Role for IRAK-4 and p38 in Neutrophil Signaling in Response to Bacterial Lipoproteins from Staphylococcus aureus.

Neutrophils, polymorphonuclear leukocytes (PMN), express numerous pattern recognition receptors, including TLRs, capable of recognizing a wide variety of pathogens. Receptor engagement initiates a cascade of PMN responses with some occurring in seconds, and some requiring de novo protein synthesis over the course of many hours. Although numerous species of bacteria and bacterial products have been shown to activate PMN via TLRs, the signaling intermediates required for distinct PMN responses have not been well-defined in human PMN. Given the potential for host tissue damage by overexuberant PMN activity, a better understanding of neutrophil signaling is needed to generate effective therapies. We hypothesized that PMN responses to a lipoprotein-containing cell membrane preparation from methicillin-resistant S. aureus (MRSA-CMP) would activate signaling via IRAK4 and p38, with potentially distinct pathways for early vs. late responses. Using human PMN we investigated MRSA-CMP-elicited reactive oxygen species (ROS) production, elastase activity, NET formation, IL-8 production, and the role of IRAK4 and p38 activation. MRSA-CMP elicited ROS in a concentration and lipoprotein-dependent manner. MRSA-CMP elicited phosphorylation of p38 MAPK, and MRSA-CMP-elicited ROS production was partially dependent on p38 MAPK and IRAK4 activation. Inhibition of IRAK4 resulted in a reduction of p38 phosphorylation. MRSA-CMP-elicited elastase activity and NET formation was partially dependent on p38 MAPK activation, but independent of IRAK4 activation. MRSA-CMP-elicited IL-8 production required both p38 and IRAK4 activation. In conclusion, MRSA-CMP elicits PMN responses via distinct signaling pathways. There is potential to target components of the neutrophil inflammatory response without compromising critical pathogen-specific immune functions.

Granular Insights: Neutrophil Predominance and Elastase Release in Severe Asthma Exacerbations in a Pediatric Cohort.

The chronic inflammatory component of asthma is propagated by granulocytes, including neutrophils and eosinophils, in the peripheral circulation and airway. Previous studies have suggested that these cells have an altered expression of adhesion-related molecules and a propensity for the release of granule contents that may contribute to tissue damage and enhance inflammatory complications in patients with status asthmaticus. The goal of this prospective cohort study at a tertiary care pediatric hospital with a large population of asthma patients was to assess the role of granulocyte-based inflammation in the development of asthma exacerbation. Subjects were enrolled from two patient populations: those with mild-to-moderate asthma exacerbations seen in the emergency department and those with severe asthma admitted to the intensive care unit (PICU). Clinical data were collected, and blood was drawn. Granulocytes were immediately purified, and the phenotype was assessed, including the expression of cell surface markers, elastase release, and cytokine production. Severe asthmatics admitted to the PICU displayed a significantly higher total neutrophil count when compared with healthy donors. Moreover, little to no eosinophils were found in granulocyte preparations from severe asthmatics. Circulating neutrophils from severe asthmatics admitted to the PICU displayed significantly increased elastase release ex vivo when compared with the PMN from healthy donors. These data suggest that the neutrophil-based activation and release of inflammatory products displayed by severe asthmatics may contribute to the propagation of asthma exacerbations.

Quantifying neutrophil extracellular trap release in a combined infection-inflammation NET-array device.

