The human cathelicidin LL-37: a multifunctional peptide involved in infection and inflammation in the lung

Antimicrobial peptides play an important role in innate immunity of the lung by acting as effector molecules in host defence against inhaled pathogens. Various families of antimicrobial peptides have been identified, including the cathelicidins. Cathelicidins are characterized by a conserved N-terminal cathelin domain and a variable C-terminal antimicrobial domain that can be released from the precursor protein after cleavage by proteinases. LL-37 is the C-terminal part of the only human cathelicidin identified to date called human cationic antimicrobial protein (hCAP-18), which is mainly expressed by neutrophils and epithelial cells. In addition to killing a broad spectrum of microorganisms, LL-37 was demonstrated to display various cellular activities related to inflammation including cytotoxicity to host cells, chemotaxis, epithelial cell activation, angiogenesis and epithelial wound repair. Focussing on this recent information, this review discusses the role of LL-37 in infection and inflammation in the lung. In addition, the importance of the fact that antimicrobial peptides such as LL-37 display a range of activities for the design and development of antimicrobial peptides for therapeutic use is discussed.