Diminished priming of neonatal polymorphonuclear leukocytes by lipopolysaccharide is associated with reduced CD14 expression

Selective modulation of monocyte and neutrophil responses with activated protein C in preterm infants

BACKGROUND

Inflammation is associated with many disorders of preterm infants including periventricular leukomalacia, chronic lung disease, and necrotizing enterocolitis. Activated protein c (APC) has shown positive immunomodulatory effects.

OBJECTIVES

We aimed to study neutrophil and monocyte function in response to lipopolysaccharide (LPS) and APC stimulation ex vivo in preterm infants <32 weeks gestation over the first week of life compared to neonatal and adult controls.

METHODS

Peripheral blood was taken on day 1, 3, and 7 and stimulated with LPS in the absence or presence of APC. Expression of toll-like receptor 4 (TLR4) and CD11b and reactive oxygen intermediate (ROI) release from neutrophils and monocytes was examined by flow cytometry.

RESULTS

LPS induced neutrophil ROI in adults and preterm infants and was significantly reduced by APC. Baseline and LPS-induced monocyte ROI production in preterm neonates was increased compared to adult and term controls. Neutrophil TLR4 baseline expression was higher in term controls compared to preterm infants.

CONCLUSION

Increased systemic ROI release in preterm infants may mediate tissue damage, ROI was reduced by APC. However, due to the high risk of hemorrhage further examination of APC mutant forms with anti-inflammatory but decreased anticoagulant properties is merited.

Monoclonal Antibody to CD14, TLR4, or CD11b: Impact of Epitope and Isotype Specificity on ROS Generation by Human Granulocytes and Monocytes

Lipopolysaccharides (LPSs or endotoxins) from Gram-negative bacteria represent pathogen-associated molecular patterns (PAMPs) that are recognized by CD14 and Toll-like receptor 4 (TLR4). Lipopolysaccharides prime polymorphonuclear leukocytes (PMNs) for substantial production of reactive oxygen species (ROS) during its response to secondary stimuli such as chemoattractants or pathogens. The excessive ROS production can damage surrounding host tissues, thereby amplifying the inflammatory reaction caused by pathogens. Today, specific antibodies against CD14, TLR4, and CD11b are being used as the essential tools to elucidate the role of these receptors in acute inflammation and some of these antibodies have advised as therapeutic agents for clinical use. Because each antibody has two antigen-binding arms [F(ab′)₂] and one Fc arm, its effect on cellular response is much more complicated rather than simple blockage of target receptor. In fact, IgG antibody, once bound to target receptor, engages Fc receptors γ (FcγRs) and thereby is able to activate the adaptive immune system. The consequences of antibody-dependent binary heterotypic association of CD14, TLR4, or CD11b with FcγRs as well as homotypic one on ROS production are not well elucidated. Moreover, the consequences of antigenic recognition of CD14, TLR4, or CD11b by specific F(ab′)₂ fragments are not always investigated. In this review, we will discuss known mechanisms underlying the therapeutic efficiency of CD14, TLR4, and CD11b/CD18 antibodies with a focus on LPS-dependent ROS or cytokine production by PMNs or monocytes. The impacts of F(ab′)₂ as well as antibody IgG subclasses (isotypes) in therapeutic efficiency or agonistic potency of known antibodies against abovementioned receptors are presented. We also pay attention to how the efficiency of different IgG antibody subclasses is modulated during LPS-induced inflammation and by production of priming agents such as interferon γ (IFN-γ). Our review reinforces the molecular targets and therapeutic approaches to amelioration of harmful consequences of excessive activation of human pattern recognition receptors.

Impact of CD14 on Reactive Oxygen Species Production from Human Leukocytes Primed by Escherichia coli Lipopolysaccharides

Lipopolysaccharides (LPS) from Gram-negative bacteria prime human polymorphonuclear neutrophils (PMNs) via multicomponent receptor cluster including CD14 and MD-2·TLR4 for the enhanced release of reactive oxygen species (ROS) were triggered by bacterial derived peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP). In this study, we investigated the impact of CD14 on LPS-induced priming of human PMNs for fMLP-triggered ROS generation (respiratory or oxidative) burst. Monoclonal antibodies against human CD14 (mAbs) as well as isotype-matched IgG2a did not influence significantly fMLP-triggered ROS production from LPS-unprimed PMNs. Anti-CD14 mAbs (clone UCHM-1) attenuated LPS-induced priming of PMNs as it had been mirrored by fMLP-triggered decrease of ROS production. Similar priming activity of S-LPS or Re-LPS from Escherichia coli for fMLP-triggered ROS release from PMNs was found. Obtained results suggest that glycosylphosphatidylinositol-anchored CD14 is the key player in LPS-induced PMN priming for fMLP-triggered ROS production. We believe that blockade of CD14 on the cell surface and clinical use of anti-CD14 mAbs or their Fab fragments may diminish the production of ROS and improve outcomes during cardiovascular diseases manifested by LPS-induced inflammation.

