Neonatal neutrophils with prolonged survival secrete mediators associated with chronic inflammation

Neutrophil responses to RSV infection show differences between infant and adult neutrophils

INTRODUCTION

Respiratory syncytial virus (RSV) causes a severe respiratory condition, bronchiolitis, in infants but not in adults. Bronchiolitis is characterised by neutrophilic infiltration in the airways, but whether neutrophils enhance recovery from infection or contribute to its pathology remains unknown.

METHODS

We used a novel in-vitro model to compare term umbilical cord blood (infant) (n=17 donors) and adult neutrophils (n=15 donors) during migration across RSV-infected differentiated human nasal airway epithelial cells (AECs) in a basolateral to apical direction.

RESULTS

Greater numbers of infant neutrophils (mean (95% CI)) (336 684 (242 352 to 431 015)) migrated across RSV-infected AECs to the apical compartment (equivalent to the airway lumen) compared with adult neutrophils (56 586 (24 954 to 88 218)) (p<0.0001). Having reached the apical compartment of infected AECs, much greater numbers of infant neutrophils (140 787 (103 117 to 178 456)) became apoptotic compared with adult (5853 (444 to 11 261)) (p=0.002). Infant neutrophils displayed much greater expression of CD11b, CD64, neutrophil elastase (NE) and myeloperoxidase (MPO) than adult neutrophils at baseline and at all points of migration. However, as adult neutrophils migrated, expression of CD11b, CD64, NE and MPO became greater than at baseline.

DISCUSSION

The high proportion of infant neutrophils migrating across RSV-infected AECs correlates with the neutrophilic infiltrate seen in infants with severe RSV bronchiolitis, with large numbers undergoing apoptosis, which may represent a protective mechanism during infection. Compared with adult neutrophils, infant neutrophils already have high expression of surface markers before contact with AECs or migration, with less capacity to increase further in response to RSV infection or migration.

Genome-wide postnatal changes in immunity following fetal inflammatory response

The fetal inflammatory response (FIR) increases the risk of perinatal brain injury, particularly in extremely low gestational age newborns (ELGANs, < 28 weeks of gestation). One of the mechanisms contributing to such a risk is a postnatal intermittent or sustained systemic inflammation (ISSI) following FIR. The link between prenatal and postnatal systemic inflammation is supported by the presence of well‐established inflammatory biomarkers in the umbilical cord and peripheral blood. However, the extent of molecular changes contributing to this association is unknown. Using RNA sequencing and mass spectrometry proteomics, we profiled the transcriptome and proteome of archived neonatal dried blood spot (DBS) specimens from 21 ELGANs. Comparing FIR‐affected and unaffected ELGANs, we identified 782 gene and 27 protein expression changes of 50% magnitude or more, and an experiment‐wide significance level below 5% false discovery rate. These expression changes confirm the robust postnatal activation of the innate immune system in FIR‐affected ELGANs and reveal for the first time an impairment of their adaptive immunity. In turn, the altered pathways provide clues about the molecular mechanisms triggering ISSI after FIR, and the onset of perinatal brain injury.

Databases

EGAS00001003635 (EGA); PXD011626 (PRIDE).

Concentrations of neutrophil-derived proteins in meconium and their correlations

AIM

The aim was to measure concentrations of four neutrophil-derived proteins in meconium as biomarkers describing prenatal environment.

METHODS

Calprotectin, lactoferrin, myeloperoxidase and PMN-elastase concentrations were measured using ELISA kits in serial meconium portions (n = 81) from 20 healthy neonates.

RESULTS

The highest concentration was for calprotectin (286.5 ± 214.6 µg/g) with a positive correlation (r = 0.75, p < 0.0001) with myeloperoxidase (1.81 ± 1.72 µg/g). For PMN-elastase (1.70 ± 2.69 µg/g) a negative correlation was observed with calprotectin and myeloperoxidase (r = -0.51, p < 0.0001; r = -0.60, p < 0.0001, respectively). Concentration of lactoferrin (45.07 ± 78.53 µg/g) correlated only with that of myeloperoxidese (r = 0.36, p = 0.0009).

CONCLUSION

Calprotectin, lactoferrin, myeloperoxidase and PMN-elastase concentrations in meconium are interrelated. These proteins may serve as objective biomarkers describing and/or assessing the intrauterine environment.

Systemic inflammation on postnatal days 21 and 28 and indicators of brain dysfunction 2years later among children born before the 28th week of gestation

BACKGROUND

Systemic inflammation during the first two postnatal weeks in extremely preterm newborns (<28weeks gestation) has been associated with an increased risk of neurodevelopmental dysfunctions. Little is known, however, about the relationship between systemic inflammation during the third and fourth postnatal weeks and subsequent development.

