Potential of immunomodulatory agents for prevention and treatment of neonatal sepsis

Development and validation of a novel risk classification tool for predicting long length of stay in NICU blood transfusion infants

Newborns are as the primary recipients of blood transfusions. There is a possibility of an association between blood transfusion and unfavorable outcomes. Such complications not only imperil the lives of newborns but also cause long hospitalization. Our objective is to explore the predictor variables that may lead to extended hospital stays in neonatal intensive care unit (NICU) patients who have undergone blood transfusions and develop a predictive nomogram. A retrospective review of 539 neonates who underwent blood transfusion was conducted using median and interquartile ranges to describe their length of stay (LOS). Neonates with LOS above the 75th percentile (P75) were categorized as having a long LOS. The Least Absolute Shrinkage and Selection Operator (LASSO) regression method was employed to screen variables and construct a risk model for long LOS. A multiple logistic regression prediction model was then constructed using the selected variables from the LASSO regression model. The significance of the prediction model was evaluated by calculating the area under the ROC curve (AUC) and assessing the confidence interval around the AUC. The calibration curve is used to further validate the model's calibration and predictability. The model's clinical effectiveness was assessed through decision curve analysis. To evaluate the generalizability of the model, fivefold cross-validation was employed. Internal validation of the models was performed using bootstrap validation. Among the 539 infants who received blood transfusions, 398 infants (P75) had a length of stay (LOS) within the normal range of 34 days, according to the interquartile range. However, 141 infants (P75) experienced long LOS beyond the normal range. The predictive model included six variables: gestational age (GA) (< 28 weeks), birth weight (BW) (< 1000 g), type of respiratory support, umbilical venous catheter (UVC), sepsis, and resuscitation frequency. The area under the receiver operating characteristic (ROC) curve (AUC) for the training set was 0.851 (95% CI 0.805-0.891), and for the validation set, it was 0.859 (95% CI 0.789-0.920). Fivefold cross-validation indicates that the model has good generalization ability. The calibration curve demonstrated a strong correlation between the predicted risk and the observed actual risk, indicating good consistency. When the intervention threshold was set at 2%, the decision curve analysis indicated that the model had greater clinical utility. The results of our study have led to the development of a novel nomogram that can assist clinicians in predicting the probability of long hospitalization in blood transfused infants with reasonable accuracy. Our findings indicate that GA (< 28 weeks), BW(< 1000 g), type of respiratory support, UVC, sepsis, and resuscitation frequency are associated with a higher likelihood of extended hospital stays among newborns who have received blood transfusions.

Sex differences in neonatal brain injury and inflammation

Neonatal brain injury and associated inflammation is more common in males. There is a well-recognised difference in incidence and outcome of neonatal encephalopathy according to sex with a pronounced male disadvantage. Neurodevelopmental differences manifest from an early age in infancy with females having a lower incidence of developmental delay and learning difficulties in comparison with males and male sex has consistently been identified as a risk factor for cerebral palsy in epidemiological studies. Important neurobiological differences exist between the sexes with respect to neuronal injury which are especially pronounced in preterm neonates. There are many potential reasons for these sex differences including genetic, immunological and hormonal differences but there are limited studies of neonatal immune response. Animal models with induced neonatal hypoxia have shown various sex differences including an upregulated immune response and increased microglial activation in males. Male sex is recognized to be a risk factor for neonatal hypoxic ischemic encephalopathy (HIE) during the perinatal period and this review discusses in detail the sex differences in brain injury in preterm and term neonates and some of the potential new therapies with possible sex affects.

Predictors of extubation failure in newborns: a systematic review and meta-analysis

Extubation failure (EF) is a significant concern in mechanically ventilated newborns, and predicting its occurrence is an ongoing area of research. To investigate the predictors of EF in newborns undergoing planned extubation, we conducted a systematic review and meta-analysis. A systematic literature search was conducted in PubMed, Web of Science, Embase, and Cochrane Library for studies published in English from the inception of each database to March 2023. The PRISMA guidelines were followed in all phases of this systematic review. The Risk of Bias Assessment for Nonrandomized Studies tool was used to assess methodological quality. Thirty-four studies were included, 10 of which were overall low risk of bias, 15 of moderate risk of bias, and 9 of high risk of bias. The studies reported 43 possible predictors in six broad categories (intrinsic factors; maternal factors; diseases and adverse conditions of the newborn; treatment of the newborn; characteristics before and after extubation; and clinical scores and composite indicators). Through a qualitative synthesis of 43 predictors and a quantitative meta-analysis of 19 factors, we identified five definite factors, eight possible factors, and 22 unclear factors related to EF. Definite factors included gestational age, sepsis, pre-extubation pH, pre-extubation FiO2, and respiratory severity score. Possible factors included age at extubation, anemia, inotropic use, mean airway pressure, pre-extubation PCO2, mechanical ventilation duration, Apgar score, and spontaneous breathing trial. With only a few high-quality studies currently available, well-designed and more extensive prospective studies investigating the predictors affecting EF are still needed. In the future, it will be important to explore the possibility of combining multiple predictors or assessment tools to enhance the accuracy of predicting extubation outcomes in clinical practice.

Risk factors for length of NICU stay of newborns: A systematic review

Background

The improvement in survival of preterm infants is accompanied by an increase in neonatal intensive care unit (NICU) admissions. Prolonged length of stay in the NICU (LOS-NICU) increases the incidence of neonatal complications and even mortality and places a significant economic burden on families and strain on healthcare systems. This review aims to identify risk factors influencing LOS-NICU of newborns and to provide a basis for interventions to shorten LOS-NICU and avoid prolonged LOS-NICU.

Methods

A systematic literature search was conducted in PubMed, Web of Science, Embase, and Cochrane library for studies that were published in English from January 1994 to October 2022. The PRISMA guidelines were followed in all phases of this systematic review. The Quality in Prognostic Studies (QUIPS) tool was used to assess methodological quality.

Results

Twenty-three studies were included, 5 of which were of high quality and 18 of moderate quality, with no low-quality literature. The studies reported 58 possible risk factors in six broad categories (inherent factors; antenatal treatment and maternal factors; diseases and adverse conditions of the newborn; treatment of the newborn; clinical scores and laboratory indicators; organizational factors).

Conclusions

We identified several of the most critical risk factors affecting LOS-NICU, including birth weight, gestational age, sepsis, necrotizing enterocolitis, bronchopulmonary dysplasia, and retinopathy of prematurity. As only a few high-quality studies are available at present, well-designed and more extensive prospective studies investigating the risk factors affecting LOS-NICU are still needed in the future.

Clinical impact of NEC-associated sepsis on outcomes in preterm infants

OBJECTIVE

To determine risk factors and outcomes of necrotizing enterocolitis (NEC)-associated sepsis in infants with NEC.

METHODS

A retrospective review comparing demographic and clinical information in infants with and without NEC-associated sepsis (defined as positive blood culture at the time of NEC onset).

RESULTS

A total of 209 infants with medical (n = 98) and surgical NEC (n = 111) had a median gestational age of 27 weeks (IQR 25; 30.5) and a median birth weight of 910 g [IQR 655; 1138]. Fifty of 209 (23.9%) infants had NEC-associated sepsis. Infants with NEC-associated sepsis had lower median GA (26.4 vs. 27.4 weeks; p = 0.01), lower birth weight (745 vs. 930 g; p = 0.009), were more likely mechanically ventilated [p < 0.001], received dopamine [p < 0.001], had more evidence of acute kidney injury [60% vs. 38.4%, p = 0.01], longer postoperative ileus (16 [13.0; 22.0] vs. 12 [8; 16] days; p = 0.006), higher levels of C-reactive protein, lower platelet counts, longer hospitalization compared to infants without NEC-associated sepsis. On multivariate regression, cholestasis was an independent risk factor for NEC-associated sepsis (OR 2.94; 95% CI 1.1-8.8, p = 0.038).

