Breaching Host Defenses in the Normal Respiratory Tract

The lung is a highlyvulnerableorgan,open to attack from a variety of airborn agents: toxic gases, particles, aerosolized liquids, viruses, and bacteria. An impressive array of defense mechanisms thus stand guard to repel the invaders before they gain a beachhead. These defense mechanisms are ingenious and remarkably efficient, but they may be overcome even in the normal host. When this occurs, the lung itself is threatened and the systemic defenses of the body “scramble,” like a division of the Strategic Air Command, to reinforce the local troops. The analogy to warfare may be melodramatic, but it is apt to describe the manner in which the respiratory tract repels continual assaults on its integrity.