Cytokines in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by chronic obstruction of expiratory flow affecting peripheral airways, associated with chronic bronchitis (mucus hypersecretion with goblet cell and submucosal gland hyperplasia) and emphysema (destruction of airway parenchyma), together with fibrosis and tissue damage, and inflammation of the small airways. Cytokines are extracellular signalling proteins. Increased levels of interleukin (IL)-6, IL-1beta, tumour necrosis factor-alpha (TNF-alpha) and IL-8 have been measured in sputum, with further increases during exacerbations, and the bronchiolar epithelium over-expresses monocyte chemotactic protein (MCP)-1 and IL-8. IL-8 can account for some chemotactic activity of sputum, and sputum IL-8 levels correlate with airway bacterial load and blood myeloperoxidase levels. The expression of chemokines such as regulated on activation, normal T-cell expressed and secreted (RANTES) may underlie the airway eosinophilia observed in some COPD patients. Cytokines may be involved in tissue remodelling. TNF-alpha and IL-1beta stimulate macrophages to produced matrix metalloproteinase-9 (MMP-9), and bronchial epithelial cells to produce extracellular matrix glycoproteins such as tenascin. Increased expression of transforming growth factor-beta (TGFbeta) and of epidermal growth factor (EGF) occurs in the epithelium and submucosal cells of patients with chronic bronchitis. TGFbeta and EGF activate proliferation of fibroblasts, while activation of the EGF receptor leads to mucin gene expression. The cytokine profile seen in chronic obstructive pulmonary disease is different from that observed in asthma. The role of these cytokines needs to be defined and there is a potential for anticytokine therapy in chronic obstructive pulmonary disease.