CONCLUSION

NEC-associated sepsis was associated with greater hemodynamic support, acute kidney injury, longer postoperative ileus, and hospitalization on bivariate analysis, and cholestasis was associated with higher odds of sepsis on multi regression analysis.

IMPACT

NEC-associated sepsis was present in 24% of infants with NEC. Gram-positive bacteria, Gram-negative bacteria, and Candida were found in 15.3%, 10.5%, and 2.8% of cases, respectively. Infants with NEC-associated sepsis had a greater inflammatory response (CRP levels), received more blood transfusion before NEC onset, frequently needed assisted ventilation ionotropic support, and had acute kidney injury after NEC onset. NEC infants with Gram-negative sepsis had higher portal venous gas, received more platelet transfusions before NEC onset, and had higher CRP levels and lower median lymphocyte counts at 24 h after NEC onset than those with Gram-positive sepsis.

Reelin cells and sex-dependent synaptopathology in autism following postnatal immune activation

BACKGROUND AND PURPOSE

Autism spectrum disorders (ASD) are heterogeneous neurodevelopmental disorders with considerably increased risk in male infants born preterm and with neonatal infection. Here, we investigated the role of postnatal immune activation on hippocampal synaptopathology by targeting Reelin+ cells in mice with ASD-like behaviours.

EXPERIMENTAL APPROACH

C57/Bl6 mouse pups of both sexes received lipopolysaccharide (LPS, 1 mg·kg-1 ) on postnatal day (P) 5. At P45, animal behaviour was examined by marble burying and sociability test, followed by ex vivo brain MRI diffusion kurtosis imaging (DKI). Hippocampal synaptogenesis, number and morphology of Reelin+ cells, and mRNA expression of trans-synaptic genes, including neurexin-3, neuroligin-1, and cell-adhesion molecule nectin-1, were analysed at P12 and P45.

KEY RESULTS

Social withdrawal and increased stereotypic activities in males were related to increased mean diffusivity on MRI-DKI and overgrowth in hippocampus together with retention of long-thin immature synapses on apical dendrites, decreased volume and number of Reelin+ cells as well as reduced expression of trans-synaptic and cell-adhesion molecules.

CONCLUSION AND IMPLICATIONS

The study provides new insights into sex-dependent mechanisms that may underlie ASD-like behaviour in males following postnatal immune activation. We identify GABAergic interneurons as core components of dysmaturation of excitatory synapses in the hippocampus following postnatal infection and provide cellular and molecular substrates for the MRI findings with translational value.

Knowledge gaps in late-onset neonatal sepsis in preterm neonates: a roadmap for future research

Late-onset neonatal sepsis (LONS) remains an important threat to the health of preterm neonates in the neonatal intensive care unit. Strategies to optimize care for preterm neonates with LONS are likely to improve survival and long-term neurocognitive outcomes. However, many important questions on how to improve the prevention, early detection, and therapy for LONS in preterm neonates remain unanswered. This review identifies important knowledge gaps in the management of LONS and describe possible methods and technologies that can be used to resolve these knowledge gaps. The availability of computational medicine and hypothesis-free-omics approaches give way to building bedside feedback tools to guide clinicians in personalized management of LONS. Despite advances in technology, implementation in clinical practice is largely lacking although such tools would help clinicians to optimize many aspects of the management of LONS. We outline which steps are needed to get possible research findings implemented on the neonatal intensive care unit and provide a roadmap for future research initiatives. IMPACT: This review identifies knowledge gaps in prevention, early detection, antibiotic, and additional therapy of late-onset neonatal sepsis in preterm neonates and provides a roadmap for future research efforts. Research opportunities are addressed, which could provide the means to fill knowledge gaps and the steps that need to be made before possible clinical use. Methods to personalize medicine and technologies feasible for bedside clinical use are described.

Protective Role of an Initial Low-Dose Septic Challenge against Lethal Sepsis in Neonatal Mice: A Pilot Study

Neonatal sepsis is characterized by systemic bacterial invasion followed by a massive inflammatory response. At present, no therapeutic strategy has been found that significantly reduces the mortality of neonatal sepsis. We aimed to investigate the protective role of an initial low-dose septic challenge for the prevention of subsequent lethal sepsis in a mouse model. A stock cecal slurry (CS) solution was prepared from adult ceca. The LD83 (1.5 mg CS/g) was used for all animals. An initial challenge of normal saline (NS) or 0.5 mg CS/g (non-lethal dose) was administered at four days of age, then 1.5 mg CS/g was administered intraperitoneally at seven days of age (72 h post-initial challenge), and survival was monitored. Initial exposure to NS (n = 10) resulted in 90% mortality following exposure to the LD83 CS dose in contrast to an initial exposure to CS (n = 16), which significantly decreased mortality to 6% (p < 0.0001), reduced blood bacterial counts, attenuated inflammatory responses, and suppressed lipid mediators. Initial exposure to a non-lethal CS dose prior to exposure to a lethal CS dose significantly reduces sepsis mortality, a protective effect that might be mediated by modulating abnormal systemic inflammatory responses.

Comparison of Interleukin-6 Plasma Concentration in Multisystem Inflammatory Syndrome in Children Associated With SARS-CoV-2 and Pediatric Sepsis

Importance: Multisystem Inflammatory Syndrome in Children (MIS-C) associated with SARS-CoV-2 infection is thought to be driven by a post-viral dysregulated immune response, where interleukin 6 (IL-6) might have a central role. In this setting, IL-6 inhibitors are prescribed as immunomodulation in cases refractory to standard therapy. Objective: To compare plasma IL-6 concentration between critically ill children with MIS-C and sepsis. Design: A retrospective cohort study from previously collected data. Setting: Individual patient data were gathered from three different international datasets. Participants: Critically ill children between 1 month-old and 18 years old, with an IL-6 level measured within 48 h of admission to intensive care. Septic patients were diagnosed according to Surviving Sepsis Campaign definition and MIS-C cases by CDC criteria. We excluded children with immunodeficiency or immunosuppressive therapy. Exposure: None. Main Outcome(s) and Measure(s): The primary outcome was IL-6 plasma concentration in MIS-C and sepsis group at admission to the intensive care unit. We described demographics, inflammatory biomarkers, and clinical outcomes for both groups. A subgroup analysis for shock in each group was done. Results: We analyzed 66 patients with MIS-C and 44 patients with sepsis. MIS-C cases were older [96 (48, 144) vs. 20 (5, 132) months old, p < 0.01], but no differences in sex (41 vs. 43% female, p = 0.8) compared to septic group. Mechanical ventilation use was 48.5 vs. 93% (p < 0.001), vasoactive drug use 79 vs. 66% (p = 0.13), and mortality 4.6 vs. 34.1% (p < 0.01) in MIS-C group compared to sepsis. IL-6 was 156 (36, 579) ng/dl in MIS-C and 1,432 (122, 6,886) ng/dl in sepsis (p < 0.01), while no significant differences were observed in procalcitonin (PCT) and c-reactive protein (CRP). 52/66 (78.8%) patients had shock in MIS-C group, and 29/44 (65.9%) had septic shock in sepsis group. Septic shock had a significantly higher plasma IL-6 concentration than the three other sub-groups. Differences in IL-6, CRP, and PCT were not statistically different between MIS-C with and without shock. Conclusions and Relevance: IL-6 plasma concentration was elevated in critically ill MIS-C patients but at levels much lower than those of sepsis. Furthermore, IL-6 levels don't discriminate between MIS-C cases with and without shock. These results lead us to question the role of IL-6 in the pathobiology of MIS-C, its diagnosis, clinical outcomes, and, more importantly, the off-label use of IL-6 inhibitors for these cases.