CD71+ erythroid cells from neonates born to women with preterm labor regulate cytokine and cellular responses

Neonatal CD71+ erythroid cells are thought to have immunosuppressive functions. Recently, we demonstrated that CD71+ erythroid cells from neonates born to women who underwent spontaneous preterm labor (PTL) are reduced to levels similar to those of term neonates; yet, their functional properties are unknown. Herein, we investigated the functionality of CD71+ erythroid cells from neonates born to women who underwent spontaneous preterm or term labor. CD71+ erythroid cells from neonates born to women who underwent PTL displayed a similar mRNA profile to that of those from term neonates. The direct contact between preterm or term neonatal CD71+ erythroid cells and maternal mononuclear immune cells, but not soluble products from these cells, induced the release of proinflammatory cytokines and a reduction in the release of TGF-β. Moreover, PTL-derived neonatal CD71+ erythroid cells (1) modestly altered CD8+ T cell activation; (2) inhibited conventional CD4+ and CD8+ T-cell expansion; (3) suppressed the expansion of CD8+ regulatory T cells; (4) regulated cytokine responses mounted by myeloid cells in the presence of a microbial product; and (5) indirectly modulated T-cell cytokine responses. In conclusion, neonatal CD71+ erythroid cells regulate neonatal T-cell and myeloid responses and their direct contact with maternal mononuclear cells induces a proinflammatory response. These findings provide insight into the biology of neonatal CD71+ erythroid cells during the physiologic and pathologic processes of labor.

Innate immunity of the human newborn: distinct cytokine responses to LPS and other Toll-like receptor agonists

Human newborns are at increased risk of microbial invasion and display diminished responses to many vaccines indicating a functional immaturity of the immune system at birth. Such altered immune reactivity may reflect the demands of in utero existence, including the need to avoid potentially harmful inflammatory immune reactions. Despite normal basal expression of Toll-like receptors and membrane CD14, innate immune responses of neonatal mononuclear cells to lipopolysaccharide are characterized by markedly reduced release of the pro-inflammatory Th1-polarizing cytokines TNF-α and interferon-γ with relative preservation of anti-inflammatory Th2-polarizing cytokines. Differences between newborns and adults with respect to TLR-induced TNF-α release extend to a range of TLR agonists, including bacterial lipopeptides, and are due to differences in soluble factors present in blood plasma. Soluble factors in neonatal blood plasma suppress TLR-induced TNF-α release from monocytes and efforts to identify and characterize these inhibitors are on-going. Such altered immunity to TLR agonists is likely to alter both innate and adaptive immune responses in newborns profoundly. Definition of the mechanisms underlying distinct neonatal immunity promises to identify novel ways to prevent and treat infection in this relatively high-risk population.

Role of CD11b/CD18 in priming of human leukocytes by endotoxin glycoforms from Escherichia coli

The primary objective of this study was to determine the role of β2 integrin α-subunit (CD11b) in the mechanism of human polymorphonuclear leukocyte (PML) priming by S or Re endotoxin glycoforms from Escherichia coli for fMLP-induced respiratory burst. Similar priming activity of S and Re endotoxin glycoforms for fMLP-induced reactive oxygen species (ROS) generation from primed PML was found. Anti-CD11b antibodies (clone ICRF 44) as well as isotype-matched immunoglobulin G1 (clone MOPC-21) do not influence the fMLP-induced ROS generation from unprimed PML. Antibodies against CD11b do not change fMLP-induced ROS generation from endotoxin-primed PML as well. The involvement of different isoforms of Fcγ receptors in fMLP-induced ROS generation from activated PML is proposed.

Mechanisms of acute respiratory distress syndrome in children and adults: a review and suggestions for future research

OBJECTIVES

To provide a current overview of the epidemiology and pathophysiology of acute respiratory distress syndrome in adults and children, and to identify research questions that will address the differences between adults and children with acute respiratory distress syndrome.

DATA SOURCES

Narrative literature review and author-generated data.

DATA SELECTION

The epidemiology of acute respiratory distress syndrome in adults and children, lung morphogenesis, and postnatal lung growth and development are reviewed. The pathophysiology of acute respiratory distress syndrome is divided into eight categories: alveolar fluid transport, surfactant, innate immunity, apoptosis, coagulation, direct alveolar epithelial injury by bacterial products, ventilator-associated lung injury, and repair.

DATA EXTRACTION AND SYNTHESIS

Epidemiologic data suggest significant differences in the prevalence and mortality of acute respiratory distress syndrome between children and adults. Postnatal lung development continues through attainment of adult height, and there is overlap between the regulation of postnatal lung development and inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms. Therefore, there is a different biological baseline network of gene and protein expression in children as compared with adults.

CONCLUSIONS

There are significant obstacles to performing research on children with acute respiratory distress syndrome. However, epidemiologic, clinical, and animal studies suggest age-dependent differences in the pathophysiology of acute respiratory distress syndrome. In order to reduce the prevalence and improve the outcome of patients with acute respiratory distress syndrome, translational studies of inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms are needed. Understanding the differences in pathophysiologic mechanisms in acute respiratory distress syndrome between children and adults should facilitate identification of novel therapeutic interventions to prevent or modulate lung injury and improve lung repair.

The Innate Immune System of the Perinatal Lung and Responses to Respiratory Syncytial Virus Infection

The response of the preterm and newborn lung to airborne pathogens, particles, and other insults is initially dependent on innate immune responses since adaptive responses may not fully mature and require weeks for sufficient responses to antigenic stimuli. Foreign material and microbial agents trigger soluble, cell surface, and cytoplasmic receptors that activate signaling cascades that invoke release of surfactant proteins, defensins, interferons, lactoferrin, oxidative products, and other innate immune substances that have antimicrobial activity, which can also influence adaptive responses. For viral infections such as respiratory syncytial virus (RSV), the pulmonary innate immune responses has an essential role in defense as there are no fully effective vaccines or therapies for RSV infections of humans and reinfections are common. Understanding the innate immune response by the preterm and newborn lung may lead to preventive strategies and more effective therapeutic regimens.

