Clinical significance of epithelial peptide antibiotics

Although the epithelium of macro-organisms is constantly exposed to microbial threats, infections are rather rare. Antimicrobial substances produced by epithelial cells may explain the high natural resistance of the exposed epithelia. Gene-encoded antimicrobial peptides that are believed to kill micro-organisms via pore formation have been found in the surface cells and secretions of plants and insects, and in the skin of frogs. The tongues and lungs of cattle are usually free of infection, and the first mammal-derived epithelial antimicrobial peptides, which belong to the so-called beta-defensin family, were discovered in bovine trachea and tongue. These beta-defensins are induced by infections and inflammatory agents, and are upregulated in specific anatomical sites of the epithelia, where infections occur. Recent studies have revealed that human epithelia also express beta-defensins: the tissues of the urogenital tract constitutively express human beta-defensin-1 (HBD-1), and a second human beta-defensin, HBD-2, is produced in skin and lung upon stimulation of epithelial cells with infectious or inflammatory agents. This brief review summarises our current knowledge about epithelial antimicrobial peptides, and discusses their possible role and relevance in the clinic. This includes the possibility of defective production in patients with recurrent infections, the therapeutic use of synthetic antimicrobial peptides, and the induction of their synthesis as an alternative strategy to prevent infections.