Exploring Clinically-Relevant Experimental Models of Neonatal Shock and Necrotizing Enterocolitis

Neonatal shock and necrotizing enterocolitis (NEC) are leading causes of morbidity and mortality in premature infants. NEC is a life-threatening gastrointestinal illness, the precise etiology of which is not well understood, but is characterized by an immaturity of the intestinal barrier, altered function of the adaptive immune system, and intestinal dysbiosis. The complexities of NEC and shock in the neonatal population necessitate relevant clinical modeling using newborn animals that mimic the disease in human neonates to better elucidate the pathogenesis and provide an opportunity for the discovery of potential therapeutics. A wide variety of animal species-including rats, mice, piglets, and primates-have been used in developing experimental models of neonatal diseases such as NEC and shock. This review aims to highlight the immunologic differences in neonates compared with adults and provide an assessment of the advantages and drawbacks of established animal models of both NEC and shock using enteral or intraperitoneal induction of bacterial pathogens. The selection of a model has benefits unique to each type of animal species and provides individual opportunities for the development of targeted therapies. This review discusses the clinical and physiologic relevance of animal models and the insight they contribute to the complexities of the specific neonatal diseases: NEC and shock.

Cumulative evidence for association of sepsis and retinopathy of prematurity

BACKGROUND

Retinopathy of prematurity (ROP) is a retinal vasoproliferative disease affected by multiple factors such as infection and preterm birth. The role of sepsis in the development of ROP remains controversial. This systematic review and meta-analysis aimed to identify the impact of sepsis on ROP.

METHODS

The PubMed, Embase, and Cochrane Library databases were searched using terms related to sepsis and ROP. Cohort or case-control studies that reported the association of sepsis and ROP were eligible. The odds ratios (ORs) together with the 95% confidence interval (CI) were extracted from the studies or computed by authors if not provided.

RESULTS

Thirty-four studies were ultimately included in this meta-analysis. The pooled results showed that sepsis increased the risk for the development of any stage ROP (OR = 2.16; 95% CI: 1.65-2.82). Both early onset (OR = 2.50; 95% CI: 1.97-3.18) and late-onset (OR = 1.37; 95% CI: 1.22-1.55) sepsis were associated with severe ROP. Furthermore, both bacterial sepsis (OR = 1.74; 95% CI: 1.21-2.50) and fungal sepsis (OR = 2.96; 95% CI: 2.05-4.28) were also found to be associated with severe ROP.

CONCLUSION

Sepsis increased the risk of any stage ROP, especially for the severe ROP. Further high-quality clinical studies are needed to eliminate heterogeneity and publication bias to validate these findings.

Hospital-acquired Enterobacteriaceae bloodstream infections in children

Among the different age groups of children, newborns are most exposed to hospital-acquired bloodstream infection (HA-BSI), especially those who are burdened with additional risk factors, such as low birth weight, immaturity or exposition to medical procedures. The aim of this study was to analyze the aetiology of HA-BSI among children at high risk, including incidence and drug resistance. The data was obtained from the PubMed database and included medical articles as well as UNICEF and WHO reports published from 2002 to 2017. The study focused on newborns and older children (under 18 years old) with BSI. The main eligibility criteria, apart from age, were Enterobacteriaceae HA-BSI, and the use of invasive medical procedures. It was demonstrated that the main risk factors of infection were age and medical procedures. Due to non-specific symptoms, sepsis is difficult to diagnose, a fact which leads to a high mortality rate in newborns. The existence of such multi-drug resistant strains as Extended-Spectrum β-Lactamases (ESBLs) or Carbapenem-Resistant Enterobacteriaceae (CRE) phenotypes is a grave cause for concern.

Enhancement of immune response mediated by oropharyngeal colostrum administration in preterm neonates

BACKGROUND

The immune system of preterm infants is immature, being a significant cause of morbidity and mortality, particularly in the preterm infant. Oropharyngeal colostrum administration could be an immunomodulatory aid. Our aim was to evaluate the effect of oropharyngeal colostrum on the serum levels of immunoglobulins, lactoferrin, and resistin during the first month of life and to track the clinical outcome of the neonates.

METHODS

One hundred preterm neonates born at <32 weeks of gestation and/or weighing < 1500 g and assisted in the Neonatal Intensive Care Unit were enrolled and divided into two groups: colostrum (n = 48) and control (n = 52). The subjects assigned to the colostrum group received 0.2 mL of colostrum (oropharyngeal route) every 4 hours for the first 15 days of life, and if mothers have inability to breastfeed, they were included in the control group (no oropharyngeal colostrum). Serum concentrations of IgA, IgM, and IgG1, lactoferrin, and resistin were assessed in both groups at 1, 3, 15, and 30 days of life. Clinical data during hospitalization were collected.

RESULTS

IgA and IgM increased in preterm neonates who were administered colostrum for 15 and 30 days. Lactoferrin increased after 30 days, and resistin increased after 15 days of supplying oropharyngeal colostrum. The colostrum group underwent full enteral nutrition before, and no differences were observed in the common neonatal morbidities.

CONCLUSION

Oropharyngeal colostrum administration is safe in preterm neonates and improves their immunologic profile, showing a potential role as an immunomodulatory agent.

Use of C-reactive protein to tailor antibiotic use: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVES

C-reactive protein (CRP) has been proposed to guide the use of antibiotics. However, study results are controversial regarding the benefits of such a strategy. We synthesised the evidence of CRP-based algorithms on antibiotic treatment initiation and on antibiotic treatment duration in adults, children and neonates, as well as their safety profile.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

MEDLINE, EMBASE, CENTRAL and CINAHL from inception to 20 July 2017.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

We included randomised controlled trials (RCTs), non-RCTs and cohort studies (prospective or retrospective) investigating CRP-guided antibiotic use in adults, children and neonates with bacterial infection.

DATA EXTRACTION AND SYNTHESIS

Two researchers independently screened all identified studies and retrieved the data. Outcomes were duration of antibiotic use, antibiotic initiation, mortality, infection relapse and hospitalisation. We assessed the quality of the included studies using the Cochrane Collaboration's tool (RCTs), and A Cochrane Risk Of Bias Assessment Tool: for Non-Randomized Studies of Interventions and the Newcastle-Ottawa scale (non-RCTs). We analysed our results using descriptive statistics and random effects models.

RESULTS

Of 11 165 studies screened, 15 were included. In five RCTs in adult outpatients, the risk difference for antibiotic treatment initiation in the CRP group was -7% (95% CI: -10% to -4%), with no difference in hospitalisation rate. In neonates, CRP-based algorithms shortened antibiotic treatment duration by -1.45 days (95% CI -2.61 to -0.28) in two RCTs, and by -1.15 days (95% CI -2.06 to -0.24) in two cohort studies, with no differences in mortality or infection relapse.

CONCLUSION

The use of CRP-based algorithms seems to reduce antibiotic treatment duration in neonates, as well as to decrease antibiotic treatment initiation in adult outpatients. However, further high-quality studies are still needed to assess safety, particularly in children outside the neonatal period.

PROSPERO REGISTRATION NUMBER

CRD42016038622.

Beyond sepsis: Staphylococcus epidermidis is an underestimated but significant contributor to neonatal morbidity

Staphylococcus epidermidis accounts for the majority of cases of neonatal sepsis. Moreover, it has been demonstrated to be associated with neonatal morbidities, such as bronchopulmonary dysplasia (BPD), white matter injury (WMI), necrotizing enterocolitis (NEC) and retinopathy of prematurity (ROP), which affect short-term and long-term neonatal outcome. Imbalanced inflammation has been considered to be a major underlying mechanism of each entity. Conventionally regarded as a harmless commensal on human skin, S. epidermidis has received less attention than its more virulent relative Staphylococcus aureus. Particularities of neonatal innate immunity and nosocomial environmental factors, however, may contribute to the emergence of S. epidermidis as a significant nosocomial pathogen. Neonatal host response to S. epidermidis sepsis has not been fully elucidated. Evidence is emerging regarding the implication of S. epidermidis sepsis in the pathogenesis of neonatal inflammatory diseases. This review focuses on the interplay among S. epidermidis, neonatal innate immunity and inflammation-driven organ injury.