Excessive release of neutrophil extracellular traps (NETs) has been reported in various human pathologies, including COVID-19 patients. Elevated NET levels serve as a biomarker, indicating increased coagulopathy and immunothrombosis risks in these patients. Traditional immunoassays employed to quantify NET release focus on bulk measurements of released chromatin in simplified microenvironments. In this study, we fabricated a novel NET-array device to quantify NET release from primary human neutrophils with single-cell resolution in the presence of the motile bacteria Pseudomonas aeruginosa PAO1 and inflammatory mediators. The device was engineered to have wide chambers and constricted loops to measure NET release in variably confined spaces. Our open NET-array device enabled immunofluorescent labeling of citrullinated histone H3, a NET release marker. We took time-lapse images of primary healthy human neutrophils releasing NETs in clinically relevant infection and inflammation-rich microenvironments. We then developed a computer-vision-based image processing method to automate the quantification of individual NETs. We showed a significant increase in NET release to Pseudomonas aeruginosa PAO1 when challenged with inflammatory mediators tumor necrosis factor-α [20 ng mL-1] and interleukin-6 [50 ng mL-1], but not leukotriene B4 [20 nM], compared to the infection alone. We also quantified the temporal dynamics of NET release and differences in the relative areas of NETs, showing a high percentage of variable size NET release with combined PAO1 - inflammatory mediator treatment, in the device chambers. Importantly, we demonstrated reduced NET release in the confined loops of our combined infection-inflammation microsystem. Ultimately, our NET-array device stands as a valuable tool, facilitating experiments that enhance our comprehension of the spatiotemporal dynamics of NET release in response to infection within a defined microenvironment. In the future, our system can be used for high throughput and cost-effective screening of novel immunotherapies on human neutrophils in view of the importance of fine-tuning NET release in controlling pathological neutrophil-driven inflammation.

Itaconate-producing neutrophils regulate local and systemic inflammation following trauma.

Modulation of the immune response to initiate and halt the inflammatory process occurs both at the site of injury as well as systemically. Due to the evolving role of cellular metabolism in regulating cell fate and function, tendon injuries that undergo normal and aberrant repair were evaluated by metabolic profiling to determine its impact on healing outcomes. Metabolomics revealed an increasing abundance of the immunomodulatory metabolite itaconate within the injury site. Subsequent single-cell RNA-Seq and molecular and metabolomic validation identified a highly mature neutrophil subtype, not macrophages, as the primary producers of itaconate following trauma. These mature itaconate-producing neutrophils were highly inflammatory, producing cytokines that promote local injury fibrosis before cycling back to the bone marrow. In the bone marrow, itaconate was shown to alter hematopoiesis, skewing progenitor cells down myeloid lineages, thereby regulating systemic inflammation. Therapeutically, exogenous itaconate was found to reduce injury-site inflammation, promoting tenogenic differentiation and impairing aberrant vascularization with disease-ameliorating effects. These results present an intriguing role for cycling neutrophils as a sensor of inflammation induced by injury - potentially regulating immune cell production in the bone marrow through delivery of endogenously produced itaconate - and demonstrate a therapeutic potential for exogenous itaconate following tendon injury.

Neutrophil metabolomics in severe COVID-19 reveal GAPDH as a suppressor of neutrophil extracellular trap formation.

Severe COVID-19 is characterized by an increase in the number and changes in the function of innate immune cells including neutrophils. However, it is not known how the metabolome of immune cells changes in patients with COVID-19. To address these questions, we analyzed the metabolome of neutrophils from patients with severe or mild COVID-19 and healthy controls. We identified widespread dysregulation of neutrophil metabolism with disease progression including in amino acid, redox, and central carbon metabolism. Metabolic changes in neutrophils from patients with severe COVID-19 were consistent with reduced activity of the glycolytic enzyme GAPDH. Inhibition of GAPDH blocked glycolysis and promoted pentose phosphate pathway activity but blunted the neutrophil respiratory burst. Inhibition of GAPDH was sufficient to cause neutrophil extracellular trap (NET) formation which required neutrophil elastase activity. GAPDH inhibition increased neutrophil pH, and blocking this increase prevented cell death and NET formation. These findings indicate that neutrophils in severe COVID-19 have an aberrant metabolism which can contribute to their dysfunction. Our work also shows that NET formation, a pathogenic feature of many inflammatory diseases, is actively suppressed in neutrophils by a cell-intrinsic mechanism controlled by GAPDH.

