Host Defense in Pulmonary Alveoli

,and alveolar), airway reflexes (cough and sneeze), a mucociliary escalator covering most of the airways, and specialized cell-mediated defenses (phagocytic and non-phagocytic). Lung infections (pneumonias) are frequently precipitated by the failure of one or more of these mechanisms. Nearly two decades ago Cohen & Gold discussed in the Annual Review of Physiology the mechanisms whereby pulmonary alveoli protect themselves from inhaled pathogens in the external environment (9). Because over the ensuing interval so much information has been amassed about pulmonary defenses, we have selected four areas which, in our opinion, have not received sufficient emphasis in past reviews. Those four topics are (a) the role of alveolar lining