Energy Demands of Early Life Drive a Disease Tolerant Phenotype and Dictate Outcome in Neonatal Bacterial Sepsis

Bacterial sepsis is one of the leading causes of death in newborns. In the face of growing antibiotic resistance, it is crucial to understand the pathology behind the disease in order to develop effective interventions. Neonatal susceptibility to sepsis can no longer be attributed to simple immune immaturity in the face of mounting evidence that the neonatal immune system is tightly regulated and well controlled. The neonatal immune response is consistent with a "disease tolerance" defense strategy (minimizing harm from immunopathology) whereas adults tend toward a "disease resistance" strategy (minimizing harm from pathogens). One major advantage of disease tolerance is that is less energetically demanding than disease resistance, consistent with the energetic limitations of early life. Immune effector cells enacting disease resistance responses switch to aerobic glycolysis upon TLR stimulation and require steady glycolytic flux to maintain the inflammatory phenotype. Rapid and intense upregulation of glucose uptake by immune cells necessitates an increased reliance on fatty acid metabolism to (a) fuel vital tissue function and (b) produce immunoregulatory intermediates which help control the magnitude of inflammation. Increasing disease resistance requires more energy: while adults have fat and protein stores to catabolize, neonates must reallocate resources away from critical growth and development. This understanding of sepsis pathology helps to explain many of the differences between neonatal and adult immune responses. Taking into account the central role of metabolism in the host response to infection and the severe metabolic demands of early life, it emerges that the striking clinical susceptibility to bacterial infection of the newborn is at its core a problem of metabolism. The evidence supporting this novel hypothesis, which has profound implications for interventions, is presented in this review.

Marked elevation of circulating CD19+CD38hiCD24hi transitional B cells give protection against neonatal sepsis

BACKGROUND

Adequate functions of immunoregulation, mediated by regulatory cells such as IL-10 producing CD19⁺CD38^hiCD24^hi transitional B cells (Trans), play an important role in control of excessive inflammatory response. Yet, the role of Trans in neonatal sepsis is incompletely understood. We investigated the role of Trans in late-onset sepsis (LOS).

METHODS

We used multicolor flow cytometry to analyse the phenotypes of B cells drawn from a cohort of 16 neonatal late-onset sepsis (LOS) (12 survivors and 4 non-survivors) and 20 healthy neonates over time.

RESULTS

Patients undergone a serious decline of lymphocytes at the beginning of sepsis and then noticeable elevation during one week of follow-up had a good prognosis. Intriguingly, peripheral blood B cells, especially Trans, were the marked increase lymphocyte subset and maintained a high level of producing IL-10 during the 7 days of follow-up.

CONCLUSION

The level of IL-10 producing Trans was significantly elevated in peripheral blood of good prognosis newborns with LOS and might contribute to the successful immunoprotective state of the disease.

Outgrowing the Immaturity Myth: The Cost of Defending From Neonatal Infectious Disease

Newborns suffer high rates of mortality due to infectious disease-this has been generally regarded to be the result of an "immature" immune system with a diminished disease-fighting capacity. However, the immaturity dogma fails to explain (i) greater pro-inflammatory responses than adults in vivo and (ii) the ability of neonates to survive a significantly higher blood pathogen burden than of adults. To reconcile the apparent contradiction of clinical susceptibility to disease and the host immune response findings when contrasting newborn to adult, it will be essential to capture the entirety of available host-defense strategies at the newborn's disposal. Adults focus heavily on the disease resistance approach: pathogen reduction and elimination. Newborn hyperactive innate immunity, sensitivity to immunopathology, and the energetic requirements of growth and development (immune and energy costs), however, preclude them from having an adult-like resistance response. Instead, newborns also may avail themselves of disease tolerance (minimizing immunopathology without reducing pathogen load), as a disease tolerance approach provides a counterbalance to the dangers of a heightened innate immunity and has lower-associated immune costs. Further, disease tolerance allows for the establishment of a commensal bacterial community without mounting an unnecessarily dangerous immune resistance response. Since disease tolerance has its own associated costs (immune suppression leading to unchecked pathogen proliferation), it is the maintenance of homeostasis between disease tolerance and disease resistance that is critical to safe and effective defense against infections in early life. This paradigm is consistent with nearly all of the existing evidence.

Activation of Invariant Natural Killer T Cells Redirects the Inflammatory Response in Neonatal Sepsis

Sepsis is the third leading cause of death in the neonatal population, due to susceptibility to infection conferred by immaturity of both the innate and adaptive components of the immune system. Invariant natural killer T (iNKT) cells are specialized adaptive immune cells that possess important innate-like characteristics and have not yet been well-studied in septic neonates. We hypothesized that iNKT cells would play an important role in mediating the neonatal immune response to sepsis. To study this, we subjected 5- to 7-day-old neonatal C57BL/6 mice to sepsis by intraperitoneal (i.p.) cecal slurry (CS) injection. Thirty hours prior to or immediately following sepsis induction, pups received i.p. injection of the iNKT stimulator KRN7000 (KRN, 0.2 µg/g) or vehicle. Ten hours after CS injection, blood and tissues were collected for various analyses. Thirty-hour pretreatment with KRN resulted in better outcomes in inflammation, lung injury, and survival, while immediate treatment with KRN resulted in worse outcomes compared to vehicle treatment. We further analyzed the activation status of neonatal iNKT cells for 30 h after KRN administration, and showed a peak in frequency of CD69 expression on iNKT cells and serum IFN-γ levels at 5 and 10 h, respectively. We then used CD1d knockout neonatal mice to demonstrate that KRN acts through the major histocompatibility complex-like molecule CD1d to improve outcomes in neonatal sepsis. Finally, we identified that KRN pretreatment exerts its protective effect by increasing systemic levels of TGF-β1. These findings support the importance of iNKT cells for prophylactic immunomodulation in neonates susceptible to sepsis.

Neonatal intestinal dysbiosis in necrotizing enterocolitis

Necrotizing Enterocolitis (NEC) is one of the most devastating gastrointestinal diseases in neonates, particularly among preterm infants in whom surgical NEC is the leading cause of morbidity. NEC pathophysiology occurs in the hyper-reactive milieu of the premature gut after bacterial colonization. The resultant activation of the TLR4 pathway appears to be a strongly contributing factor. Advancements in metagenomics may yield new clarity to the relationship between the neonatal intestinal microbiome and the development of NEC. After a century without effective directed treatments, microbiome manipulation offers a promising therapeutic target for the prevention and treatment of this devastating disease.

They Are What You Eat: Can Nutritional Factors during Gestation and Early Infancy Modulate the Neonatal Immune Response?

The ontogeny of the human immune system is sensitive to nutrition even in the very early embryo, with both deficiency and excess of macro- and micronutrients being potentially detrimental. Neonates are particularly vulnerable to infectious disease due to the immaturity of the immune system and modulation of nutritional immunity may play a role in this sensitivity. This review examines whether nutrition around the time of conception, throughout pregnancy, and in early neonatal life may impact on the developing infant immune system.

Newborn susceptibility to infection vs. disease depends on complex in vivo interactions of host and pathogen

The burden of newborn infectious disease has long been recognized as the highest across the entire human life span. The precise underlying cause is unfortunately still far from clear. A substantial body of data derived mostly from in vitro experimentation indicates "lower" host immune responses in early vs. adult life and is briefly summarized within this review. However, emerging data derived mostly from in vivo experimentation reveal that the newborn host also exhibits an exuberant immune and inflammatory response following infection when compared to the adult. In this context, it is important to emphasize that "infection" does not equate "infectious disease," as for many infections it is the host response to the infection that causes disease. This simple insight readily arranges existing evidence into cause-effect relationships that explain much of the increase in clinical suffering from infection in early life. We here briefly summarize the evidence in support of this paradigm and highlight the important implications it has for efforts to ameliorate the suffering and dying from infection in early life.

