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

Metabolic trade-offs in Neonatal sepsis triggered by TLR4 and TLR1/2 ligands result in unique dysfunctions in neural breathing circuits

Neonatal sepsis remains one of the leading causes of mortality in newborns. Several brainstem-regulated physiological processes undergo disruption during neonatal sepsis. Mechanistic knowledge gaps exist at the interplay between metabolism and immune activation to brainstem neural circuits and pertinent physiological functions in neonates. To delineate this association, we induced systemic inflammation either by TLR4 (LPS) or TLR1/2 (PAM3CSK4) ligand administration in postnatal day 5 mice (PD5). Our findings show that LPS and PAM3CSK4 evoke substantial changes in respiration and metabolism. Physiological trade-offs led to hypometabolic-hypothermic responses due to LPS, but not PAM3CSK4, whereas to both TLR ligands blunted respiratory chemoreflexes. Neuroinflammatory pathways modulation in brainstem showed more robust effects in LPS than PAM3CSK4. Brainstem neurons, microglia, and astrocyte gene expression analyses showed unique responses to TLR ligands. PAM3CSK4 did not significantly modulate gene expression changes in GLAST-1 positive brainstem astrocytes. PD5 pups receiving PAM3CSK4 failed to maintain a prolonged metabolic state repression, which correlated to enhanced gasping latency and impaired autoresuscitation during anoxic chemoreflex challenges. In contrast, LPS administered pups showed no significant changes in anoxic chemoreflex. Electrophysiological studies from brainstem slices prepared from pups exposed to either TLR4 or PAM3CSK4 showed compromised transmission between preBötzinger complex and Hypoglossal as an exclusive response to the TLR1/2 ligand. Spatial gene expression analysis demonstrated a region-specific modulation of PAM3CSK4 within the raphe nucleus relative to other anatomical sites evaluated. Our findings suggest that metabolic changes due to inflammation might be a crucial tolerance mechanism for neonatal sepsis preserving neural control of breathing.

Neonatal bacterial sepsis

Neonatal sepsis remains one of the key challenges of neonatal medicine, and together with preterm birth, causes almost 50% of all deaths globally for children younger than 5 years. Compared with advances achieved for other serious neonatal and early childhood conditions globally, progress in reducing neonatal sepsis has been much slower, especially in low-resource settings that have the highest burden of neonatal sepsis morbidity and mortality. By contrast to sepsis in older patients, there is no universally accepted neonatal sepsis definition. This poses substantial challenges in clinical practice, research, and health-care management, and has direct practical implications, such as diagnostic inconsistency, heterogeneous data collection and surveillance, and inappropriate treatment, health-resource allocation, and education. As the clinical manifestation of neonatal sepsis is frequently non-specific and the current diagnostic standard blood culture has performance limitations, new improved diagnostic techniques are required to guide appropriate and warranted antimicrobial treatment. Although antimicrobial therapy and supportive care continue as principal components of neonatal sepsis therapy, refining basic neonatal care to prevent sepsis through education and quality improvement initiatives remains paramount.

Life-threatening infections in human newborns: Reconciling age-specific vulnerability and interindividual variability

In humans, the interindividual variability of clinical outcome following exposure to a microorganism is immense, ranging from silent infection to life-threatening disease. Age-specific immune responses partially account for the high incidence of infection during the first 28 days of life and the related high mortality at population level. However, the occurrence of life-threatening disease in individual newborns remains unexplained. By contrast, inborn errors of immunity and their immune phenocopies are increasingly being discovered in children and adults with life-threatening viral, bacterial, mycobacterial and fungal infections. There is a need for convergence between the fields of neonatal immunology, with its in-depth population-wide characterization of newborn-specific immune responses, and clinical immunology, with its investigations of infections in patients at the cellular and molecular levels, to facilitate identification of the mechanisms of susceptibility to infection in individual newborns and the design of novel preventive and therapeutic strategies.

Intravenous lipopolysaccharide challenge in early versus mid-lactation dairy cattle. I: The immune and inflammatory responses

