Pulmonary surfactant: a front line of lung host defense

The lung is a uniquely vulnerable organ. Residing at the interface of the body and the environment, the lung is optimized for gas exchange, having a very thin, delicate epithelium, abundant blood flow, and a vast surface area. Inherent in this structure is an enormous immunological burden from pathogens, allergens, and pollutants resident in the 11,000 liters of air inhaled daily. Fortunately, protective immune mechanisms act locally in the lung to facilitate clearance of inhaled pathogens and to modulate inflammatory responses. These defensive mechanisms include both innate (nonantibody-mediated) and adaptive (antibody-mediated) systems. The purpose of this commentary is to review briefly the functions of one unique lung innate immune system, pulmonary surfactant, and to highlight the recent findings of Wu et al. (1) described in this issue of the JCI. Wu and colleagues report a new and intriguing innate immune function of surfactant: direct antimicrobial activity.