Toll-like receptor mediated activation is possibly involved in immunoregulating properties of cow's milk hydrolysates

Immunomodulating proteins and peptides are formed during the hydrolysis of cow’s milk proteins. These proteins are potential ingredients in functional foods used for the management of a range of immune related problems, both in infants and adults. However, the mechanism behind these effects is unknown. We hypothesize that the interaction of peptides with Toll-like receptors (TLRs) can induce immune effects, since these receptors are known to sample many dietary molecules in the intestine in order to regulate immune effects. To investigate this, we compared the immune effects and TLR activation and inhibition by whey and casein hydrolysates with different hydrolysis levels. We first measured cytokine production in primary peripheral blood mononuclear cells stimulated with either whey, casein, or their hydrolysates. IL-10 and TNFα were induced by whey hydrolysates (decreasing with increasing hydrolysis level), but not by casein hydrolysates. Next, the activation of TLR 2, 3, 5 and 9 receptors were observed by intact and mildly hydrolysed whey proteins only and not by casein hydrolysates in TLR reporter cell lines. Many casein hydrolysates inhibited TLR signaling (mainly TLR 5 and 9). These results demonstrate that the effects of cow’s milk proteins on the immune system are protein type and hydrolysis dependent. TLR signaling is suggested as a possible mechanism for differences in effect. This knowledge contributes to a better understanding of the immune effects of hydrolysates and the design of infant formula, and nutrition in general, with specific immunoregulatory effects.

Timing of Multiorgan Dysfunction among Hospitalized Infants with Fatal Fulminant Sepsis

Objective Identify the progression of specific signs of multiorgan dysfunction among infants with fatal sepsis. Study Design Cohort study of 679 infants who died within 3 days of the start of a late-onset sepsis (LOS) episode in neonatal intensive care units from 1997 to 2012. We extracted clinical and laboratory data on the day of death (day 0) and the preceding 5 days (days -5 to -1). Results Median (25th percentile-75th percentile) gestational age was 25 (24-28) weeks. Compared with day -1, day 0 was characterized by an increased requirement for mechanical ventilation and higher mean fraction of inspired oxygen. Measures of cardiorespiratory support and the proportion of infants with neutropenia began to rise on day -2. Conclusion Hospitalized infants with fatal LOS manifest respiratory, cardiovascular, renal, immune, and hematologic dysfunction. Knowledge of these factors and their timing may be important for the development and testing of novel therapeutics to reduce sepsis mortality.

Age-dependent cellular reactions of the human immune system of humanized NOD scid gamma mice on LPS stimulus

Despite sepsis being a life-threatening disease, targeted drugs that improve the therapy of affected patients are still lacking. Infants and adults differ in the maturity level of their immune system and this results in distinct reactions to Gram-negative bacteria. To study reactions of human immune cells in vivo, we used NOD scid gamma mice transplanted with human CD34⁺ stem cells to engraft a functional human immune system. Human cells undergo differentiation and maturation in these mice after transplantation and, accordingly, animals were divided into two groups: 8-13 wk and 15-22 wk after transplantation. Endotoxemia was induced by injecting LPS. Six h later, mice were euthanized. In both groups, LPS stimulation induced a decrease of CD14⁺ monocytes in peripheral blood, an up-regulation of activation markers on different cell subsets such as myeloid dendritic cells, and a release of the human cytokines TNF-α, IL-6 and IL-10. However, significant differences were detected with regard to the amounts of released cytokines, and 8-13-wk-old mice produced more IL-6, while PTX3 was mainly released by 15-22-wk-old animals. Thus, here we provide a potential model for preclinical research of sepsis in infants and adults.

Immunological Defects in Neonatal Sepsis and Potential Therapeutic Approaches

Despite advances in critical care medicine, neonatal sepsis remains a major cause of morbidity and mortality worldwide, with the greatest risk affecting very low birth weight, preterm neonates. The presentation of neonatal sepsis varies markedly from its presentation in adults, and there is no clear consensus definition of neonatal sepsis. Previous work has demonstrated that when neonates become septic, death can occur rapidly over a matter of hours or days and is generally associated with inflammation, organ injury, and respiratory failure. Studies of the transcriptomic response by neonates to infection and sepsis have led to unique insights into the early proinflammatory and host protective responses to sepsis. Paradoxically, this early inflammatory response in neonates, although lethal, is clearly less robust relative to children and adults. Similarly, the expression of genes involved in host protective immunity, particularly neutrophil function, is also markedly deficient. As a result, neonates have both a diminished inflammatory and protective immune response to infection which may explain their increased risk to infection, and their reduced ability to clear infections. Such studies imply that novel approaches unique to the neonate will be required for the development of both diagnostics and therapeutics in this high at-risk population.

Matrix Metalloproteinase-8 Augments Bacterial Clearance in a Juvenile Sepsis Model

Genetic ablation or pharmacologic inhibition of matrix metalloproteinase-8 (MMP8) improves survival in an adult murine sepsis model. Because developmental age influences the host inflammatory response, we hypothesized that developmental age influences the role of MMP8 in sepsis. First, we compared sepsis survival between wild type (WT, C57BL/6) and MMP8 null juvenile-aged mice (12-14 days) after intraperitoneal injection of a standardized cecal slurry. Second, peritoneal lavages collected at 6 and 18 hours after cecal slurry injection were analyzed for bacterial burden, leukocyte subsets, and inflammatory cytokines. Third, juvenile WT mice were pretreated with an MMP8 inhibitor prior to cecal slurry injection; analysis of their bacterial burden was compared to vehicle-injected animals. Fourth, the phagocytic capacity of WT and MMP8 null peritoneal macrophages was compared. Finally, peritoneal neutrophil extracellular traps (NETs) were compared using immunofluorescent imaging and quantitative image analysis. We found that juvenile MMP8 null mice had greater mortality and higher bacterial burden than WT mice. Leukocyte counts and cytokine concentrations in the peritoneal fluid were increased in the MMP8 null mice, relative to the wild type mice. Peritoneal macrophages from MMP8 null mice had reduced phagocytic capacity compared to WT macrophages. There was no quantitative difference in NET formation, but fewer bacteria were adherent to NETs from MMP8 null animals. In conclusion, in contrast to septic adult mice, genetic ablation of MMP8 increased mortality following bacterial peritonitis in juvenile mice. The increase in mortality in MMP8 null juvenile mice was associated with reduced bacterial clearance and reduced NET efficiency. We conclude that developmental age influences the role of MMP8 in sepsis.

Neonatal CD71+ Erythroid Cells Do Not Modify Murine Sepsis Mortality

Sepsis is a major cause of neonatal mortality and morbidity worldwide. A recent report suggested that murine neonatal host defense against infection could be compromised by immunosuppressive CD71(+) erythroid splenocytes. We examined the impact of CD71(+) erythroid splenocytes on murine neonatal mortality to endotoxin challenge or polymicrobial sepsis and characterized circulating CD71(+) erythroid (CD235a(+)) cells in human neonates. Adoptive transfer or an Ab-mediated reduction in neonatal CD71(+) erythroid splenocytes did not alter murine neonatal survival to endotoxin challenge or polymicrobial sepsis challenge. Ex vivo immunosuppression of stimulated adult CD11b(+) cells was not limited to neonatal splenocytes; it also occurred with adult and neonatal bone marrow. Animals treated with anti-CD71 Ab showed reduced splenic bacterial load following bacterial challenge compared with isotype-treated mice. However, adoptive transfer of enriched CD71(+) erythroid splenocytes to CD71(+)-reduced animals did not reduce bacterial clearance. Human CD71(+)CD235a(+) cells were common among cord blood mononuclear cells and were shown to be reticulocytes. In summary, a lack of effect on murine survival to polymicrobial sepsis following adoptive transfer or diminution of CD71(+) erythroid splenocytes under these experimental conditions suggests that the impact of these cells on neonatal infection risk and progression may be limited. An unanticipated immune priming effect of anti-CD71 Ab treatment, rather than a reduction in immunosuppressive CD71(+) erythroid splenocytes, was likely responsible for the reported enhanced bacterial clearance. In humans, the well-described rapid decrease in circulating reticulocytes after birth suggests that they may have a limited role in reducing inflammation secondary to microbial colonization.