METHODS

We measured the concentrations of 16 inflammation-related proteins in blood spots collected on postnatal days 21 (N=749) and 28 (N=697) from infants born before the 28th week of gestation and assessed at age 2years. We then sought the developmental correlates of top quartile concentrations for gestational age and day the specimen was collected. Odds ratios and 95% confidence intervals were calculated from regular or multinomial logistic regression models (as appropriate).

RESULTS

Top quartile concentrations of CRP, IL-1β, IL-6, IL-6R, TNF-R2, IL-8, ICAM-1, and TSH on both days 21 and 28 were associated with ventriculomegaly (when in the NICU) and microcephaly at age 2years. Top quartile concentrations of CRP, SAA, IL-6, TNF-R2, IL-8, and ICAM-1 were associated with mental development index (MDI) of the Bayley-II<55, while top quartile concentrations of CRP, TNF-α (inversely), IL-8, and ICAM-1 were associated with psychomotor development index (PDI)<55 CONCLUSION: Extremely preterm newborns who had systemic inflammation during the third and fourth postnatal weeks were at increased risk of ventriculomegaly during the months after birth, and of microcephaly, and low Bayley Scale scores at 2years old.

Persistent systemic monocyte and neutrophil activation in neonatal encephalopathy

AIM

Circulating immune cell activation is associated with worse outcome in adult and animal models of brain injury. Our aim was to profile the systemic inflammatory response over the first week of life in infants at risk of neonatal encephalopathy and correlate early neutrophil and monocyte endotoxin and activation responses with outcome.

METHODS

Prospective observational study in a tertiary referral university hospital including 22 infants requiring resuscitation at birth who had serial (five time points) neutrophil and monocyte CD11b (marker of cell adhesion) (intracellular Reactive oxygen intermediates) ROI (cell activation), and Toll-like receptor (endotoxin recognition) before and after endotoxin stimulation ex vivo compared to neonatal controls.

RESULTS

All neonates requiring resuscitation at delivery (n = 122 samples) had higher neutrophil and monocyte CD11b and TLR-4 expressions compared with adults and neonatal controls. Neonates with abnormal neuroimaging and/or severe neonatal encephalopathy had increased CD11b, ROI and TLR-4. Increased PMN TLR-4 expression was associated with increased mortality in infants with neonatal encephalopathy (NE).

CONCLUSION

Innate immune dysregulation in the first week of life is associated with severity of outcome in neonatal brain injury in this cohort and may be amenable to immunomodulation.

Persistent systemic monocyte and neutrophil activation in neonatal encephalopathy

AIM

Circulating immune cell activation is associated with worse outcome in adult and animal models of brain injury. Our aim was to profile the systemic inflammatory response over the first week of life in infants at risk of neonatal encephalopathy (NE) and correlate early neutrophil and monocyte endotoxin and activation responses with outcome.

METHODS

Prospective observational study in a tertiary referral university hospital including 22 infants requiring resuscitation at birth who had serial (five time points) neutrophil and monocyte CD11b (marker of cell adhesion), intracellular reactive oxygen intermediates (ROI; cell activation) and Toll-like receptor (TLR; endotoxin recognition) before and after endotoxin stimulation ex vivo compared to neonatal controls.

RESULTS

All neonates requiring resuscitation at delivery (n = 122 samples) had higher neutrophil and monocyte CD11b and TLR-4 expression compared with adults and neonatal controls. Neonates with abnormal neuroimaging and/or severe NE had increased CD11b, ROI and TLR-4. Increased polymorphonuclear leukocytes TLR-4 expression was associated with increased mortality in infants with NE.

CONCLUSION

Innate immune dysregulation in the first week of life is associated with severity of outcome in neonatal brain injury in this cohort and may be amenable to immunomodulation.

Toll-like receptor signaling in neonatal sepsis and inflammation: a matter of orchestration and conditioning

Altered neonatal Toll-like receptor (TLR) function is hypothesized to contribute to the heightened susceptibility to infection and perpetuated inflammation in term and preterm neonates, clinically evident in neonatal sepsis and increased rates of inflammatory disorders. Current data indicate that basal TLR expression in term neonates equals adult expression patterns, while expression in preterm infants seems to increase, depending on gestational age. Regarding TLR signaling, some studies suggest TLR incompetence in neonates associated with impaired pro-inflammatory responses, others describe neonatal TLR function well developed and allude to its hyper-inflammation tendency. We discuss the competing positions and considerable limitations of research approaches and conclude that neonatal innate immunity is not generally less able to respond to TLR stimulation. Moreover, we describe pre-conditioning factors other than immaturity having a comparable impact. In the long term, better understanding of the complex interplay of pre- and postnatal conditions and maturation-dependent neonatal TLR function may provide new therapeutic approaches.