Perinatal lamb model of respiratory syncytial virus (RSV) infection

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. Many animal models are used to study RSV, but most studies investigate disease in adult animals which does not address the unique physiology and immunology that makes infants more susceptible. The perinatal (preterm and term) lamb is a useful model of infant RSV disease as lambs have similar pulmonary structure including airway branching, Clara and type II cells, submucosal glands and Duox/lactoperoxidase (LPO) oxidative system, and prenatal alveologenesis. Lambs can be born preterm (90% gestation) and survive for experimentation although both preterm and term lambs are susceptible to ovine, bovine and human strains of RSV and develop clinical symptoms including fever, tachypnea, and malaise as well as mild to moderate gross and histologic lesions including bronchiolitis with epithelial injury, neutrophil infiltration and syncytial cell formation. RSV disease in preterm lambs is more severe than in term lambs; disease is progressively less in adults and age-dependent susceptibility is a feature similar to humans. Innate and adaptive immune responses by perinatal lambs closely parallel those of infants. The model is used to test therapeutic regimens, risk factors such as maternal ethanol consumption, and formalin inactivated RSV vaccines.

Human neonatal peripheral blood leukocytes demonstrate pathogen-specific coordinate expression of TLR2, TLR4/MD2, and MyD88 during bacterial infection in vivo

Toll-like receptors (TLRs) play important roles in infection. We have previously reported TLR2 is up-regulated in neonatal Gram-positive (G+) bacteremia, whereas TLR4 is up-regulated in neonatal Gram-negative (G-) bacteremia. For functional signaling, TLR4 requires myeloid differentiation (MD)-2, and both TLR2 and TLR4 signal need myeloid differentiation factor (MyD88). However, it is unknown whether newborns can enhance expression of MD-2 and MyD88 with bacterial infection in coordination with TLR expression. We characterized neonatal peripheral blood leukocyte expression of MD-2 and MyD88 in relation to TLR2/4 in newborns. TLR2 mRNA expression by PBMCs and TLR2 protein expression by monocytes and granulocytes were significantly increased in the G+ bacteremia group. TLR4 mRNA on PMBCs and protein expression on monocytes and granulocytes were significantly increased in the G- bacterial group. Remarkably, although, MyD88 mRNA was increased in all patients with documented bacterial infection and correlated with both TLR2 and TLR4, MD-2 mRNA was selectively increased in G- bacterial group, wherein it correlated with TLR4 but not with TLR2 mRNA. Our findings demonstrate that during bacterial infection in vivo, newborns selectively and coordinately amplify the TLR2-MyD88 pathway in G+ bacterial infection and the TLR4/MD2/MyD88 pathway in G- bacterial infection, suggesting key roles for innate immune pathway in neonatal responses to bacterial infection.

Effects of age on the synergistic interactions between lipopolysaccharide and mechanical ventilation in mice

Children have a lower incidence and mortality from acute lung injury (ALI) than adults, and infections are the most common event associated with ALI. To study the effects of age on susceptibility to ALI, we investigated the responses to microbial products combined with mechanical ventilation (MV) in juvenile (21-d-old) and adult (16-wk-old) mice. Juvenile and adult C57BL/6 mice were treated with inhaled Escherichia coli 0111:B4 lipopolysaccharide (LPS) and MV using tidal volume = 15 ml/kg. Comparison groups included mice treated with LPS or MV alone and untreated age-matched control mice. In adult animals treated for 3 hours, LPS plus MV caused synergistic increases in neutrophils (P < 0.01) and IgM in bronchoalveolar lavage fluid (P = 0.03) and IL-1β in whole lung homogenates (P < 0.01) as compared with either modality alone. Although juvenile and adult mice had similar responses to LPS or MV alone, the synergistic interactions between LPS and MV did not occur in juvenile mice. Computational analysis of gene expression array data suggest that the acquisition of synergy with increasing age results, in part, from the loss of antiapoptotic responses and the acquisition of proinflammatory responses to the combination of LPS and MV. These data suggest that the synergistic inflammatory and injury responses to inhaled LPS combined with MV are acquired with age as a result of coordinated changes in gene expression of inflammatory, apoptotic, and TGF-β pathways.

Distinct roles of TLR4 and CD14 in LPS-induced inflammatory responses of neonates

During infections, pathogens bind to toll-like receptor (TLR)4 and CD14 receptors and induce cytokine release, leading to inflammation. Here, we investigated TLR4 and CD14 expression on peripheral blood leukocytes (PBLs) and their roles in lipopolysaccharide (LPS)-induced cytokine and chemokine release. Full-term and preterm neonates and adults were studied. PBLs were pretreated with anti-TLR4- and anti-CD14-blocking antibodies and stimulated with LPS. Cytokine and chemokine levels were measured in supernatants. TLR4, CD14 expression, and LPS-induced CXCL8 release were higher in neonates, possibly contributing to aberrant inflammation. TLR4 blockade resulted in approximately 3-fold greater suppression of LPS-induced CXCL8 release in preterm neonates (38%) than in adults (14%). CD14 blockade (approximately 80%) in neonates induced approximately 3-fold greater inhibition of CXCL8 release, compared with anti-TLR4 (approximately 30%). Anti-TLR4 partly (50-60%) inhibited IL-10 and TNF-alpha, whereas anti-CD14 completely suppressed their release. Our findings reveal that neonates depend more on TLR4 for CXCL8 release. Furthermore, neonatal LPS-induced CXCL8 release, apart from TLR4/CD14-mediated signaling, is regulated by LPS interactions with other TLRs and/or immune receptors. IL-10 and TNF-alpha release depends on LPS binding not only to CD14/TLR4 but also to CD14 associated with another TLR. Our findings reveal the contribution of TLR4 and CD14 in neonatal cytokine and chemokine release and could aid in design of antagonists to prevent harmful inflammation.