Evaluation of an association between RANKL and OPG with bone disease in people with cystic fibrosis.

BACKGROUND: As people with Cystic Fibrosis (CF) live longer, extra-pulmonary complications such as CF-related bone disease (CFBD) are becoming increasingly important. The etiology of CFBD is poorly understood but is likely multifactorial. Bones undergo continuous remodeling via pathways including RANK (receptor activator of NF-κB)/sRANKL (soluble ligand)/OPG (osteoprotegerin). We sought to examine the association between sRANKL (stimulant of osteoclastogenesis) and OPG levels (inhibitor of osteoclast formation) and CFBD to investigate their potential utility as biomarkers of bone turnover in people with CF. METHODS: We evaluated sRANKL and OPG in plasma from people with CF and healthy controls (HC) and compared levels in those with CF to bone mineral density results. We used univariable and multivariable analysis to account for factors that may impact sRANKL and OPG. RESULTS: We found a higher median [IQR] sRANKL 10,896pg/mL [5,781-24,243] CF; 2,406pg.mL [659.50-5,042] HC; p= 0.0009), lower OPG 56.68pg/mL [36.28-124.70] CF; 583.20pg/mL [421.30-675.10] HC; p < 0.0001), and higher RANKL/OPG in people with CF no BD than in HC (p < 0.0001). Furthermore, we found a higher RANKL/OPG ratio 407.50pg/mL [214.40-602.60] CFBD; 177.70pg/mL [131.50-239.70] CF no BD; p = 0.007) in people with CFBD versus CF without bone disease. This difference persisted after adjusting for variables thought to impact bone health. CONCLUSIONS: The current screening recommendations of imaging for CFBD may miss important markers of bone turnover such as the RANKL/OPG ratio. These findings support the investigation of therapies that modulate the RANK/RANKL/OPG pathway as potential therapeutic targets for bone disease in CF.

Novel neutrophil phenotypic signature in pediatric patients with type 1 diabetes and diabetic ketoacidosis.

Type 1 diabetes (T1D) is a chronic inflammatory condition sometimes complicated by acute diabetic ketoacidosis (DKA). A subset of patients with T1D develop DKA independent of known risk factors. This study tested the hypothesis that circulating polymorphonuclear leukocytes (PMN) from children with T1D and DKA would exhibit a primed phenotype and that the signature would be unique in patients predisposed to have DKA. Using a prospective cohort study design, neutrophil phenotype was assessed in 30 patients with T1D seen in endocrinology clinic for routine care, 30 patients with acute DKA, and 36 healthy donors. Circulating PMN from patients with DKA display a primed phenotype with increased basal cell-surface CD11b, L-selectin shedding, and enhanced fMLF-elicited reactive oxygen species (ROS) production. Moreover, PMN from T1D patients both with and without DKA lack the capacity to be further primed by incubation with TNF-α, a classic priming stimulus. Primed PMN phenotypic signatures demonstrated are independent of hemoglobin A1c, the premier biological marker for DKA risk, and are consistent with a hyperinflammatory state. A single nucleotide polymorphism in TLR-1 (1805G>T), known to be associated with a hyperinflammatory PMN phenotype, correlated with DKA. This study elucidated a novel phenotypic signature in circulating PMN from children with T1D with and without DKA, and suggests the possibility of a previously unrecognized PMN phenotype with potential clinical implications. Immunophenotype and genotype may be applicable as biomarkers for DKA risk stratification in patients with T1D.

Neutrophil Extracellular Trap Formation Potential Correlates with Lung Disease Severity in COVID-19 Patients.

