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...

Background: Neonatal neutrophil dysfunction contributes to inflammatory tissue damage in newborn infants. Toll-like receptors (TLRs) activate the innate immune response through recognition of pathogen-associated molecular patterns. Expression and function of TLRs by neonatal neutrophils has not well been characterized. Objective: We hypothesized that, compared to polymorphonuclear leukocytes (PMNs) isolated from adults, neonatal PMNs isolated from either term or preterm infants express and release different levels of inflammatory cytokines and chemokines in response to stimulation with TLR1–9 agonists. Methods: We stimulated PMNs isolated from preterm (n = 12) and term (n = 10) infants as well as adults (n = 10) with agonists recognized by TLRs1–9 and quantified chemokine and cytokine expression and secretion by ELISA and Luminex® multiplex quantification assay. Results: Neonatal and adult PMNs stimulated with agonists recognized by TLRs1–9 differentially secrete inflammatory products. Signaling via TLR2 heterodimers is a potent mechanism for release of interleukin-8, a critical proinflammatory chemokine, by neonatal PMNs – a previously unrecognized facet of neonatal inflammation. Following TLR1/2 (PAM3CSK4) stimulation, interleukin-8 secretion by neonatal PMNs, whether term or preterm, substantially exceeds that of adult PMNs assayed in parallel. Conclusions: These studies provide new insights relevant to the inflammatory biology of neonates, both term and preterm, and implicate exaggerated PMN recruitment in neonatal syndromes of dysregulated inflammation such as necrotizing enterocolitis or neonatal chronic lung disease.

No abstract