Age-dependent changes of proinflammatory cytokine production by porcine peripheral blood phagocytes

The aim of the present study was to determine postnatal ontogeny of proinflammatory cytokines IL-1beta, IL-8 and TNF-alpha production by in vitro stimulated porcine blood leukocytes. Four age categories of pigs were chosen. Cytokine production was determined using intracellular flow cytometry. It was found that IL-8 and TNF-alpha production by blood monocytes significantly increased during the postnatal period while production of IL-1beta remained unchanged. In blood neutrophils, the IL-8 production increased only during the postnatal period, while the levels of TNF-alpha and IL-1beta were undetectable during the whole postnatal period. Generally, the most intensive changes in cytokine production occurred before weaning. The production of low levels of cytokines by monocytes and neutrophils from young pigs was not caused by a delayed cytokine response because the cytokine production after 8-h stimulation was lower than that after 4-h stimulation in all age categories. The ontogenetical changes showed the same trends when two different stimulators (LPS, heat-inactivated E. coli) were used, suggesting that the ontogenetical changes are not caused by a simple defect in one signalling pathway, but it is probably a more complex process. No differences in cytokine production between the whole blood and the isolated cells supplemented with newborn or adult serum were found. Thus the ability of newborn monocytes and neutrophils to produce proinflammatory cytokines was not decreased due to the influence of composition of the microenvironment, where the cells were present. In conclusion, the ability of porcine blood leukocytes to produce cytokines develops during postnatal life.

Innate immunity of the newborn: basic mechanisms and clinical correlates

The fetus and newborn face a complex set of immunological demands, including protection against infection, avoidance of harmful inflammatory immune responses that can lead to pre-term delivery, and balancing the transition from a sterile intra-uterine environment to a world that is rich in foreign antigens. These demands shape a distinct neonatal innate immune system that is biased against the production of pro-inflammatory cytokines. This bias renders newborns at risk of infection and impairs responses to many vaccines. This Review describes innate immunity in newborns and discusses how this knowledge might be used to prevent and treat infection in this vulnerable population.

Interferon regulatory factor 3-dependent responses to lipopolysaccharide are selectively blunted in cord blood cells

The synthesis of interferon-β (IFNβ) and IFN-inducible factors elicited by lipopolysaccharide (LPS) depends on the transcriptional activity of interferon regulatory factor 3 (IRF-3) downstream of Toll-like receptor-4 (TLR4). To examine the ability of human newborns to mount TLR4-mediated IRF-3–dependent responses, we analyzed the pattern of genes expressed on the addition of LPS to cord blood or cord blood monocyte-derived dendritic cells (moDCs). Expression of IFNβ and IFN-inducible genes was selectively impaired in neonatal blood and moDCs as compared with their adult counterparts. This selective defect was confirmed by microarray experiments on moDCs. Altered expression of IFN-inducible genes was related to impaired IFNβ synthesis because IFNβ signaling was functional in neonatal moDCs. However, addition of exogenous IFNβ failed to restore LPS-induced IL-12p70 synthesis which was previously shown to be defective in neonatal moDCs. Although LPS-induced IRF-3 nuclear translocation was observed both in adult and neonatal moDCs, IRF-3 DNA-binding activity and association with the coactivator CREB-binding protein (CBP) were decreased in neonatal as compared with adult moDCs. We conclude that impaired IRF-3/CBP interaction in neonatal blood cells exposed to LPS is associated with impaired expression of IFNβ and IFN-inducible genes. Because IRF-3 activity is also required for IL-12p70 synthesis, our findings provide a molecular basis for the decreased ability of LPS-stimulated neonatal moDCs to elicit Th1-type responses.

Mechanisms underlying reduced apoptosis in neonatal neutrophils

Apoptosis, which leads to phagocytosis by mononuclear cells, represents the primary mechanism for removing neutrophils from inflamed tissues and minimizing injury. The present studies show that membrane phosphatidylserine turnover and permeability, as well as DNA fragmentation, were reduced in neutrophils from neonates when compared with adults. The activity of caspase 3 and expression of the proapoptotic proteins Bax, Bad, and Bak were also decreased in neonatal relative to adult neutrophils. These findings are consistent with impaired apoptosis in neonatal cells, which may contribute to prolonged inflammation in infants after oxidative stress or infection. Neutrophil apoptosis is induced by endogenous ligands such as Fas (FasL), which engage death receptors of the tumor necrosis factor/nerve growth factor superfamily, including Fas receptor (FasR). We found that expression of FasR was decreased in neonatal when compared with adult cells. Moreover, neonatal neutrophils did not undergo apoptosis in response to anti-FasR antibody and exhibited impaired chemotaxis to soluble FasL. However, in both adult and neonatal cells, p38 mitogen-activated protein kinase and phosphatidylinositol 3-kinase inhibitors blocked Fas-induced activity. These data suggest that prolonged survival of neonatal neutrophils at injured sites is due, in part, to reduced responsiveness to FasL. This may be related to decreased expression of both FasR and Bcl-2-family proteins that mediate neutrophil apoptosis.