Cows in early lactation (EL) are purportedly immune suppressed, which renders them more susceptible to disease. Thus, the study objective was to compare key biomarkers of immune activation from i.v. lipopolysaccharide (LPS) between EL and mid-lactation (ML) cows. Multiparous EL (20 ± 2 DIM; n = 11) and ML (131 ± 31 DIM; n = 12) cows were enrolled in a 2 × 2 factorial design and assigned to 1 of 2 treatments by lactation stage (LS): (1) EL (EL-LPS; n = 6) or ML (ML-LPS; n = 6) cows administered a single LPS bolus from Escherichia coli O55:B5 (0.09 µg/kg of body weight), or (2) pair-fed (PF) EL (EL-PF; n = 5) or ML (ML-PF; n = 6) cows administered i.v. saline. After LPS administration, cows were intensely evaluated for 3 d to analyze their response and recovery to LPS. Rectal temperature increased in LPS relative to PF cows (1.1°C in the first 9 h), and the response was more severe in EL-LPS relative to ML-LPS cows (2.3 vs. 1.3°C increase at 4 h post-LPS; respectively). Respiration rate increased only in EL-LPS cows (47% relative to ML-LPS in the first h post-LPS). Circulating tumor necrosis factor-α, IL-6, monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-1α, MIP-1β, and IFN-γ-inducible protein-10 increased within the first 6 h after LPS and these changes were exacerbated in EL-LPS relative to ML-LPS cows (6.3-, 4.8-fold, 57%, 93%, 10%, and 61% respectively). All cows administered LPS had decreased circulating iCa relative to PF cows (34% at the 6 h nadir), but the hypocalcemia was more severe in EL-LPS than ML-LPS cows (14% at 6 h nadir). In response to LPS, neutrophils decreased regardless of LS, then increased into neutrophilia by 24 h in all LPS relative to PF cows (2-fold); however, the neutrophilic phase was augmented in EL- compared with ML-LPS cows (63% from 24 to 72 h). Lymphocytes and monocytes rapidly decreased then gradually returned to baseline in LPS cows regardless of LS; however, monocytes were increased (57%) at 72 h in EL-LPS relative to ML-LPS cows. Platelets were reduced (46%) in LPS relative to PF cows throughout the 3-d following LPS, and from 24 to 48 h, platelets were further decreased (41%) in EL-LPS compared with ML-LPS. During the 3-d following LPS, serum amyloid A (SAA), LPS-binding protein (LBP), and haptoglobin (Hp) increased in LPS compared with PF groups (9-fold, 72%, and 153-fold, respectively), and the LBP and Hp responses were more exaggerated in EL-LPS than ML-LPS cows (85 and 79%, respectively) whereas the SAA response did not differ by LS. Thus, our data indicates that EL immune function does not appear "suppressed," and in fact many aspects of the immune response are seemingly functionally robust.

Antibacterial, antidiabetic, acute toxicity, antioxidant, and nephroproductive competence of extracts of Lannea coromandelica fruit through in-vitro and in-vivo animal model investigation

The anti-dermatophytic (Proteus vulgaris, Klebsiella pneumoniae, Enterobacter aerogenes, Propionibacterium acnes, Staphylococcus aureus, and Streptococcus pyogenes) and nephroprotective activities of methanol and aqueous extracts obtained from Lannea coromandelica fruit were investigated through in-vitro (agar well diffusion method) and in-vivo (animal model) study. The methanol extract showed considerable antibacterial activity against selective bacterial pathogens at increased concentration (15.0 mg mL-1) in the following order P. vulgaris (35.2 ± 1.6 mm) > E. aerogenes (32.1 ± 2.1 mm) > K. pneumoniae (29.3±2 mm) > P. acnes (28.2 ± 2.4 mm) > S. aureus (25.5 ± 2.4 mm) > S. pyogenes (24.3 ± 2.1 mm) than aqueous extract. The MIC values of this methanol and aqueous extract was found as 2.5-7.5 mg mL-1 and 5.0 to 1.0 mg mL-1 respectively. Different treatment sets (A-E) on a rat-based animal model study revealed that the methanol extract has excellent antioxidant and nephroprotective activity, as well as favorable effects on essential biochemical substances involved in active metabolic activities. As demonstrated by histopathological and microscopic examination, the biologically active chemical present in methanol extract had a positive effect on serum markers, enzyme, and non-enzyme-based antioxidant activities, as well as lowering the toxicity caused by EG in the rat (as nephroprotective activity) renal cells.

Ultra-High Temperature Treatment of Liquid Infant Formula, Systemic Immunity, and Kidney Development in Preterm Neonates

SCOPE

Ready-to-feed liquid infant formulas (IFs) are increasingly being used for newborn preterm infants when human milk is unavailable. However, sterilization of liquid IFs by ultra-high temperature (UHT) introduces Maillard reaction products (MRPs) that may negatively affect systemic immune and kidney development.

METHODS AND RESULTS

UHT-treated IF without and with prolonged storage (SUHT) are tested against pasteurized IF (PAST) in newborn preterm pigs as a model for preterm infants. After 5 days, blood leukocytes, markers of systemic immunity and inflammation, kidney structure and function are evaluated. No consistent differences between UHT and PAST pigs are observed. However, SUHT increases plasma TNFα and IL-6 and reduces neutrophils and in vitro response to LPS. In SUHT pigs, the immature kidneys show minor upregulation of gene expressions related to inflammation (RAGE, MPO, MMP9) and oxidative stress (CAT, GLO1), together with glomerular mesangial expansion and cell injury. The increased inflammatory status in SUHT pigs appears unrelated to systemic levels of MRPs.