Intermittent or sustained systemic inflammation and the preterm brain

Exposure to perinatal infection and inflammation is associated with an increased risk for neonatal brain damage and developmental disabilities. In this integrated mechanism review, we discuss evidence in support of the contention that the preterm newborn is capable of intermittent or sustained systemic inflammation (ISSI), which appears to contribute more to adverse neurodevelopmental outcomes in preterm infants than does shorter duration inflammation.

Cord blood neutrophils display a galectin-3 responsive phenotype accentuated by vaginal delivery

BACKGROUND

Term neonates are at increased risk of infections due to undeveloped immune mechanisms, and proper neutrophil function is important for perinatal immune defence. Galectin-3, an endogenous β-galactoside-binding lectin, is emerging as an inflammatory mediator and we have previously shown that primed/activated, but not resting, adult neutrophils respond to this lectin by production of reactive oxygen species (ROS). We investigated if galectin-3 is of importance in perinatal immune defence, focusing on plasma levels and neutrophil responsiveness.

METHODS

Neutrophils were isolated from peripheral blood of healthy adults and cord blood (CB) after elective Caesarean section (CSCB) and vaginal delivery (VDCB). ROS production was measured by chemiluminescence, L-selectin expression by flow cytometry, and interleukin-8 (IL-8) and galectin-3 concentrations by ELISA. Statistical evaluations were performed using the Mann-Whitney test.

RESULTS

In response to galectin-3, CSCB neutrophils showed a small but clear ROS production not evident in adult cells, signifying that neonatal neutrophils exist in a primed state. IL-8 production was elevated in CSCB cells while L-selectin exposure was equal to adult cells. Comparing CSCB to VDCB neutrophils, the latter showed an extensive galectin-3 responsiveness, indicating that the degree of priming is dependent on mode of delivery. VDCB neutrophils were increasingly prone to shed L-selectin, while the amount of IL-8 was similar to CSCB cells. The endogenous galectin-3 levels were higher in neonatal as compared to adult plasma, unaffected by mode of delivery.

CONCLUSIONS

Neutrophils enter a pre-primed state already in the fetus. Upon exposure to the inflammatory stimuli that are associated with labor, the neutrophils develop a reactive phenotype with extensive priming features.

Differential effect of exogenous interleukin-10 versus glucocorticoids on gene expression and pro-inflammatory cytokine release by polymorphonuclear leukocytes and monocytes of the newly born

Bronchopulmonary dysplasia (BPD) is one of the most common causes of mortality and morbidity in neonatal intensive care units. Persistent inflammation, with an abnormal influx of polymorphonuclear leukocytes (PMNs) followed by monocytes (MONOs), occurs early in the pathogenesis of BPD. Anti-inflammatory therapy with better efficacy and safety than dexamethasone (DEX) is needed. In the present study we determined cell-specific gene expression and cytokine release in response to glucocorticoids versus interleukin-10 (IL-10). Subsequently, we hypothesized that the insensitivity of MONOs to DEX was associated with a failure of the glucocorticoid receptor to translocate to the nucleus. PMNs and MONOs were isolated from umbilical cord blood at birth, and pretreated with PBS vehicle, IL-10 or glucocorticoids prior to endotoxin (LPS)-stimulation for 4 and 18h. Genome-wide gene expressions were determined by microarray and validated by RT-qPCR. Interleukin 8 release in cell culture supernatant was measured by ELISA. To examine the mechanism of monocyte insensitivity to glucocorticoids, nuclear translocation of the glucocorticoid receptor was determined by Western blots. MONOs had 6 times the number of genes changing expression with IL-10 compared to PMNs at 4h. DEX at the therapeutic level for neonates with BPD had no effect on gene expression in MONOs. The order of potency for inhibition of interleukin-8 release from MONOs was IL-10 >betamethasone >dexamethasone and hydrocortisone. Glucocorticoid potency in MONOs was directly related to glucocorticoid receptor translocation to nucleus. Gene expression profiling for IL-10 versus glucocorticoids indicates there may be major differences in therapeutic efficacy for BPD.

Effects of bilirubin on neutrophil responses in newborn infants

BACKGROUND

Newborns are susceptible to inflammatory diseases due to defects in clearing activated immune cells from tissues. Therefore, mechanisms have likely evolved to protect neonates from leukocyte-mediated cytotoxicity. Bilirubin has antioxidant activity, and it is possible that it also exerts effects on cellular immune responses in jaundiced infants.

