Antimicrobial peptides are endogenous antibiotics.
They have been isolated from diverse species throughout the plant and animal kingdoms and are thought to represent an evolutionary very old mechanism of host defense. These peptides characteristically have a broad-spectrum of antimicrobial activity, including bacteria, fungi and certain viruses. Their antimicrobial activity is attributed to their ability to selectively disrupt microbial membrane functions at micromolar concentrations. Additional biological activities of many antimicrobial peptides are a result of high affinity interactions with various cell surface receptors. Defensins are the major class of antimicrobial peptides in mammals, and 8 defensins have been identified in humans to date.