Innate immunity and pulmonary host defense

The lung, in order to facilitate gas exchange, represents the largest epith elial surface area of the body in contact with the external environment. As normal respiration occurs, the upper and lower airways are repeatedly expo sed to a multitude of airborne particles and microorganisms. Since these ag ents are frequently deposited on the surface of the respiratory tract, an e laborate system of defense mechanisms is in place to maintain the sterility of the lung. Innate defenses are primarily responsible for the elimination of bacterial organisms from the alveolus. Early bacterial clearance is med iated by a dual phagocytic system involving both alveolar macrophages and p olymorphonuclear leukocytes. The recruitment and activation of inflammatory cells at a site of infection involves the orchestrated expression of leuko cyte and vascular adhesion molecules, as well as the establishment of chemo tactic gradients via the generation of proinflammatory cytokines and chemok ines. Immunologic manipulation of innate immunity may serve as an important adjuvant therapy in the treatment of both immunocompromised and immunocomp etent patients with severe lung infections. As the complexities of the host -pathogen interaction are further dissected and elucidated it is likely tha t the therapeutic benefits from these approaches will be realized.