Proteolysis in the lung.

Pulmonary emphysema is a major component of the morbidity and mortality of chronic obstructive pulmonary disease (COPD), a condition that has become the fourth leading cause of death in the USA, and is becoming epidemic worldwide. Emphysema is defined as enlargement of peripheral airspaces of the lung including respiratory bronchioles, alveolar ducts and alveoli, accompanied by destruction of the walls of these structures. The pathogenesis of emphysema can be dissected into three interrelated events: 1) chronic exposure to cigarette smoke may lead to inflammatory cell recruitment within the terminal airspaces of the lung; 2) these inflammatory cells release elastolytic proteinases that damage the extracellular matrix of the lung; and 3) ineffective repair of elastin and perhaps other extracellular matrix components result in pulmonary emphysema.