Chronic bronchitis: the role of viruses.

Mucus is produced by the epithelial cells in the glands, gland ducts, and the cells lining the airway lumen in the lower airways. The chronic cough and sputum production that defines chronic bronchitis is associated with an inflammatory reaction involving this mucussecreting apparatus. Respiratory viral infections target the epithelial cells of the lung producing desquamation, microvascular dilatation, edema, and an inflammatory cell infiltrate. These changes predispose the lower airways to bacterial infection by interfering with mucociliary clearance and reducing bacterial killing by macrophages. The exact role of those infections in the pathogenesis of chronic bronchitis has not been clearly determined but they probably play a critical role in inducing bacterial colonization and initiating acute exacerbations of COPD. This article reviews the classification of the viral agents responsible for respiratory tract infection and the nature of the changes they produce in the normal airways and in the airways of patients with chronic bronchitis during acute infections.