CONCLUSION

SUHT feeding may impair systemic immunity and affect kidney development in preterm newborns. The systemic effects may be induced by local gut inflammatory effects of MRPs. Optimal processing and length of storage are critical for UHT-treated liquid IFs for preterm infants.

New Insights in Immunometabolism in Neonatal Monocytes and Macrophages in Health and Disease

It is well established that the neonatal immune system is different from the adult immune system. A major task of the neonatal immune system is to bridge the achievement of tolerance towards harmless antigens and commensal bacteria while providing protection against pathogens. This is highly important because neonates are immunologically challenged directly after birth by a rigorous change from a semi-allogeneic sterile environment into a world rich with microbes. A so called disease tolerogenic state is typical for neonates and is anticipated to prevent immunopathological damage potentially at the cost of uncontrolled pathogen proliferation. As a consequence, neonates are more susceptible than adults to life-threatening infections. At the basis of a well-functioning immune response, both for adults and neonates, innate immune cells such as monocytes and monocyte-derived macrophages play an essential role. A well-responsive monocyte will alter its cellular metabolism to subsequently induce certain immune effector function, a process which is called immunometabolism. Immunometabolism has received extensive attention in the last decade; however, it has not been broadly studied in neonates. This review focuses on carbohydrate metabolism in monocytes and macrophages in neonates. We will exhibit pathways involving glycolysis, the tricarboxylic acid (TCA) cycle and oxidative phosphorylation and their role in shaping neonates' immune systems to a favorable tolerogenic state. More insight into these pathways will elucidate potential treatments targets in life-threatening conditions including neonatal sepsis or expose potential targets which can be used to induce tolerance in conditions where tolerance is harmfully impaired such as in autoimmune diseases.

BCG-Induced Immune Training: Interplay between Trained Immunity and Emergency Granulopoiesis

Bacille Calmette-Guérin (BCG) is the most commonly administered vaccine in human history. The medical application of BCG extends far beyond the fight against tuberculosis. Despite its stellar medical record over 100 years, insight into how BCG provides this vast range of benefits is largely limited, both for its pathogen-specific (tuberculosis) as well as pathogen-agnostic (other infections, autoimmunity, allergies, and cancer) effects. Trained immunity and emergency granulopoiesis have been identified as mediating BCG's pathogen-agnostic effects, for which some of the molecular mechanisms have been delineated. Upon review of the existing evidence, we postulate that emergency granulopoiesis and trained immunity are a continuum of the same effect cascade. In this context, we highlight that BCG's pathogen-agnostic benefits could be optimized by taking advantage of the age of the recipient and route of BCG administration.

Maternal vaccination to prevent adverse pregnancy outcomes: An underutilized molecular immunological intervention?

Adverse pregnancy outcomes including maternal mortality, stillbirth, preterm birth, intrauterine growth restriction cause millions of deaths each year. More effective interventions are urgently needed. Maternal immunization could be one such intervention protecting the mother and newborn from infection through its pathogen-specific effects. However, many adverse pregnancy outcomes are not directly linked to the infectious pathogens targeted by existing maternal vaccines but rather are linked to pathological inflammation unfolding during pregnancy. The underlying pathogenesis driving such unfavourable outcomes have only partially been elucidated but appear to relate to altered immune regulation by innate as well as adaptive immune responses, ultimately leading to aberrant maternal immune activation. Maternal immunization, like all immunization, impacts the immune system beyond pathogen-specific immunity. This raises the possibility that maternal vaccination could potentially be utilised as a pathogen-agnostic immune modulatory intervention to redirect abnormal immune trajectories towards a more favourable phenotype providing pregnancy protection. In this review we describe the epidemiological evidence surrounding this hypothesis, along with the mechanistic plausibility and present a possible path forward to accelerate addressing the urgent need of adverse pregnancy outcomes.

Programmed and environmental determinants driving neonatal mucosal immune development

The mucosal immune system of neonates goes through successive, non-redundant phases that support the developmental needs of the infant and ultimately establish immune homeostasis. These phases are informed by environmental cues, including dietary and microbial stimuli, but also evolutionary developmental programming that functions independently of external stimuli. The immune response to exogenous stimuli is tightly regulated during early life; thresholds are set within this neonatal "window of opportunity" that govern how the immune system will respond to diet, the microbiota, and pathogenic microorganisms in the future. Thus, changes in early-life exposure, such as breastfeeding or environmental and microbial stimuli, influence immunological and metabolic homeostasis and the risk of developing diseases such as asthma/allergy and obesity.