Role of protein tyrosine kinase p53/56lyn in diminished lipopolysaccharide priming of formylmethionylleucyl- phenylalanine-induced superoxide production in human newborn neutrophils

Human newborns are more susceptible than adults to bacterial infection. With gram-negative bacteria, this may be due to a diminished response of newborn leukocytes to lipopolysaccharide (LPS). Since protein tyrosine kinase inhibition abolishes LPS priming in adult cells, we hypothesized that protein tyrosine kinases may have a critical role in LPS priming of polymorphonuclear neutrophils (PMNs) and that newborn PMNs may have altered protein tyrosine kinase activities. In the present study, we investigated the role of src family protein tyrosine kinases in the LPS response of newborn PMNs compared to adult cells. In a respiratory assay, the LPS-primed increase in formylmethionylleucylphenylalanine (fMLP)-triggered O2- release by adult PMNs was greatly decreased by PP1 [4-amino-5-(4-methyphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine], a src kinase inhibitor, to the level of untreated newborn PMNs, in which LPS failed to prime. LPS activated the src-like kinases p59hck (HCK) and p58fgr (FGR) in both adult and newborn PMNs but increased the activation of p53/56lyn (LYN) only in adult cells. In newborn PMNs, LYN was highly phosphorylated independent of LPS. We evaluated subcellular fractions of PMNs and found that the phosphorylated form of LYN was mainly in the Triton-extractable, cytosolic fraction in adult PMNs, while in newborn cells it was located mainly in Triton-insoluble, granule- and membrane-associated fractions. In contrast, the phosphorylated mitogen-activated protein kinases ERK1/2 and p38 were mainly detected in the cytosol in both adult and newborn PMNs. These data indicate a role for LYN in the regulation of LPS priming. The trapping of phosphorylated LYN in the membrane-granule fraction in newborn PMNs may contribute to the deficiency of newborn cells in responding to LPS stimulation.

Role of MyD88 in diminished tumor necrosis factor alpha production by newborn mononuclear cells in response to lipopolysaccharide

Human newborns are more susceptible than adults to infection by gram-negative bacteria. We hypothesized that this susceptibility may be associated with a decreased response by leukocytes to lipopolysaccharide (LPS). In this study, we compared LPS-induced secretion of tumor necrosis factor alpha (TNF-alpha) by mononuclear cells (MNC) from adult peripheral blood and newborn umbilical cord blood in vitro and attempted to determine the mechanisms involved in its regulation. At a high concentration of LPS (10 ng/ml) and in the presence of autologous plasma, MNC from adults and newborns secreted similar amounts of TNF-alpha. However, in the absence of plasma, MNC from newborns secreted significantly less TNF-alpha compared to MNC from adults. Moreover, at a low concentration of LPS (0.1 ng/ml) and in the presence of plasma, TNF-alpha secretion was significantly lower for newborn MNC compared to adult MNC. Adults and newborns had similar numbers of CD14 and Toll-like receptor 4 (TLR-4)-positive cells as measured by flow cytometry. However, the intensity of the CD14 marker was greater for adult than for newborn cells. Incubation of cells with LPS led to an increase in CD14 and TLR-4 intensity for adult cells but not for newborn cells. The effect of LPS stimulation of adult or newborn cells was similar for ERK, p38, and IkappaBalpha phosphorylation, as well as IkappaBalpha degradation. Finally, we assessed levels of the TLR-4 adapter protein, the myeloid differentiation antigen 88 (MyD88). We found a direct relation between adult and newborn TNF-alpha secretion and MyD88, which was significantly decreased in newborn monocytes. Since TLR-4 signals intracellularly through the adapter protein, MyD88, we hypothesize that MyD88-dependent factors are responsible for delayed and decreased TNF-alpha secretion in newborn monocytes.

Impaired CD14-dependent and independent response of polymorphonuclear leukocytes in preterm infants

Preterm newborn infants are especially susceptible to Gram-negative sepsis that is associated with a lethality of up to 40%.

AIMS

We tested whether polymorphonuclear leukocytes (PMN) from preterm infants exhibit an impaired antibacterial response upon stimulation with lipopolysaccharide (LPS) from Escherichia coli when compared to full term newborns or adults.

METHODS

We studied the effect of LPS on the expression of the surface proteins CD11b and CD14 and the secretion of elastase by PMN from preterm infants, term infants and adults ex vivo.

RESULTS

We found a significantly reduced antibacterial activity of PMN from preterm infants upon stimulation with LPS as indicated by low surface expression of the adhesion molecule CD11b and the reduced secretion of PMN elastase. LPS-induced CD11b expression was dependent on binding of LPS to the surface protein CD14 as CD14 antibodies inhibited LPS dependent CD11b upregulation. Furthermore CD14 expression was lower on PMN from preterm infants than from adults. In addition, CD14 independent upregulation of CD11b in response to tumor necrosis factor (TNF-alpha), N-formyl peptides (FMLP) and phorbol ester (PMA) was impaired.

CONCLUSION

PMN from preterm infants are distinctly hyporesponsive to LPS, which may explain the predisposition of these children to invasive disease due to gramnegative bacteria.

LPS-induced lung injury in neonatal rats: changes in gelatinase activities and consequences on lung growth

Postnatal lung growth disorders may involve imbalance between metalloproteinases and their inhibitors. Inflammatory cell 92-kDa gelatinase overactivity has been reported in adults with lung injury but has not been looked for in neonates. We compared gelatinase activity in neonatal and adult rats and evaluated postnatal lung growth after lipopolysaccharide (LPS)-induced lung injury. Significant intra-alveolar inflammatory cell recruitment occurred in adults and neonates; cell counts increased 16-fold in adults and 2.7-fold in neonates. Total 92-kDa gelatinase activity was increased in neonates and adults and was significantly correlated to inflammatory cell counts. For a given cell count, 92-kDa gelatinase increased more in neonates than in adults. Morphometric neonatal lung analysis showed that LPS-injured lungs had decreases in absolute values of lung volume (P < 0.03), alveolar surface (P < 0.004), and air space volume (P < 0.03). Doxycycline, a nonspecific metalloproteinase inhibitor, partly inhibited LPS-induced 92-kDa gelatinase overactivity but did not improve LPS-induced alveolar growth disorders. LPS-mediated lung injury in neonatal rats induced both gelatinase B overactivity and alveolar growth disorders, although no causal link between these two effects was demonstrated.

