The role of epithelial beta-defensins and cathelicidins in host defense of the lung.

The continuous exposure of the epithelial surface of the conducting airways to inhaled pathogens requires the presence of an efficient innate immune system to prevent infections. The innate immune system of the lung provides protection against a broad spectrum of microbial threats through a variety of effector mechanisms. The antimicrobial peptides and proteins form important elements of this defence system in the lung. Defensins and cathelicidins are the main families of antimicrobial peptides (AMPs) that are present in airway secretions and that are expressed by the airway epithelium. Expression and release of these small (3-5 kDa) cationic peptides is regulated by exposure of epithelial cells to a wide variety of substances, including microbial products, cytokines and growth factors. More recently, also active vitamin D(3) has been implicated as a major regulator of AMPs expression. AMPs contribute to host defence through direct antimicrobial activity, as well as by modulating innate and adaptive immunity, and wound repair. Novel insight into the mechanism of action of these peptides and the regulation of their expression may lead to innovative approaches for treatment of infectious and inflammatory lung disorders.