Polymorphonuclear neutrophils: an effective antimicrobial force

The production and deployment of polymorphonuclear neutrophils (PMNs) are under close regulation. PMNs interact through cytokines with a number of cell types, including macrophages, lymphocytes, and endothelial cells. PMNs are guided by bacterial products and cytokines to target sites, where microbes are recognized and killed. Killing occurs through oxygen-dependent and oxygen-independent mechanisms. The frequent and se-vere infections seen in patients with defects (either congenital or acquired) in PMN func-tion demonstrate the importance of PMNs in host defense against infection. PMNs are potent inflammatory cells and can exacerbate disease states such as myocardial ischemia, gram-negative bacterial sepsis, and the adult respiratory distress syndrome. Phagocytic cells are an essential arm of host defense against microbes. The professional phagocytes in-clude monocytes, macrophages, eosinophils, and polymorphonuclear neutrophils (PMNs). PMNs ef-ficiently engulf a wide variety of microbes. Once in-gested, the invading pathogens are killed by oxygen-dependent and oxygen-independent mechanisms. In this review we will summarize the present under-standing of PMN function and provide an update of new developments concerning the role of PMNs in health and disease. Origin, Development, and Deployment PMNs originate from pluripotent stem cells in the bone marrow [1-3]. Granulocytes begin as myelo-blasts, which differentiate by division into myelo-cytes, Subsequently, during a 7-day postmitotic pe-riod, cytoplasmic and nuclear changes occur that result in a fully mature and functional PMN. The PMN acquires two major populations of granules during development. The primary (azurophilic) gran-ules appear during the mitotic period and contain myeloperoxidase, acid hydrolases, lysozyme, cationic proteins, and neutral proteases- including elastase. Primary granules are released into the phagosome following phagocytosis and provide the PMN with localized microbicidal activity. The secondary (spe