Mechanisms underlying reduced responsiveness of neonatal neutrophils to distinct chemoattractants

Potential mechanisms underlying impaired chemotactic responsiveness of neonatal neutrophils were investigated. Two distinct chemoattractants were compared: bacterially derived N-formyl-methionyl-leucyl-phenylalanine (fMLP) and a unique chemotactic monoclonal antibody, designated DL1.2, which binds to a neutrophil antigen with an apparent molecular mass of 120 kDa. Chemotaxis of neutrophils toward fMLP, as well as DL1.2, was reduced in neonates when compared with adult cells. This did not appear to be a result of decreased fMLP receptor or DL1.2 antigen expression by neonatal neutrophils. fMLP, but not DL1.2, induced a rapid increase in intracellular calcium in adult and neonatal cells, which reached a maximum within 30 s. The calcium response of cells from neonates to fMLP was reduced when compared with adult cells, and an unresponsive subpopulation of neonatal neutrophils was identified. NF-kappaB nuclear binding activity induced by fMLP and DL1.2, as well as expression of the p65 NF-kappaB subunit and IkappaB-alpha, was also significantly reduced in neonatal cells, when compared with adult cells. In contrast, although fMLP, but not DL1.2, activated p42/44 and p38 mitogen-activated protein (MAP) kinases in neutrophils, no differences were observed between adults and neonates. Chemotaxis of adult and neonatal neutrophils toward fMLP and DL1.2 was also blocked to a similar extent by inhibitors of phosphatidylinositol 3-kinase, as well as an inhibitor of NF-kappaB. These findings indicate that reduced chemotactic responsiveness in neonatal neutrophils is a result of, at least in part, aberrations in chemoattractant-induced signaling. However, the biochemical pathways mediating this defect appear to be related to the specific chemoattractant.

Polyunsaturated fatty acids and T-cell function: implications for the neonate

Infant survival depends on the ability to respond effectively and appropriately to environmental challenges. Infants are born with a degree of immunological immaturity that renders them susceptible to infection and abnormal dietary responses (allergies). T-lymphocyte function is poorly developed at birth. The reduced ability of infants to respond to mitogens may be the result of the low number of CD45RO+ (memory/antigen-primed) T cells in the infant or the limited ability to produce cytokines [particularly interferon-y, interleukin (IL)-4, and IL-10. There have been many important changes in optimizing breast milk substitutes for infants; however, few have been directed at replacing factors in breast milk that convey immune benefits. Recent research has been directed at the neurological, retinal, and membrane benefits of adding 20:4n-6 (arachidonic acid; AA) and 22:6n-3 (docosahexaenoic acid; DHA) to infant formula. In adults and animals, feeding DHA affects T-cell function. However, the effect of these lipids on the development and function of the infant's immune system is not known. We recently reported the effect of adding DHA + AA to a standard infant formula on several functional indices of immune development. Compared with standard formula, feeding a formula containing DHA + AA increased the proportion of antigen mature (CD45RO+) CD4+ cells, improved IL-10 production, and reduced IL-2 production to levels not different from those of human milk-fed infants. This review will briefly describe T-cell development and the potential immune effect of feeding long-chain polyunsaturated fatty acids to the neonate.

Activation of extracellular signal-related protein kinases 1 and 2 of the mitogen-activated protein kinase family by lipopolysaccharide requires plasma in neutrophils from adults and newborns

Neutrophils exposed to low concentrations of gram-negative lipopolysaccharide (LPS) become primed and have an increased oxidative response to a second stimulus (e.g., formyl-methionyl-leucyl-phenylalanine [fMLP]). In studies aimed at understanding newborn sepsis, we have shown that neutrophils of newborns are not primed in response to LPS. To further understand the processes involved in LPS-mediated priming of neutrophils, we explored the role of extracellular signal-related protein kinases (ERK 1 and 2) of the mitogen-activated protein kinase family. We found that LPS activated ERK 1 and 2 in cells of both adults and newborns and that activation was plasma dependent (maximal at > or =5%) through LPS-binding protein. Although fibronectin in plasma is required for LPS-mediated priming of neutrophils of adults assessed by fMLP-triggered oxidative burst, it was not required for LPS-mediated activation of ERK 1 and 2. LPS-mediated activation was dose and time dependent; maximal activation occurred with approximately 5 ng of LPS per ml and at 10 to 40 min. We used the inhibitor PD 98059 to study the role of ERK 1 and 2 in the LPS-primed fMLP-triggered oxidative burst. While Western blotting showed that 100 microM PD 98059 completely inhibited LPS-mediated ERK activation, oxidative response to fMLP by a chemiluminescence assay revealed that the same concentration inhibited the LPS-primed oxidative burst by only 40%. We conclude that in neutrophils, LPS-mediated activation of ERK 1 and 2 requires plasma and that this activation is not dependent on fibronectin. In addition, we found that the ERK pathway is not responsible for the lack of LPS priming in neutrophils of newborns but may be required for 40% of the LPS-primed fMLP-triggered oxidative burst in cells of adults.

Blockade by polyunsaturated n-3 fatty acids of endotoxin-induced monocytic tissue factor activation is mediated by the depressed receptor expression in THP-1 cells

BACKGROUND

Monocytic hypercoagulation often occurs in inflammatory conditions. We have previously reported that polyunsaturated n-3 fatty acids (n-3 FA) including eicosapentaenoic acid (20:5) and docosahexaenoic acid (22:6) prevent the activation of monocytic tissue factor (TF) induced by bacterial endotoxin [lipopolysaccharide (LPS)] in cell cultures and animals.