Severe lung inflammation is common in life-threatening coronavirus disease 2019 (COVID-19). This study tested the hypothesis that polymorphonuclear (PMN, neutrophil) phenotype early in the course of disease progression would predict peak lung disease severity in patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is increasingly evident that PMN activation contributes to tissue injury resulting from extracellular reactive oxygen species generation, granule exocytosis with release of proteases, neutrophil extracellular trap (NET) formation, and release of cytokines. The current study focuses on PMN activation in response to SARS-CoV-2 infection, specifically, the association between NETs and lung disease. This is a prospective cohort study at an academic medical center with patients enrolled within 4 days of admission at 3 tertiary hospitals: Clements University Hospital, Parkland Memorial Hospital, and Children's Health in Dallas, TX. Patients were categorized as having minimal or moderate to severe lung disease based on peak respiratory support. Healthy donor controls matched for age, sex, race, and ethnicity were also enrolled. Neutrophils from COVID-19 patients displayed greater IL-8 expression, elastase release, and NET formation as compared with neutrophils from healthy donors. Importantly, neutrophils from COVID-19 patients had enhanced NET formation in the absence of any additional stimulus, not seen in PMN from healthy donors. Moreover, PMA-elicited NET formation by circulating PMN correlated with severity of lung disease. We speculate that neutrophil immuno-phenotyping can be used to predict lung disease severity in COVID-19 patients.

Lipoproteins from Staphylococcus aureus Drive Neutrophil Extracellular Trap Formation in a TLR2/1- and PAD-Dependent Manner.

Neutrophils, polymorphonuclear leukocytes (PMN), play a critical role in the innate immune response to Staphylococcus aureus, a pathogen that continues to be associated with significant morbidity and mortality. Neutrophil extracellular trap (NET) formation is involved in ensnaring and killing of S. aureus, but this host-pathogen interaction also leads to host tissue damage. Importantly, NET components including neutrophil proteases are under consideration as therapeutic targets in a variety of disease processes. Although S. aureus lipoproteins are recognized to activate cells via TLRs, specific mechanisms of interaction with neutrophils are poorly delineated. We hypothesized that a lipoprotein-containing cell membrane preparation from methicillin-resistant S. aureus (MRSA-CMP) would elicit PMN activation, including NET formation. We investigated MRSA-CMP-elicited NET formation, regulated elastase release, and IL-8 production in human neutrophils. We studied PMN from healthy donors with or without a common single-nucleotide polymorphism in TLR1, previously demonstrated to impact TLR2/1 signaling, and used cell membrane preparation from both wild-type methicillin-resistant S. aureus and a mutant lacking palmitoylated lipoproteins (lgt). MRSA-CMP elicited NET formation, elastase release, and IL-8 production in a lipoprotein-dependent manner. TLR2/1 signaling was involved in NET formation and IL-8 production, but not elastase release, suggesting that MRSA-CMP-elicited elastase release is not mediated by triacylated lipoproteins. MRSA-CMP also primed neutrophils for enhanced NET formation in response to a subsequent stimulus. MRSA-CMP-elicited NET formation did not require Nox2-derived reactive oxygen species and was partially dependent on the activity of peptidyl arginine deiminase (PAD). In conclusion, lipoproteins from S. aureus mediate NET formation via TLR2/1 with clear implications for patients with sepsis.

Mycobacterium tuberculosis Lipoarabinomannan Activates Human Neutrophils via a TLR2/1 Mechanism Distinct from Pam3CSK4.