Biomaterial mediated simultaneous delivery of spermine and alpha ketoglutarate modulate metabolism and innate immune cell phenotype in sepsis mouse models

Although different metabolic pathways have been associated with distinct macrophage phenotypes, the field of utilizing metabolites to modulate macrophage phenotype is in a nascent stage. In this report, we developed microparticles based on polymerization of alpha-ketoglutarate (a Krebs cycle metabolite), with or without encapsulation of spermine (a polyamine metabolite), to modulate cell phenotype that are critical for resolution of inflammation. Poly (alpha-ketoglutarate) microparticles encapsulated and released spermine (spermine (encap)paKG MPs) in vitro, which was accelerated in an acidic environment. When delivered to bone marrow-derived-macrophages, spermine (encap)paKG MPs induced a complex phenotypic profile outside of the typical M1/M2 paradigm, with distinct effects in the presence or absence of the pro-inflammatory stimulus lipopolysaccharide. Of particular interest was the increase in expression of CD163, which has been linked to anti-inflammatory responses in sepsis. Therefore, we systemically administered spermine (encap)paKG MPs to two different murine models of sepsis using acute or chronic injection of LPS. Macrophages and neutrophils in the liver and spleen of animals treated with spermine (encap)paKG MPs increased expression of CD163, concomitant with normalizing of glycolysis and oxidative phosphorylation, in both models. Overall, these results show that spermine (encap)paKG MPs modulate macrophage phenotype in vitro and in vivo, with potential applications in inflammation-associated diseases.

Challenging molecular dogmas in human sepsis using mathematical reasoning

Sepsis is defined as a dysregulated host-response to infection, across all ages and pathogens. What defines a dysregulated state remains intensively researched but incompletely understood. Here, we dissect the meaning of this definition and its importance for the diagnosis and management of sepsis. We deliberate on pathophysiological features and dogmas that range from cytokine storms and immune paralysis to dormancy and altered homeostasis setpoints. Mathematical reasoning, used to test for plausibility, reveals three interlinked cardinal rules governing host-response trajectories in sepsis. Rule one highlights that the amplitude of the immune response while important is not sufficient and is strictly dependent on rule two, specifying bioenergetic capacity and are together dynamically driven by rule three, delineating stability and alterations in setpoints. We consider these rules and associated pathophysiological parameters for guiding data-science and artificial intelligence mining of multi-omics and big-data for improving the precision of diagnostic and therapeutic approaches to sepsis.

Funding

PG funded by the European Regional Development Fund and Welsh Government (Ser Cymru programme – Project Sepsis).

Glucose supply and glycolysis inhibition shape the clinical fate of Staphylococcus epidermidis-infected preterm newborns

Preterm infants are susceptible to bloodstream infection by coagulase-negative staphylococci (CONS) that can lead to sepsis. High parenteral glucose supplement is commonly used to support their growth and energy expenditure, but may exceed endogenous regulation during infection, causing dysregulated immune response and clinical deterioration. Using a preterm piglet model of neonatal CONS sepsis induced by Staphylococcus epidermidis infection, we demonstrate the delicate interplay between immunity and glucose metabolism to regulate the host infection response. Circulating glucose levels, glycolysis and inflammatory response to infection are closely connected across the states of tolerance, resistance and immunoparalysis. Further, high parenteral glucose provision during infection induces hyperglycemia, elevated glycolysis and inflammation, leading to metabolic acidosis and sepsis, whereas glucose restricted individuals are clinically unaffected with increased gluconeogenesis to maintain moderate hypoglycemia. Finally, standard glucose supply maintaining normoglycemia or pharmacological glycolysis inhibition enhances bacterial clearance and dampens inflammation but fails to prevent sepsis. Our results uncover how blood glucose and glycolysis controls circulating immune responses, in turn determining the clinical fate of CONS infected preterm individuals. This questions the current practice of parenteral glucose supply for preterm infants during infection.

A place for neutrophils in the beneficial pathogen-agnostic effects of the BCG vaccine

The BCG vaccine has long been recognized for reducing the risk to suffer from infectious diseases unrelated to its target disease, tuberculosis. Evidence from human trials demonstrate substantial reductions in all-cause mortality, especially in the first week of life. Observational studies have identified an association between BCG vaccination and reduced risk of respiratory infectious disease and clinical malaria later in childhood. The mechanistic basis for these pathogen-agnostic benefits, also known as beneficial non-specific effects (NSE) of BCG have been attributed to trained immunity, or epigenetic reprogramming of hematopoietic cells that give rise to innate immune cells responding more efficiently to a broad range of pathogens. Furthermore, within trained immunity, the focus so far has been on enhanced monocyte function. However, polymorphonuclear cells, namely neutrophils, are not only major constituents of the hematopoietic compartment but functionally as well as numerically represent a prominent component of the immune system. The beneficial NSEs of the BCG vaccine on newborn sepsis was recently demonstrated to be driven by a BCG-mediated numeric increase of neutrophils (emergency granulopoiesis (EG)). And experimental evidence in animal models suggest that BCG can modulate neutrophil function as well. Together, these findings suggest that neutrophils are crucial to at least the immediate beneficial NSE of the BCG vaccine. Efforts to uncover the full gamut of mechanisms underpinning the broad beneficial effects of BCG should therefore include neutrophils at the forefront.