OBJECTIVES

We hypothesize that bilirubin increases expression of antioxidant genes and decreases production of inflammatory proteins in neonatal neutrophils.

METHODS

Neutrophils were isolated from umbilical cord blood, and from adults for comparison, and treated with bilirubin (10-300 µmol/l, equivalent to unbound bilirubin 3-40 nmol/l), in the presence or absence of lipopolysaccharide (LPS). Expression of genes for antioxidant enzymes [superoxide dismutase (SOD), heme-oxygenase-1 (HO-1)] and heme-dependent enzymes involved in inflammation [NADPH oxidase-1 (NOX-1), cyclooxygenase-2 (COX-2)] was measured by PCR. Inflammatory cytokines were measured by bead array analysis using flow cytometry.

RESULTS

We found that LPS induced production of interleukin (IL)-8, IL-1β, and macrophage inhibitory protein-1β (MIP-1β). Bilirubin increased basal production of IL-8 and IL-1β, but downregulated LPS-induced generation of IL-8 and MIP-1β. It also upregulated SOD and HO-1 gene expression. We observed an unexpected bilirubin-induced increase in gene expression of NOX-1 in LPS-activated cells, and of COX-2 in both resting and activated cells.

CONCLUSIONS

These findings suggest that bilirubin suppresses inflammation and increases antioxidant enzyme generation in activated neonatal neutrophils. The unexpected increases in NOX-1 and COX-2 expression may represent an early response, with physiologic effects mitigated by increased antioxidant activity. Further studies will be needed to define levels of bilirubin that optimize its protective effects, while minimizing potential inflammatory toxicity.

Thalidomide has anti-inflammatory properties in neonatal immune cells

Neonates demonstrate functional immaturity and dysregulation of immune responses leading to systemic inflammation and enhanced apoptosis of immune cells. Thalidomide has already been proven to differentially regulate immune responses and support anti-apoptosis in immunodeficiency syndromes. Thus, it was the aim of this study to evaluate the effects of thalidomide on the cytokine response and apoptosis of neonatal immune cells. After whole blood culture and stimulation of cord and adult blood samples, the intracytoplasmic expression and the secreted amounts of IL-2, TNF-α, IFN-γ, IL-6, IL-10 and IL-8 were assessed by flow cytometry and Cytokine Bead Array. Apoptosis was detected using Annexin-V staining. Bcl-2 expression was analysed using the Cytokine Bead Array Apoptosis Kit. Exposure to thalidomide (100 µg/ml) reduced the intracytoplasmic pro-inflammatory cytokine production of neonatal monocytes and the IFN-γ production of neonatal lymphocytes. In supernatants, the addition of thalidomide resulted in reduction of TNF-α, IL-6, IL-10 and, by trend, IFN-γ. While stimulated neonatal lymphocytes exhibited susceptibility to apoptosis, thalidomide tended to diminish apoptotic cells. Bcl-2 expression tended to be increased after addition of thalidomide. The potent anti-inflammatory effects of thalidomide and its anti-apoptotic properties in cord blood immune cells provide the basis for future strategies to optimise treatment of neonatal infections and immunodeficiency syndromes.

Toll-like receptor 1/2 stimulation induces elevated interleukin-8 secretion in polymorphonuclear leukocytes isolated from preterm and term newborn infants

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.

Flice inhibitory protein is associated with the survival of neonatal neutrophils

Neonatal polymorphonuclear leukocytes (PMN) exhibit delayed apoptosis both constitutively and under inflammatory conditions, and evidence has linked PMN longevity to the presence of antiapoptotic proteins. Activation of the survival-associated transcription factor, nuclear factor kappa B (NF-κB), promotes the synthesis of several antiapoptotic proteins including Flice inhibitory protein (FLIP). Neonatal and adult PMN were compared in this study to test the hypothesis that FLIP modulates age-related apoptosis. Expression of the short isoform, FLIP-S, was prominent at baseline and persisted during spontaneous apoptosis in neonatal PMN, whereas basal expression was lower and decreased under the same conditions in adult PMN. Stable FLIP-S expression in neonatal PMN was associated with a relative resistance to apoptosis in response to the protein synthesis inhibitor, cycloheximide (CHX), or the NF-κB inhibitor, gliotoxin. In contrast, similar treatment of adult PMN promoted greater overall apoptosis accompanied by FLIP degradation. Nuclear levels of phosphorylated p65, a critical NF-κB dimer, were relatively robust in neonatal PMN under basal conditions or after stimulation with TNF-α, a cytokine that induces FLIP. In conclusion, persistent FLIP-S expression is involved in the longevity of neonatal PMN, and our data suggest a contribution of NF-κB signaling and related survival mechanisms.