Neutrophils, polymorphonuclear (PMN) leukocytes, play an important role in the early innate immune response to Mycobacterium tuberculosis infection in the lung. Interactions between PMN and mycobacterial lipids impact the activation state of these migrated cells with consequences for the surrounding tissue in terms of resolution versus ongoing inflammation. We hypothesized that lipoarabinomannan from M. tuberculosis (Mtb LAM) would prime human PMN in a TLR2-dependent manner and investigated this with specific comparison with the purified synthetic TLR2 agonists, Pam3CSK4 and FSL-1. In contrast to Pam3CSK4 and FSL-1, we found Mtb LAM did not induce any of the classical PMN priming phenotypes, including enhancement of NADPH oxidase activity, shedding of l-selectin, or mobilization of CD11b. However, exposure of PMN to Mtb LAM did elicit pro- and anti-inflammatory cytokine production and release in a TLR2/1-dependent manner, using the TLR1 single-nucleotide polymorphism rs5743618 (1805G/T) as a marker for TLR2/1 specificity. Moreover, Mtb LAM did not elicit p38 MAPK phosphorylation or endocytosis, although these processes occurred with Pam3CSK4 stimulation, and were necessary for the early priming events to occur. Interestingly, Mtb LAM did not abrogate priming responses elicited by Pam3CSK4 Notably, subfractionation of light membranes from Pam3CSK4 versus Mtb LAM-stimulated cells demonstrated differential patterns of exocytosis. In summary, Mtb LAM activates PMN via TLR2/1, resulting in the production of cytokines but does not elicit early PMN priming responses, as seen with Pam3CSK4 We speculate that the inability of Mtb LAM to prime PMN may be due to differential localization of TLR2/1 signaling.

Nox2 Regulates Platelet Activation and NET Formation in the Lung.

The mortality rate of patients with critical illness has decreased significantly over the past two decades, but the rate of decline has slowed recently, with organ dysfunction as a major driver of morbidity and mortality. Among patients with the systemic inflammatory response syndrome (SIRS), acute lung injury is a common component with serious morbidity. Previous studies in our laboratory using a murine model of SIRS demonstrated a key role for NADPH oxidase 2 (Nox2)-derived reactive oxygen species in the resolution of inflammation. Nox2-deficient (gp91phox-/y) mice develop profound lung injury secondary to SIRS and fail to resolve inflammation. Alveolar macrophages from gp91phox-/y mice express greater levels of chemotactic and pro-inflammatory factors at baseline providing evidence that Nox2 in alveolar macrophages is critical for homeostasis. Based on the lung pathology with increased thrombosis in gp91phox-/y mice, and the known role of platelets in the inflammatory process, we hypothesized that Nox2 represses platelet activation. In the mouse model, we found that platelet-derived chemokine (C-X-C motif) ligand 4 (CXCL4) and CXCL7 were increased in the bronchoalveolar fluid of gp91phox-/y mice at baseline and 24 h post intraperitoneal zymosan-induced SIRS consistent with platelet activation. Activated platelets interact with leukocytes via P-selectin glycoprotein ligand 1 (PSGL-1). Within 2 h of SIRS induction, alveolar neutrophil PSGL-1 expression was higher in gp91phox-/y mice. Platelet-neutrophil interactions were decreased in the peripheral blood of gp91phox-/y mice consistent with movement of activated platelets to the lung of mice lacking Nox2. Based on the severe lung pathology and the role of platelets in the formation of neutrophil extracellular traps (NETs), we evaluated NET production. In contrast to previous studies demonstrating Nox2-dependent NET formation, staining of lung sections from mice 24 h post zymosan injection revealed a large number of citrullinated histone 3 (H3CIT) and myeloperoxidase positive cells consistent with NET formation in gp91phox-/y mice that was virtually absent in WT mice. In addition, H3CIT protein expression and PAD4 activity were higher in the lung of gp91phox-/y mice post SIRS induction. These results suggest that Nox2 plays a critical role in maintaining homeostasis by regulating platelet activation and NET formation in the lung.

Alveolar Macrophage Chemokine Secretion Mediates Neutrophilic Lung Injury in Nox2-Deficient Mice.

