Antimicrobial peptides (AMPs) are peptides that form part of the host’s important innate immunity mechanism against pathogenic microorganisms such as Gram positive and negative bacteria, fungi and viruses.^1-2 AMPs are short peptides (<60 amino acids), exhibit a broad-spectrum antimicrobial activity at physiological conditions and are predominantly cationic.² Cathelicidins and defensins, the two extensively studied AMP families, are expressed in immune cells and at epithelial surfaces in humans.^3-5

hCAP18, human cationic antimicrobial protein, with a MW of 18 kD, is the only cathelicidin gene found in humans.¹ The N-terminus of this protein consists of a cathelin-like region (highly conserved among species) and a C-terminal termed LL-37.^6-7 An amphipathic alpha-helical peptide, LL-37 plays an important role in the first line of defense against local infection and systemic invasion of pathogens at sites of inflammation and wounds. Cytotoxic to both bacterial and normal eukaryotic cells, LL-37 is significantly resistant to proteolytic degradation in solution.^8-9 In addition to having antimicrobial activity, LL-37 has been shown to play a role in chemoattraction, dendritic cell differentiation, mast cell degranulation, cytokine secretion, angiogenesis stimulation, and wound healing.¹⁰ In other species, the C-terminal antimicrobial region varies in sizes, sequences and structures.¹⁰

The defensins are a large family of small, cationic, cysteine- and arginine-rich antimicrobial peptides. They are divided into five groups according to the spacing pattern of cysteines: plant, invertebrate, α-, β-, and θ-defensins. The latter three are mostly found in mammals. α-defensins are proteins found in neutrophils and intestinal epithelia. Human neutrophil peptides (HNP) 1-3 are microbicidal and cytotoxic defensins derived from a 94-amino acid prepro HNP1-94, co-translationally proteolyzed to proHNP20-94, then converted by removal of the anionic propiece to mature HNP65-94 (HNP-1 and -3) and HNP66-94 (HNP-2). HNP 1-4 comprise up to approximately 5% of the total cellular protein of neutrophils.^11-13

References
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