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Blood, 18 June 2009, Vol. 113, No. 25, pp. 6419-6427. Prepublished online as a Blood First Edition Paper on February 12, 2009; DOI 10.1182/blood-2008-07-171629.
PHAGOCYTES, GRANULOCYTES, AND MYELOPOIESIS Impaired neutrophil extracellular trap (NET) formation: a novel innate immune deficiency of human neonates1 Department of Pediatrics/Neonatology, 2 Program in Human Molecular Biology and Genetics, 3 Department of Internal Medicine, 4 Electron Microscopy Core Research Facility, 5 Cell Imaging/Fluorescence Microscopy Core Research Facility, and 6 Department of Pathology, University of Utah, Salt Lake City 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. The deficiency in NET formation is paralleled by a previously unrecognized deficit in extracellular bacterial killing. Generation of ROSs did not complement the defect in NET formation by neonatal neutrophils, as it did in adult cells with inactivated NADPH oxidase, demonstrating that ROSs are necessary but not sufficient signaling intermediaries and identifying a deficiency in linked or downstream pathways in neonatal leukocytes. Impaired NET formation may be a critical facet of a common developmental immunodeficiency that predisposes newborn infants to infection.
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