Role of antimicrobial peptides in human innate defense against bacteria

Abstract

Antimicrobial peptides (AMPs) are important components of the innate immune system of many vertebrate and invertebrate species. These small peptides directly kill microorganisms by inducing microbial cell death. This review focuses on the mechanisms of direct antimicrobial effects against Gram positive and Gram negative bacteria of the main human AMPs, α-defensins, β-defensins, the cathelicidin LL-37 and the histatins. Effectiveness of the AMPs is dependent on both the properties of the AMPs and the target microbe. The size, cationic charge and amphipathicity allows AMPs to target and disrupt the membrane integrity of several bacteria. Different mechanisms of lipid bilayer disruption by AMPs are described by the ‘barrel-stave’, the ‘toroidal-pore’ and the ‘carpet’ model. Although these models are generally accepted to clarify direct antimicrobial killing by AMPs, the precise mechanisms of the main human AMPs remains to be clarified. In addition, the microbicidal activity of some AMPs might be explained by other mechanisms.