Antibiotic peptides and serine protease homologs in human polymorphonuclear leukocytes: defensins and azurocidin.

The azurophil granule, a specialized lysosome of neutrophils, contains two families of antimicrobial proteins, each with four members. They are the defensins, comprising human neutrophil protein 1, -2, -3 and -4, on the one hand and the serprocidins, comprising cathepsin G, elastase, proteinase 3 and azurocidin, on the other. Defensins appear to contribute to mammalian as well as invertebrate immunity. Recent studies show that defensins and structurally related peptides are found not only in phagocytes but also in intestinal and respiratory cells. Aside from their antibiotic function, members of the defensin family may also act as hormonal agents. Within the serprocidin family the genes encoding the novel antibiotics and serine protease homologs azurocidin and proteinase 3 have been identified recently.