HYPOTHESIS

We herein explore the mode of inhibitory action of n-3 FA to determine if LPS transmembrane signaling is blocked, exerting such antagonism.

RESULTS

Exposure of human leukemia monocytic THP-1 cells to bacterial endotoxin (Escherichia coli 0111:B04, 1.5 microg/ml) for 6 h significantly activated TF activity and the production of nitric oxide (NO), tumor necrosis factor alpha (TNF-alpha), and interleukin (IL)-1beta in conditioned medium. Pretreatment with n-3 FA, 20:5 and 22:6 at 10 microM, resulted in time-dependent suppression of not only TF activation but also the elicitation of NO, TNF-alpha, and IL-1beta. These LPS responses were substantially depressed by more than 50% after a 72-h pretreatment. FACScan analysis showed that n-3 FA readily prevented fluorescein isothiocyanate (FITC)-conjugated LPS from binding to THP-1 cells by approximately 70%. The observation that anti-CD14 mAb diminished FITC-LPS binding in a dose-dependent fashion has revealed CD14 dependency in LPS recognition. LPS upregulated CD14 expression, which was significantly arrested by n-3 FA. Similarly, the upregulation of the expression of CD11b, another proposed LPS receptor, was also minimally but significantly depressed by n-3 FA.

CONCLUSION

The present study demonstrates that n-3 FA are able to block LPS transmembrane signaling via suppression of the receptor upregulation, mediating a variety of significant antagonisms against LPS action.

Neutrophil CD11b expression as a diagnostic marker for early-onset neonatal infection

OBJECTIVES

To determine whether neutrophil surface expression of CD11b predicts early-onset infection or suspected infection in at-risk infants.

STUDY DESIGN

CD11b expression on peripheral blood neutrophils was determined by flow cytometry of whole blood samples. Blood (0.1 ml) was obtained from a convenience sample of at-risk infants admitted to the neonatal intensive care unit, stained with antibodies detecting CD11b and CD15, chilled, and analyzed within 8 hours. Blood for culture, blood counts, and C-reactive protein (CRP) determination was obtained simultaneously. Subjects were grouped on the basis of culture results and clinical signs, and investigators were blinded to CD11b level.

RESULTS

Of 106 subjects, seven had positive bacterial or viral cultures ("confirmed infection"), 17 had clinical signs of infection but negative cultures ("suspected infection"), and 82 had negative cultures and no clinical signs ("no infection"). Neutrophil CD11b was elevated in all infants with confirmed infection, 94% with suspected infection, and none with no infection. The negative and positive predictive values, sensitivity, and specificity were 100%, 99%, 96%, and 100%, respectively, for diagnosis of neonatal infection at initial evaluation. CD11b levels correlated with peak CRP (r2 = 0.76, p < 0.0001); however, CD11b was elevated at the time of admission in all five infants with proven bacterial infection, whereas CRP was normal until the second day in the neonatal intensive care unit in three of these five. Both infants with positive viral cultures had elevated CD11b, but the CRP levels remained within normal limits. The negative predictive value of neutrophil CD11b for identifying suspected or confirmed infection was 99%.

CONCLUSION

This assay for neutrophil CD11b is a promising test for exclusion of early-onset neonatal infection. If validated prospectively, this assay may reduce hospital and antibiotic use in the population of neonates at risk for early-onset infection.

Reduction of acyloxyacyl hydrolase activity in circulating neutrophils from cows after parturition

Bovine neutrophils contain the enzyme acyloxyacyl hydrolase, which hydrolyzes the acyloxyacyl linkage of the two nonhydroxylated fatty acyl chains to two 3-hydroxy fatty acids in the highly conserved lipid A part of endotoxins with high specificity. This hydrolysis decreases the toxicity of lipid A, but the immunostimulatory capacity of endotoxins is largely maintained. In two trials, we studied the activity of acyloxyacyl hydrolase in neutrophils that had been isolated from the blood of 18 dairy cows around parturition. Between 10 and 26 d after parturition, the activity of acyloxyacyl hydrolase in neutrophils decreased approximately 20% below prepartum activity. At about 2 mo after parturition, acyloxyacyl hydrolase activity returned to prepartum values. Changes in acyloxyacyl hydrolase activity could not be attributed to changes in binding of lipopolysaccharides by the CD14 molecules on neutrophils or monocytes. We hypothesize that decreased acyloxyacyl hydrolase activity in neutrophils shortly after parturition is a factor that increases the susceptibility of dairy cows to coliform mastitis during early lactation.

Haematogram of the tilapiaOreochromis niloticus(Cichlidae, Teleostei) and application of a putative phenoloxidase for differentiating between neutrophilic granulocytes and monocytes

To date, little is known about the haematology of the tilapiaOreochromis niloticus, which is one of the most important species in freshwater aquaculture worldwide. We present a haematogram of O. niloticus obtained by means of panoptical staining and cytochemical procedures such as demonstration of acid phosphatase, peroxidase, oxidase, esterase, and the CD14 receptor. Emphasis was placed on the differentiation between neutrophils and monocytes, which in the past has been difficult to accomplish for many fish species. Monocytes were detected with monoclonal antibodies raised against the human CD14 receptor. Neutrophilic granulocytes displayed oxidase activity, unique for this cell type. The enzyme has many properties of a phenoloxidase. In O. niloticus this enzyme is a good marker for distinguishing neutrophils from cells of the monocyte-macrophage lineage.

