Defensins: Antimicrobial Peptides of Innate Immunity

Defensins are one of the largest and most studied families of antimicrobial peptides. Defensins are a family of small, variably cationic proteins which are highly abundant in the granules of mammalian phagocytes. The members of this family are variably arginine-rich and all share 6 conserved cysteine residues that participate in intramolecular disulfide bonds. The peptides were first detected in rabbit and guinea-pig neutrophils. Some defensins are broadly antimicrobial, antiviral, and cytotoxic, while others are chemotactic, opsonic, or may modulate hormonal responses. Alpha- and beta-defensins have a similar three-dimensional structure and antimicrobial activity but they differ markedly in the location of the intra-molecular disulphide bridges, structure of their precursors and sites of expression. Due to their activity against bacteria, viruses, and fungi, antimicrobial peptides are important factors in the innate resistance system of humans and animals. They are called “new generation antibiotics” for their potential use in preventive and therapeutic medicine.