New concepts in the pathobiology of chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is characterized by an abnormal persistent inflammatory response to cigarette smoke. This noxious insult leads to emphysema and airway remodeling, manifested by squamous and mucous metaplasia of the epithelium, smooth muscle hypertrophy, and airway wall fibrosis. These pathologic abnormalities interact synergistically to cause progressive airflow obstruction. Although it has been accepted that the spectrum of COPD is vast, the reasons for the development of different phenotypes from the same exposure to cigarette smoke have not been determined. Furthermore, it is becoming increasingly clear that airways disease and emphysema often coexist in many patients, even with a clear clinical phenotype of either emphysema or chronic bronchitis. Recent studies have focused on the nature of the inflammatory response to cigarette smoke, the inflammatory cell lines responsible for COPD pathogenesis, and new biomarkers for disease activity and progression. New cytokines are being discovered, and the complex interactions among them are being unraveled. The inflammatory biomarker that has received the most attention is C-reactive protein, but new ones that have caught our attention are interleukin (IL)-6, tumor necrosis factor-alpha, IL-8, and IL-10. Further research should focus on how these new concepts in lung inflammation interact to cause the various aspects of COPD pathology.