Acute lung injury (ALI), developing as a component of the systemic inflammatory response syndrome (SIRS), leads to significant morbidity and mortality. Reactive oxygen species (ROS), produced in part by the neutrophil NADPH oxidase 2 (Nox2), have been implicated in the pathogenesis of ALI. Previous studies in our laboratory demonstrated the development of pulmonary inflammation in Nox2-deficient (gp91phox-/y) mice that was absent in WT mice in a murine model of SIRS. Given this finding, we hypothesized that Nox2 in a resident cell in the lung, specifically the alveolar macrophage, has an essential anti-inflammatory role. Using a murine model of SIRS, we examined whole-lung digests and bronchoalveolar lavage fluid (BALf) from WT and gp91phox-/y mice. Both genotypes demonstrated neutrophil sequestration in the lung during SIRS, but neutrophil migration into the alveolar space was only present in the gp91phox-/y mice. Macrophage inflammatory protein (MIP)-1α gene expression and protein secretion were higher in whole-lung digest from uninjected gp91phox-/y mice compared to the WT mice. Gene expression of MIP-1α, MCP-1, and MIP-2 was upregulated in alveolar macrophages obtained from gp91phox-/y mice at baseline compared with WT mice. Further, ex vivo analysis of alveolar macrophages, but not bone marrow-derived macrophages or peritoneal macrophages, demonstrated higher gene expression of MIP-1α and MIP-2. Moreover, isolated lung polymorphonuclear neutrophils migrate to BALf obtained from gp91phox-/y mice, further providing evidence of a cell-specific anti-inflammatory role for Nox2 in alveolar macrophages. We speculate that Nox2 represses the development of inflammatory lung injury by modulating chemokine expression by the alveolar macrophage.

Neutrophil Phenotype Correlates With Postoperative Inflammatory Outcomes in Infants Undergoing Cardiopulmonary Bypass.

OBJECTIVES: Infants with congenital heart disease frequently require cardiopulmonary bypass, which causes systemic inflammation. The goal of this study was to determine if neutrophil phenotype and activation status predicts the development of inflammatory complications following cardiopulmonary bypass. DESIGN: Prospective cohort study. SETTING: Tertiary care PICU with postoperative cardiac care. PATIENTS: Thirty-seven patients 5 days to 10 months old with congenital heart disease requiring cardiopulmonary bypass. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Laboratory and clinical data collected included length of mechanical ventilation, acute kidney injury, and fluid overload. Neutrophils were isolated from whole blood at three time points surrounding cardiopulmonary bypass. Functional analyses included measurement of cell surface protein expression and nicotinamide adenine dinucleotide phosphate oxidase activity. Of all patients studied, 40.5% displayed priming of nicotinamide adenine dinucleotide phosphate oxidase activity in response to N-formyl-Met-Leu-Phe stimulation 24 hours post cardiopulmonary bypass as compared to pre bypass. Neonates who received steroids prior to bypass demonstrated enhanced priming of nicotinamide adenine dinucleotide phosphate oxidase activity at 48 hours. Patients who displayed priming post cardiopulmonary bypass were 8.8 times more likely to develop severe acute kidney injury as compared to nonprimers. Up-regulation of neutrophil surface CD11b levels pre- to postbypass occurred in 51.4% of patients, but this measure of neutrophil priming was not associated with acute kidney injury. Subsequent analyses of the basal neutrophil phenotype revealed that those with higher basal CD11b expression were significantly less likely to develop acute kidney injury. CONCLUSIONS: Neutrophil priming occurs in a subset of infants undergoing cardiopulmonary bypass. Acute kidney injury was more frequent in those patients who displayed priming of nicotinamide adenine dinucleotide phosphate oxidase activity after cardiopulmonary bypass. This pilot study suggests that neutrophil phenotypic signature could be used to predict inflammatory organ dysfunction.

Correction: Interferon Regulatory Factor 6 Has a Protective Role in the Host Response to Endotoxic Shock.

[This corrects the article DOI: 10.1371/journal.pone.0152385.].

Neutrophil azurophilic granule exocytosis is primed by TNF-α and partially regulated by NADPH oxidase.