Neonatal Sepsis and Hemostasis

Neonatal sepsis is considered critical for a significant increase in neonatal morbidity and mortality among hospitalized neonates. Neonatal sepsis, in most cases, coexists with coagulopathy, which can prove to be life-threatening. Complex molecular and cellular systems are involved in the cross-talk between inflammation and hemostasis during sepsis. Disturbances in the regulating systems of the vascular endothelium, and platelet–endothelial and platelet–neutrophil interactions play a pivotal role in both inflammation and coagulation. This complex process is poorly understood in neonates. In addition to the developmental maturation of hemostasis and the immune response in neonatal sepsis, a cellular model of hemostasis during sepsis should be taken into account. This review focused on the molecular and cellular mechanisms underlying inflammation and hemostasis during neonatal sepsis, taking the developmental immune response and developmental hemostasis into account in order to provide future diagnostic approaches to be applied in everyday clinical settings. Regarding the diagnostic modalities, we briefly provide the limitations of the currently used conventional coagulation assays, focusing on viscoelastic tests and platelet flow cytometry.

A role for metabolism in determining neonatal immune function

Immune responses of neonates differ markedly to those of adults, with skewed cytokine phenotypes, reduced inflammatory properties and drastically diminished memory function. Recent research efforts have started to unravel the role of cellular metabolism in determining immune cell fate and function. For studies in humans, much of the work on metabolic mechanisms underpinning innate and adaptive immune responses by different haematopoietic cell types is in adults. Studies investigating the contribution of metabolic adaptation in the unique setting of early life are just emerging, and much more work is needed to elucidate the contribution of metabolism to neonatal immune responses. Here, we discuss our current understanding of neonatal immune responses, examine some of the latest developments in neonatal immunometabolism and consider the possible role of altered metabolism to the distinctive immune phenotype of the neonate. Understanding the role of metabolism in regulating immune function at this critical stage in life has direct benefit for the child by affording opportunities to maximize immediate and long-term health. Additionally, gaining insight into the diversity of human immune function and naturally evolved immunometabolic strategies that modulate immune function could be harnessed for a wide range of opportunities including new therapeutic approaches.

Lactiplantibacillus plantarum-Nomad and Ideal Probiotic

Probiotics are increasingly recognized as capable of positively modulating several aspects of human health. There are numerous attributes that make an ideal probiotic. Lactiplantibacillus plantarum (Lp) exhibits an ecological and metabolic flexibility that allows it to thrive in a variety of environments. The present review will highlight the genetic and functional characteristics of Lp that make it an ideal probiotic and summarizes the current knowledge about its potential application as a prophylactic or therapeutic intervention.

Potential Benefits of Bovine Colostrum in Pediatric Nutrition and Health

Bovine colostrum (BC), the first milk produced from cows after parturition, is increasingly used as a nutritional supplement to promote gut function and health in other species, including humans. The high levels of whey and casein proteins, immunoglobulins (Igs), and other milk bioactives in BC are adapted to meet the needs of newborn calves. However, BC supplementation may improve health outcomes across other species, especially when immune and gut functions are immature in early life. We provide a review of BC composition and its effects in infants and children in health and selected diseases (diarrhea, infection, growth-failure, preterm birth, necrotizing enterocolitis (NEC), short-bowel syndrome, and mucositis). Human trials and animal studies (mainly in piglets) are reviewed to assess the scientific evidence of whether BC is a safe and effective antimicrobial and immunomodulatory nutritional supplement that reduces clinical complications related to preterm birth, infections, and gut disorders. Studies in infants and animals suggest that BC should be supplemented at an optimal age, time, and level to be both safe and effective. Exclusive BC feeding is not recommended for infants because of nutritional imbalances relative to human milk. On the other hand, adverse effects, including allergies and intolerance, appear unlikely when BC is provided as a supplement within normal nutrition guidelines for infants and children. Larger clinical trials in infant populations are needed to provide more evidence of health benefits when patients are supplemented with BC in addition to human milk or formula. Igs and other bioactive factors in BC may work in synergy, making it critical to preserve bioactivity with gentle processing and pasteurization methods. BC has the potential to become a safe and effective nutritional supplement for several pediatric subpopulations.

Influence of innate immune activation on endocrine and metabolic pathways in infancy

Prematurity is the leading cause of neonatal morbidity and mortality worldwide. Premature infants often require extended hospital stays, with increased risk of developing infection compared with term infants. A picture is emerging of wide-ranging deleterious consequences resulting from innate immune system activation in the newborn infant. Those who survive infection have been exposed to a stimulus that can impose long-lasting alterations into later life. In this review, we discuss sepsis-driven alterations in integrated neuroendocrine and metabolic pathways and highlight current knowledge gaps in respect of neonatal sepsis. We review established biomarkers for sepsis and extend the discussion to examine emerging findings from human and animal models of neonatal sepsis that propose novel biomarkers for early identification of sepsis. Future research in this area is required to establish a greater understanding of the distinct neonatal signature of early and late-stage infection, to improve diagnosis, curtail inappropriate antibiotic use, and promote precision medicine through a biomarker-guided empirical and adjunctive treatment approach for neonatal sepsis. There is an unmet clinical need to decrease sepsis-induced morbidity in neonates, to limit and prevent adverse consequences in later life and decrease mortality.

