DEFENSE-MECHANISMS OF RESPIRATORY MEMBRANE

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Abstract
The success or failure of pulmonary defense mechanisms largely determines the appearance of clinical lung disease [human]. The lung is protected by interlocking systems of nonspecific and specific defenses. Inhaled substances can be isolated by mechanical barriers or can be physically removed from the lung either by transport up the bronchial mucociliary escalator or by transport through interstitial and lymphatic channels leading to lymph nodes. Substances can be locally detoxified within the lung by interaction with secretory proteins, such as antibodies, or by neutralization and dissolution within phagocytic cells. The pulmonary alevolar macrophage is the central figure in the protection of the respiratory membrane, operating in all 3 of the nonspecific modes of defense and augmented by specific immunologic mechanisms as well. Alteration in macrophage function and physiology may be crucial in determining the effectiveness of pulmonary defense. Functioning as resident defender of the alveolus, the macrophage is an important effector of the pulmonary immune response and plays a key role in the pathogenesis of a wide variety of inflammatory, destructive and fibrotic lung diseases. Humoral and cell-mediated immune responses amplify and direct lung defenses against infection and may also participate in protection against other agents. Immunoglobulin [Ig] A and IgG, microbial neutralizing and opsonizing antibodies, and macrophage-stimulating T [thymus derived] lymphocytes are the major immunospecific forms of lung defense. Infectious agents, cigarette smoke, air pollutants, industrial dusts and a spectrum of coexistent disease states may impair pulmonary defense mechanisms and increase susceptibility to acute and chronic respiratory diseases.