underlying chronic inflammation of the airways, there are important differences with regard to the inflammatory cells and mediators involved. The key inflammatory cells in COPD are macrophages, CD8⁺ T-lymphocytes and neutrophils. Macrophages are strongly increased in airway lumen, lung parenchyma and bronchoalveolar lavage fluid. In the airway wall and lung parenchyma an increased ratio of CD8⁺/CD4⁺ T-lymphocytes is found. Neutrophils are increased in sputum and their number grows with the progression of the disease.²

These differences in the inflammatory pattern may also account for the differences in the response to therapy achieved in the two diseases, e.g. COPD typically shows a limited response to inhaled corticosteroids as compared to the efficacy achieved in asthma.

Expert opinion

References

1. Hogg JC, Chu F, Utokaparch S, et al. The nature of small-airway obstruction in chronic obstructive pulmonary disease. N Engl J Med 2004;350: 2645-2653.
2. Global Initiative for chronic obstructive lung disease: Global strategy for the diagnosis, management, and prevention of COPD. 2011. www.goldcopd.org