Neutrophil (polymorphonuclear leukocyte) activation with release of granule contents plays an important role in the pathogenesis of acute lung injury, prompting clinical trials of inhibitors of neutrophil elastase. Despite mounting evidence for neutrophil-mediated host tissue damage in a variety of disease processes, mechanisms regulating azurophilic granule exocytosis at the plasma membrane, and thus release of elastase and other proteases, are poorly characterized. We hypothesized that azurophilic granule exocytosis would be enhanced under priming conditions similar to those seen during acute inflammatory events and during chronic inflammatory disease, and selected the cytokine TNF-α to model this in vitro. Neutrophils stimulated with TNF-α alone elicited intracellular reactive oxygen species (ROS) generation and mobilization of secretory vesicles, specific, and gelatinase granules. p38 and ERK1/2 MAPK were involved in these components of priming. TNF-α priming alone did not mobilize azurophilic granules to the cell surface, but did markedly increase elastase release into the extracellular space in response to secondary stimulation with N-formyl-Met-Leu-Phe (fMLF). Priming of fMLF-stimulated elastase release was further augmented in the absence of NADPH oxidase-derived ROS. Our findings provide a mechanism for host tissue damage during neutrophil-mediated inflammation and suggest a novel anti-inflammatory role for the NADPH oxidase.

Interferon Regulatory Factor 6 Has a Protective Role in the Host Response to Endotoxic Shock.

Interferon Regulatory Factor (IRF) 6, a member of the IRF family, is essential for epidermal and orofacial embryonic development. Irf6 is strongly expressed in keratinocytes, in which it regulates epidermal proliferation, differentiation, and migration. A recent role for Irf6 in Toll-like receptor 2-dependent chemokine gene expression was also reported in an epithelial cell line. However, a function for Irf6 in innate immune cells was not previously reported. In the present study, we investigated the expression and function of Irf6 in bone marrow-derived neutrophils and macrophages. We show here, using a conditional knockout of Irf6 in lysosymeM expressing cells, that Irf6 is required for resistance to LPS-induced endotoxic shock. In addition, Irf6-deficient bone marrow-derived neutrophils exhibited increased chemotactic index and velocity compared with wild-type cells in vitro. TLR4-specific KC and IL6 secretions were upregulated in Irf6-deficient bone marrow-derived macrophages in vitro. These cells also exhibited an increased level of phosphorylated IkBa. Collectively, our findings suggest a role for Irf6 in the resistance to endotoxic shock due to NFk-B-mediated alteration of cytokine production.

A Common Genetic Variant in TLR1 Enhances Human Neutrophil Priming and Impacts Length of Intensive Care Stay in Pediatric Sepsis.

Polymorphonuclear leukocytes (PMN) achieve an intermediate or primed state of activation following stimulation with certain agonists. Primed PMN have enhanced responsiveness to subsequent stimuli, which can be beneficial in eliminating microbes but may cause host tissue damage in certain disease contexts, including sepsis. As PMN priming by TLR4 agonists is well described, we hypothesized that ligation of TLR2/1 or TLR2/6 would prime PMN. Surprisingly, PMN from only a subset of donors were primed in response to the TLR2/1 agonist, Pam3CSK4, although PMN from all donors were primed by the TLR2/6 agonist, FSL-1. Priming responses included generation of intracellular and extracellular reactive oxygen species, MAPK phosphorylation, integrin activation, secondary granule exocytosis, and cytokine secretion. Genotyping studies revealed that PMN responsiveness to Pam3CSK4 was enhanced by a common single-nucleotide polymorphism (SNP) in TLR1 (rs5743618). Notably, PMN from donors with the SNP had higher surface levels of TLR1 and were demonstrated to have enhanced association of TLR1 with the endoplasmic reticulum chaperone gp96. We analyzed TLR1 genotypes in a pediatric sepsis database and found that patients with sepsis or septic shock who had a positive blood culture and were homozygous for the SNP associated with neutrophil priming had prolonged pediatric intensive care unit length of stay. We conclude that this TLR1 SNP leads to excessive PMN priming in response to cell stimulation. Based on our finding that septic children with this SNP had longer pediatric intensive care unit stays, we speculate that this SNP results in hyperinflammation in diseases such as sepsis.