Postnatal Age Is a Critical Determinant of the Neonatal Host Response to Sepsis

Neonates manifest a unique host response to sepsis even among other children. Preterm neonates may experience sepsis soon after birth or during often-protracted birth hospitalizations as they attain physiologic maturity. We examined the transcriptome using genome-wide expression profiling on prospectively collected peripheral blood samples from infants evaluated for sepsis within 24 h after clinical presentation. Simultaneous plasma samples were examined for alterations in inflammatory mediators. Group designation (sepsis or uninfected) was determined retrospectively on the basis of clinical exam and laboratory results over the next 72 h from the time of evaluation. Unsupervised analysis showed the major node of separation between groups was timing of sepsis episode relative to birth (early, <3 d, or late, ≥3 d). Principal component analyses revealed significant differences between patients with early or late sepsis despite the presence of similar key immunologic pathway aberrations in both groups. Unique to neonates, the uninfected state and host response to sepsis is significantly affected by timing relative to birth. Future therapeutic approaches may need to be tailored to the timing of the infectious event based on postnatal age.

Infections and risk-adjusted length of stay and hospital mortality in Polish Neonatology Intensive Care Units

BACKGROUND

The objectives of this study were to analyze the impact of infections on prolonging hospital stay with consideration of underlying risk factors and determining the mortality rates and its association with infections.

METHODS

An electronic database developed from a continuous prospective targeted infection surveillance program was used in the study. Data were collected from 2009 to 2012 in five Polish tertiary academic neonatal intensive care units (NICUs). The length of stay (LOS) of 2,003 very low birth weight (VLBW) neonates was calculated as the sum of the number of days since birth until death or until reaching a weight of 1,800g.

RESULTS

The median LOS for neonates with infections was twice as high as for neonates without infection. LOS was significantly affected by the overall general condition of the neonate, as expressed by both gestational age and birth weight as well as by the Clinical Risk Index for Babies (CRIB) score; another independent factor was presence of at least one infection. Risk of in-hospital mortality was significantly increased by male sex and vaginal birth and was lower among breastfed neonates. Deaths were significantly more frequent in neonates without infection.

CONCLUSIONS

The general condition of VLBW infants statistically increase both their risk of mortality and LOS; this is in contrast to the presence of infection, which significantly prolonged LOS only.

miR-15a/16 are upreuglated in the serum of neonatal sepsis patients and inhibit the LPS-induced inflammatory pathway

Infection in neonates, particular the neonatal sepsis continues to be a global problem with significant morbidity and mortality. The diagnosis of neonatal sepsis is complicated by nonspecific clinical symptomatology, a high-false negative rate, and a delay in obtaining blood culture results. MicroRNAs (miRNAs) have recently been used as finger prints for sepsis, and have been validated to be potential sepsis biomarker recently. In the present study, we investigated the level of several miRNAs, such as miR-15a, miR-16, miR-15b, and miR-223, which have been identified as a biomarker in adult sepsis, in neonatal sepsis patients, and then we analyzed the association of miR-15a/16 with the patient prognosis. Results demonstrated that the level of miR-15a/16 was up-regulated in neonatal sepsis patients than in normal neonatal subjects; however, no statistical difference was disclosed in the miR-15b and miR-223 level between two groups. And the ROC analysis indicated the miR-15a and miR-16 were potent fingerprints for diagnosing neonate sepsis. In order to explore the miR-15a/16 function on the lipopolysaccharide (LPS)-induced inflammatory pathway, the mice macrophage RAW264.7 cells were transiently transfected with miR-15a/16 mimics. And it was demonstrated that the miR-15a/16 transfection down-regulated the Toll-like receptor 4 (TLR4) and Interleukin-1 receptor-associated kinase 1 (IRAK-1) transcription level with a statistical difference in the LPS treated cells. And the suppression capability of miR-15a/16 on the expression of TLR-4 and IRAK-1 were evaluated by western blot. Thus, in present study, we identified miR-15a/16 as potential biomarker for the diagnosis and prognosis of neonatal sepsis, and the upregulated miR-15a/16 downregulated the LPS-induced inflammatory pathway.

Different expressions of TLRs and related factors in peripheral blood of preterm infants

OBJECTIVE

TLR insufficiency increases newborn's susceptibility to infectious disease.

METHODS

The peripheral blood of four premature births has been collected weekly from the 28(th) gestational week (GW) until maturity at 36(th) GW. Microarray assays were used to derive dynamic follow-up data of TLR1-10 and other TLR signaling pathway associated factor changes.

RESULTS

The follow-up results showed that the transcription level of TLR1 increased at the 36(th), TLR 3 decreased at the 33(rd) and TLR7 increased at the 34(th) GW significantly, whereas NFkB and its activator TBK1 were highest transcribed in the 28(th) and 32(nd) GW. Low TLR4 transcription in addition to late MD-2 maturation (33(rd) GW) indicated a lack of defense mechanisms against bacterial infections in preterm births particular in the first weeks after birth. Late transcriptional enhancements of TLR1 and MYD88 (35(th) week) as well as β 2 microglobulin (35(th) GW) also indicated a weak immune system in the early maturation stages.

CONCLUSION

The transcription levels of TLR1, 3, 7 and the signaling pathway associated cofactors were different transcribed during the 28(th) and 36(th) GWs of the premature newborns. In the early stage after preterm birth, beside peak transcriptions of NFkB and TBK1, the immune system is not fully developed and maturation takes place mainly between the 33th and 35(th) GW.

Time for a neonatal-specific consensus definition for sepsis

OBJECTIVE

To review the accuracy of the pediatric consensus definition of sepsis in term neonates and to determine the definition of neonatal sepsis used.

STUDY SELECTION

The review focused primarily on pediatric literature relevant to the topic of interest.

CONCLUSIONS

Neonatal sepsis is variably defined based on a number of clinical and laboratory criteria that make the study of this common and devastating condition very difficult. Diagnostic challenges and uncertain disease epidemiology necessarily result from a variable definition of disease. In 2005, intensivists caring for children recognized that as new drugs became available, children would be increasingly studied and thus, pediatric-specific consensus definitions were needed. Pediatric sepsis criteria are not accurate for term neonates and have not been examined in preterm neonates for whom the developmental stage influences aberrations associated with host immune response. Thus, specific consensus definitions for both term and preterm neonates are needed. Such definitions are critical for the interpretation of observational studies, future training of scientists and practitioners, and implementation of clinical trials in neonates.

The pediatric sepsis biomarker risk model: potential implications for sepsis therapy and biology

Sepsis remains a major cause of morbidity and mortality in adult and pediatric intensive care units. Heterogeneity of demographics, comorbidities, biological mechanisms, and severity of illness leads to difficulty in determining which patients are at highest risk of mortality. Determining mortality risk is important for weighing the potential benefits of more aggressive interventions and for deciding whom to enroll in clinical trials. Biomarkers can be used to parse patients into different risk categories and can outperform current methods of patient risk stratification based on physiologic parameters. Here we review the Pediatric Sepsis Biomarker Risk Model that has also been modified and applied to estimate mortality risk in adult patients. We compare the two models and speculate on the biological implications of the biomarkers in patients with sepsis.

Altered miRNAs expression profiles and modulation of immune response genes and proteins during neonatal sepsis

PURPOSE

The dysregulated expression of miRNAs in the immune system may be critical for immune responses to pathogens and evolve into the inflammation seen in sepsis. The aim of this study is to explore the important role of miRNAs in the regulation of the immune response during neonatal sepsis.