Subclinical necrotizing enterocolitis-induced systemic immune suppression in neonatal preterm pigs

Preterm infants are at high risks of sepsis and necrotizing enterocolitis (NEC). Some develop sepsis shortly after suspected or confirmed NEC, implying that NEC may predispose to sepsis but the underlying mechanisms are unknown. Using NEC-sensitive preterm pigs as models, we investigated the immune status in animals following development of subclinical NEC-like lesions with variable severities. Caesarean-delivered preterm pigs were reared until day 5 or day 9. Blood was analyzed for T-cell subsets, neutrophil phagocytosis, transcriptomics, and immune responses to in vitro LPS challenge. Gut tissues were used for histology and cytokine analyses. Pigs with/without macroscopic NEC lesions were scored as healthy, mild, or severe NEC. Overall NEC incidence was similar on day 5 and day 9 (61%-62%) but with lower severity on day 9, implying gradual mucosal repair following the early phase of NEC. Pigs with NEC showed decreased goblet cell density and increased MPO⁺ and CD3⁺ cell infiltration in the distal small intestine or colon. Mild or severe NEC lesions had limited effects on circulating parameters on day 5. On day 9, pigs with NEC lesions (especially severe lesions) showed systemic immune suppression, as indicated by elevated Treg frequency, impaired neutrophil phagocytosis, low expression of genes related to innate immunity and Th1 polarization, and diminished LPS-induced immune responses. In conclusion, we shows evidence for NEC-induced systemic immune suppression, even with mild and subclinical NEC lesions. The results help to explain that preterm infants suffering from NEC may show high sensitivity to later secondary infections and sepsis.NEW & NOTEWORTHY Necrotizing enterocolitis (NEC) and sepsis are common diseases in preterm infants. Many develop sepsis following an episode of suspected NEC, suggesting NEC as a predisposing factor for sepsis but mechanisms are unclear. Using preterm pigs as a model, now we show that subclinical NEC lesions, independent of clinical confounding factors, induces systemic immune suppression. The results may help to explain the increased risks of infection and sepsis in preterm infants with previous NEC diagnosis.

One vaccine for life: Lessons from immune ontogeny

There remains a general misconception that the immune status of the fetus and neonate is immature or insufficient. However, emerging research in immune ontogeny prompts reconsideration of this orthodoxy, reframing this period instead as one of unique opportunity. Vaccine responses (qualitative and quantitative) vary between individuals, and across demographic cohorts. Elements of baseline immune status and function predict vaccine response - some of these factors are well described, others remain a subject of ongoing research, especially with the rapidly expanding field of 'omics' research, enabled by development of highly granular immune profiling techniques and increasing computational capacity. Age is one of the strongest predictive factors associated with variability in the response to vaccination; and predictable variation in response to vaccination is a key to identify the crucial underlying mechanisms. Specifically, circulating maternal antibody in the young infant can modulate immune response to vaccination, acting as an 'undercover adjuvant' that, counter to current dogma, may offer a pathway to longer lasting, higher quality immune response to vaccination. Exciting avenues for novel research in this area have the potential to dramatically alter how we protect the world's most vulnerable population - the very young.

Plasma Metabolomics to Evaluate Progression of Necrotising Enterocolitis in Preterm Pigs

Necrotising enterocolitis (NEC) is a microbiome-dependent gut disease in preterm infants in early life. Antibiotic treatment is a common intervention for NEC. How NEC lesions, with or without antibiotics, affect plasma metabolome was explored in this study. Formula-fed preterm pigs were used as a model for human NEC and treated with saline, parenteral or oral antibiotics (n = 15-17) for four days after delivery. Gut tissues were collected for evaluation of NEC-like lesions and plasma for metabolomic analysis by proton nuclear magnetic resonance spectroscopy (¹H-NMR). Metabolites were annotated, quantified and subjected to statistical modelling to delineate the effects of NEC and antibiotic treatment. Presence of severe NEC lesions, not antibiotic treatment, was the main drive for plasma metabolite changes. Relative to other pigs, pigs with severe NEC lesions had higher levels of alanine, histidine and myo-inositol, and lower levels of 3-hydroxybutyric acid and isobutyric acid. Across NEC lesion states (healthy, mild, severe), antibiotics directly affected only a few metabolites (tryptophan, 3-phenyllactic acid). Together and independently, NEC and antibiotic treatment affected circulating metabolites in preterm pigs. Amino acids and plasma metabolites, partly related to the gut microbiome, may be helpful to monitor progression of NEC lesions after proper validation.