Evaluation of hematologic variables in newborn C57/BL6 mice up to day 35.

BACKGROUND: Hematologic variables are often analyzed in animal analogs during the investigation of complex disease etiologies such as necrotizing enterocolitis. However, reference intervals (RI) can vary depending on animal strain, age, and sampling site. Reference intervals have been published for adult C57BL/6J mice, but not newborn C57BL/6J mice. OBJECTIVES: The purpose of the present study was to determine hematologic RI in newborn C57BL/6J mice up to day 35. METHODS: C57BL/6J mice founders from The Jackson Laboratory were bred at the University of Iowa. Blood samples were obtained via facial vein sampling at postnatal days 0 (p0), p7, p14, p21, p28, or young adulthood (p35). CBCs were determined with the Sysmex XT-2000iV analyzer within 30 minutes of blood collection at a 1:10 dilution. Statistics were determined using nonparametric methods following ASVCP guidelines. RESULTS: Hematologic RI were determined for each of the 6 groups (n = 247, n ≥ 39 per group). Significantly higher values for HGB, RBC, and PLT counts were observed with advancing developmental age. Total WBC counts remained relatively stable during the first 35 days of life. However, WBC differential counts were dominated by neutrophils and lymphocytes in the younger mice, with a trend toward a lymphocytic leukogram on day 35. CONCLUSIONS: These results illustrate the dynamic changes in hematologic variables during murine development after birth. Utilization of age-specific RI is advised when evaluating data derived from experimental perinatal mouse models.

NOX2 protects against progressive lung injury and multiple organ dysfunction syndrome.

Systemic inflammatory response syndrome (SIRS) is a common clinical condition in patients in intensive care units that can lead to complications, including multiple organ dysfunction syndrome (MODS). MODS carries a high mortality rate, and it is unclear why some patients resolve SIRS, whereas others develop MODS. Although oxidant stress has been implicated in the development of MODS, several recent studies have demonstrated a requirement for NADPH oxidase 2 (NOX2)-derived oxidants in limiting inflammation. We recently demonstrated that NOX2 protects against lung injury and mortality in a murine model of SIRS. In the present study, we investigated the role of NOX2-derived oxidants in the progression from SIRS to MODS. Using a murine model of sterile systemic inflammation, we observed significantly greater illness and subacute mortality in gp91(phox-/y) (NOX2-deficient) mice compared with wild-type mice. Cellular analysis revealed continued neutrophil recruitment to the peritoneum and lungs of the NOX2-deficient mice and altered activation states of both neutrophils and macrophages. Histological examination showed multiple organ pathology indicative of MODS in the NOX2-deficient mice, and several inflammatory cytokines were elevated in lungs of the NOX2-deficient mice. Overall, these data suggest that NOX2 function protects against the development of MODS and is required for normal resolution of systemic inflammation.

ROS-containing endosomal compartments: implications for signaling.

The endogenous generation of reactive oxygen species (ROS), previously perceived as a detrimental by-product of cellular processes, is now recognized as a critical component of intracellular signaling. Exploration of these biological signaling functions requires understanding the complex redox biochemistry and recognizing the compartment-specific elements of ROS generation. The endosomal compartment is increasingly recognized as a source for NADPH oxidase (NOX)-generated signaling ROS. Despite this growing understanding, there are significant limitations to the available detection and measurement systems for endogenous ROS. This chapter provides information about specific methodologies and redox-sensitive probes to guide the investigator and define the critical limitations for many of the available approaches. Although measurement continues to be challenging, the rapid growth and development of new detection systems suggests that our capacity to assign specific signaling roles to endosomal ROS will expand markedly in the next several years.