Immune responses in mothers of term and preterm very-low-birth-weight infants

Differences in the levels of immune cell subsets present in peripheral blood have been demonstrated based on sociodemographic factors such as age and race. Postpartal women, who are recovering from the immune changes that are concomitant with pregnancy, have lymphocyte and monocyte values that differ from other populations. A subgroup of postpartal women, mothers who deliver preterm very-low-birth-weight (VLBW) (< or = 1,500 g) infants, may have further differences in values of immune cell subsets and in immune functioning either because of hormonal factors or lifestyle changes or because of the stress they experience after their infant's birth and for the first few months of infant caretaking. This study examined anxiety, depression, and immune cell phenotypes in 30 mothers of VLBW infants and in 30 mothers of healthy term infants over the first 4 postpartal months to determine if mothers of preterm VLBW infants differed from mothers of healthy term infants in psychological and immunologic parameters. Additionally, lymphocyte proliferation and natural killer cell functional assays were performed in a subset of mothers. Mothers of VLBW infants had increased anxiety and decreased lymphocyte proliferation compared to mothers of term infants. When lymphocyte and monocyte subsets were compared over time between the two groups of mothers differences were found in CD8, CD20, CD3-/CD56+, CD14, and HLA class II Ia on monocytes. Mothers with high-fat diets had lower percentages of some monocytes (CD14), lymphocytes (CD4+/CD45RA+), and natural killer cells (CD3-/CD57+) during the first 4 postpartal months.

Quantitative analysis of leukocyte membrane antigen expression on human fetal and cord blood: normal values and changes during development

We studied the antibody binding capacity (ABC) of various cell-surface antigens in normal human fetuses and term neonates on lymphocyte, monocyte, and polymorphonuclear (PMN) cells by quantitative flow cytometry also designated by quantimetry. Analysis of changes of expression level on these leukocytes during the developmental process was also investigated. The results indicated that the ABC values of most studied markers change during the maturational process. The ABC of lymphocyte-associated antigens studied such as CD5 and CD7 showed only a decrease from fetus to adult, whereas according to the type of molecule on monocyte and PMN there was either an increase or a decrease of ABC values dependent on the stage of the developmental process, from fetus to neonate or from neonate to adult. However, the ABC values of leukocyte membrane antigens such as CD16, CD46, and CD55 on all leukocytes and CD11b, CD11c, and CD35 on myeloid cells did not change. Their expression level was already mature in fetuses compared with adult cells. In addition, in this quantimetric approach, the analysis of the results for CD11a and CD8 suggested that the changes of CD11a expression level on lymphocyte subsets can depend on one mechanism, whereas there are probably at least two for CD8. Furthermore, the expression patterns of CD5, CD7, and CD11a change during maturation. We concluded that, even if the neonate response pattern to immunological challenge differs from an adult and this is based primarily on the relative numbers and functional activity of lymphocyte T subsets (especially TH1/TH2) and their cytokine profiles, these quantitative and qualitative phenotypical differences might also contribute to explain the functional peculiarities of leukocyte fetal and cord blood cells. All these findings support the notion of immaturity and maturity of ABC expression.

Fibronectin Enhances In Vitro Lipopolysaccharide Priming of Polymorphonuclear Leukocytes

We investigated the role of humoral factors in lipopolysaccharide (LPS) priming of polymorphonuclear leukocytes (PMN) using cells isolated from adults and from neonates. Plasma from newborn infants had decreased priming activity of adult plasma when mixed with LPS in studies measuring oxidative radical production of PMN after stimulation with a formyl bacterial oligopeptide (fMLP). This marked difference was not caused by LPS binding protein (LBP) because the LBP concentration in newborn and adult plasma were similar (138.4 ± 12.9 U for adults, and 126.9 ± 12.1 U for neonates, P = .53). Therefore, we attempted to identify other plasma factors that may contribute to LPS priming of PMN. We identified an LPS priming factor for PMN that is present in plasma, heat stable (56°C for 30 minutes), enhanced by heparin, and concentrated in cold precipitates of plasma. Because these properties resemble those of plasma fibronectin, we assessed the role of fibronectin in LPS priming of PMN. Although fibronectin in phosphate-buffered saline (PBS) had little effect on LPS priming of PMN, fibronectin in combination with other plasma factors appeared to play a role in LPS priming of PMN because (1) removing fibronectin from adult plasma dramatically decreased LPS priming activity from plasma (P < .005), (2) addition of fibronectin to fibronectin-depleted plasma restored its LPS plasma priming activity (P < .05), and (3) neutralizing fibronectin with antibody decreased the LPS priming activity of plasma (60.3 ± 1.3 v 30.2 ± 2.2, P < .01). Thus, plasma fibronectin plays a role in LPS priming of PMN in the presence of other factors in plasma.

Deficient tumor necrosis factor secretion by cord blood mononuclear cells upon in vitro stimulation with Listeria monocytogenes

We examined the production of tumor necrosis factor (TNF) by mononuclear cells (MNC) after incubating adult or cord blood MNC with Listeria monocytogenes in vitro. With adult MNC cultures, we found that TNF activity reached a peak at 6 h (606 +/- 120 x 10(3) units/liter) and declined to the baseline by day 3. In contrast, using cord blood MNC, we found that TNF activity increased gradually reaching a peak at 24 h. In addition, the peak TNF activity using newborn MNC (189 +/- 26 x 10(3) U/liter) at 24 h was still lower than the peak using adult MNC at 6 h (p < 0.0002). In seeking an explanation for the decreased TNF secretion from newborn MNC, we examined the possibility that newborn cells produce TNF but failed to secrete it. However, lysates of newborn cells contained functionally and antigenically less TNF than adult cells. Based on these observations, we conclude that the overall TNF production by newborn cells incubated with L monocytogenes is decreased compared with similarly stimulated adult cells.