METHODS

Using a microarray we performed the miRNA expression profiling of peripheral blood leukocytes from neonates with sepsis and uninfected neonates. Based on the predicted target genes of these miRNAs we selected 26 immune-related miRNAs out of the differentially expressed miRNAs for further testing by quantitative PCR. We simultaneously detected the immune response genes by PCR array and plasma cytokine levels using a protein chip to investigate the effect of the altered miRNAs on the immune response in neonatal sepsis.

RESULTS

There were 10 immune regulatory miRNAs whose expression was significantly changed more than two fold in the neonates with sepsis compared with the uninfected neonates. The expression levels of 11 immune response genes and the plasma levels of 15 cytokines or receptors were significantly up- or down-regulated in the neonates with sepsis compared to the uninfected neonates. This comprehensive analysis suggests that the altered miRNAs modulate the immune response during neonatal sepsis in a way that represses the inflammatory response.

CONCLUSIONS

Our investigation demonstrated some miRNAs with altered expression levels and their probable association with the regulation of immune response during neonatal sepsis. The characteristics of the neonatal inflammatory response could be attributed to immature immune function of neonates.

A prime time for trained immunity: innate immune memory in newborns and infants

The newborn and infant periods of early life are associated with heightened vulnerability to infection. Limited antigen exposure and distinct adaptive immune function compared to the adult places a greater burden on innate immunity for host defense to microbial challenge during this time. Trained immunity describes the phenomenon of augmented innate immune function following a stimulus that is not specific to the original stimulus. We review the concept of trained immunity in the context of the newborn's unique innate immune system function, the preclinical and clinical evidence that supports the tenet of innate immune memory in early life, and potential consequences of altered innate immune host responses.

Sepsis: multiple abnormalities, heterogeneous responses, and evolving understanding

Sepsis represents the host's systemic inflammatory response to a severe infection. It causes substantial human morbidity resulting in hundreds of thousands of deaths each year. Despite decades of intense research, the basic mechanisms still remain elusive. In either experimental animal models of sepsis or human patients, there are substantial physiological changes, many of which may result in subsequent organ injury. Variations in age, gender, and medical comorbidities including diabetes and renal failure create additional complexity that influence the outcomes in septic patients. Specific system-based alterations, such as the coagulopathy observed in sepsis, offer both potential insight and possible therapeutic targets. Intracellular stress induces changes in the endoplasmic reticulum yielding misfolded proteins that contribute to the underlying pathophysiological changes. With these multiple changes it is difficult to precisely classify an individual's response in sepsis as proinflammatory or immunosuppressed. This heterogeneity also may explain why most therapeutic interventions have not improved survival. Given the complexity of sepsis, biomarkers and mathematical models offer potential guidance once they have been carefully validated. This review discusses each of these important factors to provide a framework for understanding the complex and current challenges of managing the septic patient. Clinical trial failures and the therapeutic interventions that have proven successful are also discussed.

Neonatal sepsis due to coagulase-negative staphylococci

Neonates, especially those born prematurely, are at high risk of morbidity and mortality from sepsis. Multiple factors, including prematurity, invasive life-saving medical interventions, and immaturity of the innate immune system, put these infants at greater risk of developing infection. Although advanced neonatal care enables us to save even the most preterm neonates, the very interventions sustaining those who are hospitalized concurrently expose them to serious infections due to common nosocomial pathogens, particularly coagulase-negative staphylococci bacteria (CoNS). Moreover, the health burden from infection in these infants remains unacceptably high despite continuing efforts. In this paper, we review the epidemiology, immunological risk factors, diagnosis, prevention, treatment, and outcomes of neonatal infection due to the predominant neonatal pathogen CoNS.

The immune consequences of preterm birth

Preterm birth occurs in 11% of live births globally and accounts for 35% of all newborn deaths. Preterm newborns have immature immune systems, with reduced innate and adaptive immunity; their immune systems may be further compromised by various factors associated with preterm birth. The immune systems of preterm infants have a smaller pool of monocytes and neutrophils, impaired ability of these cells to kill pathogens, and lower production of cytokines which limits T cell activation and reduces the ability to fight bacteria and detect viruses in cells, compared to term infants. Intrauterine inflammation is a major contributor to preterm birth, and causes premature immune activation and cytokine production. This can induce immune tolerance leading to reduced newborn immune function. Intrauterine inflammation is associated with an increased risk of early-onset sepsis and likely has long-term adverse immune consequences. Requisite medical interventions further impact on immune development and function. Antenatal corticosteroid treatment to prevent newborn respiratory disease is routine but may be immunosuppressive, and has been associated with febrile responses, reductions in lymphocyte proliferation and cytokine production, and increased risk of infection. Invasive medical procedures result in an increased risk of late-onset sepsis. Respiratory support can cause chronic inflammatory lung disease associated with increased risk of long-term morbidity. Colonization of the infant by microorganisms at birth is a significant contributor to the establishment of the microbiome. Caesarean section affects infant colonization, potentially contributing to lifelong immune function and well-being. Several factors associated with preterm birth alter immune function. A better understanding of perinatal modification of the preterm immune system will allow for the refinement of care to minimize lifelong adverse immune consequences.

Neonatal immune adaptation of the gut and its role during infections

The intestinal tract is engaged in a relationship with a dense and complex microbial ecosystem, the microbiota. The establishment of this symbiosis is essential for host physiology, metabolism, and immune homeostasis. Because newborns are essentially sterile, the first exposure to microorganisms and environmental endotoxins during the neonatal period is followed by a crucial sequence of active events leading to immune tolerance and homeostasis. Contact with potent immunostimulatory molecules starts immediately at birth, and the discrimination between commensal bacteria and invading pathogens is essential to avoid an inappropriate immune stimulation and/or host infection. The dysregulation of these tight interactions between host and microbiota can be responsible for important health disorders, including inflammation and sepsis. This review summarizes the molecular events leading to the establishment of postnatal immune tolerance and how pathogens can avoid host immunity and induce neonatal infections and sepsis.

Early sepsis does not increase the risk of late sepsis in very low birth weight neonates

OBJECTIVE

To examine whether preterm very low birth weight (VLBW) infants have an increased risk of late-onset sepsis (LOS) following early-onset sepsis (EOS).

STUDY DESIGN

Retrospective analysis of VLBW infants (401-1500 g) born September 1998 through December 2009 who survived >72 hours and were cared for within the National Institute of Child Health and Human Development Neonatal Research Network. Sepsis was defined by growth of bacteria or fungi in a blood culture obtained ≤ 72 hours of birth (EOS) or >72 hours (LOS) and antimicrobial therapy for ≥ 5 days or death <5 days while receiving therapy. Regression models were used to assess risk of death or LOS by 120 days and LOS by 120 days among survivors to discharge or 120 days, adjusting for gestational age and other covariates.

RESULTS

Of 34,396 infants studied, 504 (1.5%) had EOS. After adjustment, risk of death or LOS by 120 days did not differ overall for infants with EOS compared with those without EOS [risk ratio (RR): 0.99 (0.89-1.09)] but was reduced in infants born at <25 weeks gestation [RR: 0.87 (0.76-0.99), P = .048]. Among survivors, no difference in LOS risk was found overall for infants with versus without EOS [RR: 0.88 (0.75-1.02)], but LOS risk was reduced in infants with birth weight 401-750 g who had EOS [RR: 0.80 (0.64-0.99), P = .047].

CONCLUSIONS

Risk of LOS after EOS was not increased in VLBW infants. Surprisingly, risk of LOS following EOS appeared to be reduced in the smallest, most premature infants, underscoring the need for age-specific analyses of immune function.