Prenatal Immunity and Influences on Necrotizing Enterocolitis and Associated Neonatal Disorders

Prior to birth, the neonate has limited exposure to pathogens. The transition from the intra-uterine to the postnatal environment initiates a series of complex interactions between the newborn host and a variety of potential pathogens that persist over the first few weeks of life. This transition is particularly complex in the case of the premature and very low birth weight infant, who may be susceptible to many disorders as a result of an immature and underdeveloped immune system. Chief amongst these disorders is necrotizing enterocolitis (NEC), an acute inflammatory disorder that leads to necrosis of the intestine, and which can affect multiple systems and have the potential to result in long term effects if the infant is to survive. Here, we examine what is known about the interplay of the immune system with the maternal uterine environment, microbes, nutritional and other factors in the pathogenesis of neonatal pathologies such as NEC, while also taking into consideration the effects on the long-term health of affected children.

Impaired Neonatal Immunity and Infection Resistance Following Fetal Growth Restriction in Preterm Pigs

Background: Infants born preterm or small for gestational age (SGA, due to fetal growth restriction) both show an increased risk of neonatal infection. However, it remains unclear how the co-occurrence of preterm birth and SGA may affect neonatal immunity and infection risk. We hypothesized that fetal growth restricted (FGR) preterm newborns possess impaired immune competence and increased susceptibility to systemic infection and sepsis, relative to corresponding normal birth weight (NBW) newborns.

Methods: Using preterm pigs as a model for preterm infants, gene expression in lipopolysaccharide (LPS) stimulated cord blood was compared between NBW and FGR (lowest 25% birth weight percentile) preterm pigs. Next, clinical responses to a systemic Staphylococcus epidermidis (SE) challenge were investigated in newborn FGR and NBW preterm pigs. Finally, occurrence of spontaneous infections were investigated in 9 d-old FGR and NBW preterm pigs, with or without neonatal antibiotics treatment.

Results: At birth, preterm FGR piglets showed diminished ex vivo cord blood responses to LPS for genes related to both innate and adaptive immunity, and also more severe septic responses following SE infection (e.g., higher blood lactate, decreased blood pH, neutrophil and platelet counts, relative to NBW pigs). After 9 d, FGR pigs had higher incidence and severity of spontaneous infections (e.g., higher bacterial densities in the bone marrow), increased regulatory T cell numbers, reduced neutrophil phagocytosis capacity, and impaired ex vivo blood gene responses to LPS, especially when receiving neonatal antibiotics.

Conclusion: FGR at preterm birth is associated with poor immune competence, impaired infection resistance, and greater sepsis susceptibility in the immediate postnatal period. Our results may explain the increased morbidity and mortality of SGA preterm infants and highlight the need for clinical vigilance for this highly sensitive subgroup of preterm neonates.

Immunometabolic approaches to prevent, detect, and treat neonatal sepsis

The first days of postnatal life are energetically demanding as metabolic functions change dramatically to accommodate drastic environmental and physiologic transitions after birth. It is increasingly appreciated that metabolic pathways are not only crucial for nutrition but also play important roles in regulating inflammation and the host response to infection. Neonatal susceptibility to infection is increased due to a functionally distinct immune response characterized by high reliance on innate immune mechanisms. Interactions between metabolism and the immune response are increasingly recognized, as changes in metabolic pathways drive innate immune cell function and activation and consequently host response to pathogens. Moreover, metabolites, such as acetyl-coenzyme A (acetyl-CoA) and succinate have immunoregulatory properties and serve as cofactors for enzymes involved in epigenetic reprogramming or "training" of innate immune cells after an initial infectious exposure. Highly sensitive metabolomic approaches allow us to define alterations in metabolic signatures as they change during ontogeny and as perturbed by immunization or infection, thereby linking metabolic pathways to immune cell effector functions. Characterizing the ontogeny of immunometabolism will offer new opportunities to prevent, diagnose, and treat neonatal sepsis.

Prenatal inflammation suppresses blood Th1 polarization and gene clusters related to cellular energy metabolism in preterm newborns

Chorioamnionitis (CA, fetal membrane inflammation) predisposes to preterm birth and is associated with increased neonatal infection risk, but the separate effects of prematurity, CA, and postnatal adaptations on this risk are unclear. Using pigs as models for infants, we examined the systemic immune-metabolic status in cesarean-delivered preterm pigs, with and without CA induced by intra-amniotic (IA) LPS exposure. At birth, cord blood of preterm pigs showed neutropenia and low expressions of innate and adaptive immune genes, relative to term pigs. IA LPS induced CA and fetal systemic innate immune activation via complement and neutrophil-related pathways. These were mainly modulated via cellular regulations rather than granulopoiesis, as validated by the in vitro LPS stimulation of cord blood. After birth, IA LPS-exposed preterm pigs did not follow normal immune-metabolic ontogenies found in fetuses or newborns without prenatal insults, but showed consistently high levels of Treg, impaired Th1 polarization, and reduced expressions of multiple genes related to cellular oxidative phosphorylation and ribosomal activities. In conclusion, our results provide cellular and molecular evidence for CA-induced distinct neonatal immune-metabolic status with increased disease tolerance strategy, suggesting mechanisms for the clinical observation of elevated sepsis risks in immune-compromised preterm infants born with CA.

