Neutrophils are highly specialized innate effector cells that have evolved for killing of pathogens. Human neonates have a common multifactorial syndrome of neutrophil dysfunction that is incompletely characterized and contributes to sepsis and other severe infectious complications. We identified a novel defect in the antibacterial defenses of neonates: inability to form neutrophil extracellular traps (NETs). NETs are lattices of extracellular DNA, chromatin, and antibacterial proteins that mediate extracellular killing of microorganisms and are thought to form via a unique death pathway signaled by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-generated reactive oxygen species (ROS). We found that neutrophils from term and preterm infants fail to form NETs when activated by inflammatory agonists-in contrast to leukocytes from healthy adults. IntroductionPolymorphonuclear leukocytes (PMNs, neutrophils) are highly specialized cellular effectors in host defense and immune surveillance. Mature human PMNs from healthy adults have a unique repertoire of activities, including phagocytosis, degranulation of antimicrobial enzymes and peptides, and generation of oxygen radicals with antimicrobial properties. 1-6 Synthesis of inflammatory and regulatory lipids and proteins complements these innate mechanisms. 1,4,5 PMNs have evolved for capture, containment, and destruction of bacteria and fungi and also have activity against intracellular pathogens and viruses. 2,3 PMNs have additional important roles in tissue repair and integration of innate and adaptive immune responses. 6 If, however, these specialized defensive mechanisms become dysregulated or unregulated, PMNs can paradoxically be mediators of inflammatory tissue injury. 1,6 Consistent with their requisite activities in host defense, defects in PMN functions cause immune deficiency syndromes. 2,7 Neutrophil defects can be hereditary, developmental, or acquired in nature. Specific genetic deficiencies in PMN function cause significant morbidity in subsets of children and adults and, in parallel, provide unique insights into molecular mechanisms that regulate leukocyte activities. 7,8 Nevertheless, these disorders are rare and arcane. In contrast, the developmental syndrome of neonatal neutrophil dysfunction, which is particularly important in premature infants, is common and contributes to infections in infants worldwide. As an example, neonatal PMN dysfunction is thought to be a pivotal feature of sepsis in the newborn. 9-11 The incidence of neonatal sepsis is estimated to be 1 to 5 cases per 1000 live births in the United States and to be even higher after very low birth weight premature deliveries (15-19/1000); in contrast, the incidence of sepsis is much lower in children older than 1 year of age and in young adults. 12-15 Furthermore, the incidence of neonatal sepsis is as high as 25% in some areas of the developing world. 16,17 Thus, neonatal PMN dysfunction is a contributor to a public health problem of significant proportions, and also may pr...

Neutrophils are highly specialized innate immune effector cells that evolved for antimicrobial host defense. In response to inflammatory stimuli and pathogens, they form neutrophil extracellular traps (NETs), which capture and kill extracellular microbes. Deficient NET formation predisposes humans to severe infection, but, paradoxically, dysregulated NET formation contributes to inflammatory vascular injury and tissue damage. The molecular pathways and signaling mechanisms that control NET formation remain largely uncharacterized. Using primary human neutrophils and genetically manipulated myeloid leukocytes differentiated to surrogate neutrophils, we found that mammalian target of rapamycin ( IntroductionNeutrophils (polymorphonuclear leukocytes, PMNs) are key effector cells in infection, inflammation, and tissue injury. 1 Formation of neutrophil extracellular traps (NETs), first identified with human PMNs, is a function of neutrophils. 2 NETs are complex lattices of decondensed chromatin that trap and kill bacteria, fungi, and some parasites by exposing them to high concentrations of NETassociated microbicidal factors. 3,4 Rapidly evolving studies indicate that NETs effect extracellular microbial killing while limiting the spread of pathogens in vivo. 3,5 The intracellular signaling pathways that regulate NET formation by PMNs remain largely unknown. There is evidence that generation of reactive oxygen species (ROS) is a key event. 4,6 Nevertheless, we showed in primary human PMNs that NET formation requires signaling events and regulatory pathways in addition to ROS generation. 4 Consistent with our results, subsequent studies in human HL-60 myeloid leukocytes and genetically altered mice indicate that activity of peptidylarginine deiminase 4, an enzyme responsible for chromatin decondensation, is also required. 5,7 Recent observations further suggest that NET formation requires enzymatic activity of neutrophil elastase (NE) and myeloperoxidase to initiate degradation of core histones that lead to chromatin decondensation before plasma membrane rupture. 8 Furthermore, ROS generation and NET formation can be dissociated under some conditions. 9,10 Thus, molecular regulation of NET formation is complex and may involve multiple signaling pathways and effector events, depending on the neutrophil agonists and inflammatory context.The mammalian target of rapamycin (mTOR) is a highly conserved PI3K-like serine/threonine kinase with functional homologs found in all studied eukaryotic organisms. 11 mTOR integrates nutrient, energy, oxygen sensing, and mitogenic input signals. 12 We found that mTOR also responds to inflammatory signals and mediates a previously unrecognized pathway of posttranscriptional gene regulation in human PMNs. 13 These results identified a new mechanism by which mTOR can regulate innate, as well as, adaptive, immune responses. Immunoregulatory activities of mTOR are now increasingly recognized. 14 Recent observations indicate that hypoxia inducible factor 1␣ (HIF-1␣), the regulated subunit of ...