Inefficient antimicrobial functions of innate phagocytes render infant mice more susceptible to bacterial infection

Neonates and infants, due to the immaturity in their adaptive immunity, are thought to depend largely on the innate immune system for protection against bacterial infection. However, the innate immunity-mediated antimicrobial response in neonates and infants is incompletely characterized. Here, we report that infant mice were more susceptible to microbial sepsis than adult mice, with significantly reduced bacterial clearance from the circulation and visceral organs. Infant PMNs exhibited less constitutive expression of the chemokine receptor CXCR2, and bacterial infection caused further reduction of PMN CXCR2 in infant mice compared with adult mice. This correlates with diminished in vitro chemotaxis of infant PMNs toward the chemoattractant CXCL2 and impaired in vivo recruitment of infant PMNs into the infectious site. Furthermore, consistent with the reduced antimicrobial response in vivo, infant macrophages displayed an impaired bactericidal activity with a defect in phagosome maturation after ingestion of either gram-positive or gram-negative bacteria. Thus, infant mice exhibit an increased vulnerability to microbial infection with delayed bacterial clearance, which is associated with the inefficiency in their innate phagocyte-associated antimicrobial functions characterized by defects in PMN recruitment and macrophage phagosome maturation during microbial sepsis.

Very low birth weight neonates who survive early-onset sepsis do not have an increased risk of developing late-onset sepsis

BACKGROUND

Very low birth weight neonates (≤ 1500 g, VLBWs) have a high rate of infection and distinct baseline immune function compared with more mature populations. In critically ill children and adults, sepsis increases subsequent infection risk. It is unknown whether sepsis modifies the risk of subsequent infection in VLBWs.

METHODS

We conducted a retrospective cohort study of VLBWs≤32weeks of gestation at birth cared for in 312 neonatal intensive care units in the United States from 1997 to 2011 (n=103,376). Early-onset sepsis (EOS, culture-positive only) and late-onset sepsis (LOS, culture-positive or clinical) cases were identified. Cox proportional hazard models were used to control for clinical variables between neonates with and without EOS to determine if EOS modified risk of LOS, necrotizing enterocolitis (NEC), or death.

RESULTS

LOS occurred in 12,112/102,317 (11.8%) neonates without EOS and in 133/1059 (12.6%) of those with EOS. After adjustment for clinical variables, the risk of LOS was not different between neonates with or without a history of EOS (hazard ratio [HR]=0.92; 95% confidence interval [CI] 0.74, 1.16). EOS increased the risk of 120-day mortality (HR=1.78; 95% CI 1.49, 2.13).

CONCLUSIONS

In contrast to findings in children and adults, EOS was not associated with an increased risk of LOS in this cohort. Age-specific investigations are needed to determine if post-sepsis immunologic alterations are present.

The neonatal immune system: immunomodulation of infections in early life

The innate and adaptive immune responses in neonates are usually functionally impaired when compared with their adult counterparts. The qualitative and quantitative differences in the neonatal immune response put them at risk for the development of bacterial and viral infections, resulting in increased mortality. Newborns often exhibit decreased production of Th1-polarizing cytokines and are biased toward Th2-type responses. Studies aimed at understanding the plasticity of the immune response in the neonatal and early infant periods or that seek to improve neonatal innate immune function with adjuvants or special formulations are crucial for preventing the infectious disease burden in this susceptible group. Considerable studies focused on identifying potential immunomodulatory therapies have been performed in murine models. This article highlights the strategies used in the emerging field of immunomodulation in bacterial and viral pathogens, focusing on preclinical studies carried out in animal models with particular emphasis on neonatal-specific immune deficits.

Changes in fetal thymic immune cell populations in a sheep model of intrauterine inflammation

Intrauterine inflammation is a common antecedent of preterm birth and can alter the development of the fetal thymus, the site of development, and maturation of T lymphocytes. The effects of intrauterine inflammation on specific thymic T lymphocyte populations are largely unknown. We hypothesized that intrauterine inflammation would alter fetal thymic T cell populations. Immunohistochemistry was used to quantitate the relative proportions of thymic cortical and medullary cell populations in fetal sheep 7 days after intra-amniotic lipopolysaccharide (LPS) injection. The proportions of CD8⁺and MHC II⁺ cells in the fetal thymus were reduced in response to LPS. The ratio of CD4:CD8 cells was increased by LPS exposure. No changes were observed in the percentage of CD4⁺, γδ(WC1)⁺, CD45R⁺B cells, or CD44⁺ cells. These studies indicate that intrauterine inflammation impacts thymic composition of CD8 T cells and the development and/or activation of CD4 T cells in the fetal thymus.

Pediatric Sepsis - Part I: "Children are not small adults!"

The recognition, diagnosis, and management of sepsis remain among the greatest challenges in pediatric critical care medicine. Sepsis remains among the leading causes of death in both developed and underdeveloped countries and has an incidence that is predicted to increase each year. Unfortunately, promising therapies derived from preclinical models have universally failed to significantly reduce the substantial mortality and morbidity associated with sepsis. There are several key developmental differences in the host response to infection and therapy that clearly delineate pediatric sepsis as a separate, albeit related, entity from adult sepsis. Thus, there remains a critical need for well-designed epidemiologic and mechanistic studies of pediatric sepsis in order to gain a better understanding of these unique developmental differences so that we may provide the appropriate treatment. Herein, we will review the important differences in the pediatric host response to sepsis, highlighting key differences at the whole-organism level, organ system level, and cellular and molecular level.

Randomized trial of BCG vaccination at birth to low-birth-weight children: beneficial nonspecific effects in the neonatal period?

BACKGROUND

Observational studies have suggested that BCG may have nonspecific beneficial effects on survival. Low-birth-weight (LBW) children are not given BCG at birth in Guinea-Bissau; we conducted a randomized trial of BCG at birth (early BCG) vs delayed BCG.

METHODS

In the period 2004-2008 we recruited 2320 LBW children in Bissau. The children were visited at home at 2, 6, and 12 months of age. With a pretrial infant mortality of 250 per 1000, we hypothesized a 25% reduction in infant mortality for LBW children.

RESULTS

Infant mortality was only 101 per 1000 during the trial. In the primary analysis, infant mortality was reduced insignificantly by 17% (mortality rate ratio [MRR] = .83 [.63-1.08]). In secondary analyses, early BCG vaccine was safe with an MRR of .49 (.21-1.15) after 3 days and .55 (.34-.89) after 4 weeks. The reduction in neonatal mortality was mainly due to fewer cases of neonatal sepsis, respiratory infection, and fever. The impact of early BCG on infant mortality was marked for children weighing <1.5 kg (MRR = .43 [.21-.85]) who had lower coverage for diphtheria-tetanus-pertussis vaccinations.

CONCLUSIONS

Though early BCG did not reduce infant mortality significantly, it may have a beneficial effect in the neonatal period. This could be important for public health because BCG is often delayed in low-income countries.

The influence of developmental age on the early transcriptomic response of children with septic shock

Septic shock is a frequent and costly problem among patients in the pediatric intensive care unit (PICU) and is associated with high mortality and devastating survivor morbidity. Genome-wide expression patterns can provide molecular granularity of the host response and offer insight into why large variations in outcomes exist. We derived whole-blood genome-wide expression patterns within 24 h of PICU admission from children with septic shock. We compared the transcriptome between septic shock developmental-age groups defined as neonates (≤ 28 d, n = 17), infants (1 month to 1 year, n = 62), toddlers (2-5 years, n = 54) and school-age (≥ 6 years, n = 47) and age-matched controls. Direct intergroup comparisons demonstrated profound changes in neonates, relative to older children. Neonates with septic shock demonstrated reduced expression of genes representing key pathways of innate and adaptive immunity. In contrast to the largely upregulated transcriptome in all other groups, neonates exhibited a predominantly downregulated transcriptome when compared with controls. Neonates and school-age subjects had the most uniquely regulated genes relative to controls. Age-specific studies of the host response are necessary to identify developmentally relevant translational opportunities that may lead to improved sepsis outcomes.