Growth Restriction and Systemic Immune Development in Preterm Piglets

Background: Many preterm infants are born with growth restriction (GR) following maternal or fetal complications before birth. Such infants may continue to grow slowly after birth, regardless of birth weight (BW), due to morbidities related to their immature organs. Severe GR increases the susceptibility to infections, but it is not clear if this is a consequence of impaired systemic immunity or other factors, such as prolonged hospital stay or poor mucosal barrier function. Using preterm pigs as models for preterm infants, we hypothesized that moderate GR, exerting limited clinical effects, does not influence systemic immune development.

Methods: Preterm pigs were delivered by cesarean section and fed bovine milk diets until 19 d. Piglets with fetal growth restriction (F-GR, the lowest 25% of BW, n = 27, excluding those with BW <350 g) and postnatal growth restriction (P-GR, the lowest 25% of postnatal growth rate, n = 24) were compared with their corresponding controls (F-CON, n = 92, and P-CON, n = 85, respectively). Organ weights were determined and blood collected for assessment of clinical status (blood chemistry and hematology). For a subgroup (n = 58), in depth analyses of neutrophil function, T cell counts, plasma cytokine levels, and leucocyte gene expression were performed.

Results: For F-GR pigs, adrenal gland weight was increased and bone mineral content decreased at 19 d. Total leucocyte levels were lower at birth and interleukin-10 levels increased at d 8–10. In P-GR pigs, total leucocyte, neutrophil, monocyte, and eosinophil counts along with helper T cell fractions were elevated at 8–19 d of age, while the fraction of neutrophils with phagocytic capacity was reduced. Diarrhea and all remaining organ weights, blood chemistry, and immune variables were not affected by F-GR or P-GR.

Conclusion: Moderate GR before and after preterm birth has limited effect on systemic immune development in preterm pigs, despite marginal effects on immune cell populations, adrenocortical function, and body composition. Similar responses may be observed for preterm infants with moderate fetal and postnatal growth restriction.

Association of Pertussis Toxin with Severe Pertussis Disease

Pertussis, caused by respiratory tract infection with the bacterial pathogen Bordetella pertussis, has long been considered to be a toxin-mediated disease. Bacteria adhere and multiply extracellularly in the airways and release several toxins, which have a variety of effects on the host, both local and systemic. Predominant among these toxins is pertussis toxin (PT), a multi-subunit protein toxin that inhibits signaling through a subset of G protein-coupled receptors in mammalian cells. PT activity has been linked with severe and lethal pertussis disease in young infants and a detoxified version of PT is a common component of all licensed acellular pertussis vaccines. The role of PT in typical pertussis disease in other individuals is less clear, but significant evidence supporting its contribution to pathogenesis has been accumulated from animal model studies. In this review we discuss the evidence indicating a role for PT in pertussis disease, focusing on its contribution to severe pertussis in infants, modulation of immune and inflammatory responses to infection, and the characteristic paroxysmal cough of pertussis.

Vascular Endothelium in Neonatal Sepsis: Basic Mechanisms and Translational Opportunities

Neonatal sepsis remains a major health issue worldwide, especially for low-birth weight and premature infants, with a high risk of death and devastating sequelae. Apart from antibiotics and supportive care, there is an unmet need for adjunctive treatments to improve the outcomes of neonatal sepsis. Strong and long-standing research on adult patients has shown that vascular endothelium is a key player in the pathophysiology of sepsis and sepsis-associated organ failure, through a direct interaction with pathogens, leukocytes, platelets, and the effect of soluble circulating mediators, in part produced by endothelial cells themselves. Despite abundant evidence that the neonatal immune response to sepsis is distinct from that of adults, comparable knowledge on neonatal vascular endothelium is much more limited. Neonatal endothelial cells express lower amounts of adhesion molecules compared to adult ones, and present a reduced capacity to neutralize reactive oxygen species. Conversely, available evidence on biomarkers of endothelial damage in neonates is not as robust as in adult patients, and endothelium-targeted therapeutic opportunities for neonatal sepsis are almost unexplored. Here, we summarize current knowledge on the structure of neonatal vascular endothelium, its interactions with neonatal immune system and possible endothelium-targeted diagnostic and therapeutic tools for neonatal sepsis. Furthermore, we outline areas of basic and translational research worthy of further study, to shed light on the role of vascular endothelium in the context of neonatal sepsis.