[Physiologic and pathophysiologic significance of antimicrobial (host defensive) small peptides]

Antimicrobial peptides are typically small cationic and amphiphilic molecules, which exhibit a wide spectrum of antimicrobial activity. These peptides are seen as an important and ancient mechanism of defence for most living organisms. Some of these peptides are produced constitutively whereas others are induced by exogenous microbial products or by proinflammatory cytokines. The antimicrobial peptides differ widely in their biochemical properties, but typically they act directly against microbes through a mechanism involving membrane disruption and pore formation leading to leakage of cell content and cell death. In human beings the defensins, cathelicidins and histatins are the principal antimicrobial peptides. They are found in neutrophils, in some other white blood cells and in the epithelium of every major organ system examined. Recent studies revealed that, beyond antimicrobial activity, the antimicrobial peptides are involved in a remarkably broad range of host defence related functions including neutralisation of some bacterial toxins and augmentation of both innate and adaptive immune mechanisms. Since several of them have proved to be effective against antibiotic resistant bacteria, these peptides are being widely used as blueprints for the design of new antimicrobial agents.