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

Regulation of host metabolism and defense strategies to survive neonatal infection

Two distinct defense strategies, disease resistance (DR) and disease tolerance (DT), enable a host to survive infectious diseases. Newborns, constrained by limited energy reserves, predominantly rely on DT to cope with infection. However, this approach may fail when pathogen levels surpass a critical threshold, prompting a shift to DR that can lead to dysregulated immune responses and sepsis. The mechanisms governing the interplay between DR and DT in newborns remain poorly understood. Here, we compare metabolic traits and defense strategies between survivors and non-survivors in Staphylococcus epidermidis (S. epidermidis)-infected preterm piglets, mimicking infection in preterm infants. Compared to non-survivors, survivors displayed elevated DR during the initial phase of infection, followed by stronger DT in later stages. In contrast, non-survivors showed clear signs of respiratory and metabolic acidosis and hyperglycemia, together with exaggerated inflammation and organ dysfunctions. Hepatic transcriptomics revealed a strong association between the DT phenotype and heightened oxidative phosphorylation in survivors, coupled with suppressed glycolysis and immune signaling. Plasma metabolomics confirmed the findings of metabolic regulations associated with DT phenotype in survivors. Our study suggests a significant association between the initial DR and subsequent DT, which collectively contributes to improved infection survival. The regulation of metabolic processes that optimize the timing and balance between DR and DT holds significant potential for developing novel therapeutic strategies for neonatal infection.

Alterations in maternal-fetal gut and amniotic fluid microbiota associated with fetal growth restriction

BACKGROUND

Fetal growth restriction (FGR) is typically characterised as the fetus' inability to reach its inherent growth potential. A growing body of evidence points to the important role of the maternal gut microbiota in FGR development. However, comprehensive research on changes in maternal-fetal gut and intrauterine microbiota related to FGR is lacking.

METHODS

In this case-control study, we sequenced bacterial 16S rRNA from 35 maternal faecal, 35 meconium, and 31 amniotic fluid samples collected from 19 pregnant women diagnosed with FGR and 16 healthy controls. We identified putative bacterial taxonomic and functional characteristics associated with FGR by comparing these to control samples.

RESULTS

We identified 34 differential operational taxonomic units (OTUs) in amniotic fluid, seven differential OTUs in maternal faecal matter, and two differential OTUs in meconium. Compared to controls, FGR subjects exhibited enriched bacterial OTUs of the genus Bacteroides in the maternal gut. They also had depleted OTUs of the order Enterobacterales and genus Pseudomonas in the amniotic fluid and genus Stenotrophomonas in the fetal gut. These altered bacterial OTUs showed a significant correlation with neonatal weight and fetal ultrasonographic indexes. Additionally, we identified differential microbial functional pathways related to glycan and lipid metabolism in the maternal gut. We developed diagnostic biomarkers for FGR based on the maternal-fetal gut and amniotic fluid microbiota.

CONCLUSIONS

This study offers a comprehensive overview of the shifts in microbial composition and functional pathways in the maternal-fetal gut and amniotic fluid microbiota related to FGR, and present novel insights into the development and screening of FGR. However, the assessment of contamination's impact on meconium and amniotic fluid remains inconclusive, necessitating further rigorous experimentation to address this scientific inquiry in future studies.

Insulin-like growth factor-1 effects on kidney development in preterm piglets

BACKGROUND

Preterm birth disrupts fetal kidney development, potentially leading to postnatal acute kidney injury. Preterm infants are deficient in insulin-like growth factor 1 (IGF-1), a growth factor that stimulates organ development. By utilizing a preterm pig model, this study investigated whether IGF-1 supplementation enhances preterm kidney maturation.

METHODS

Cesarean-delivered preterm pigs were treated systemically IGF-1 or vehicle control for 5, 9 or 19 days after birth. Blood, urine, and kidney tissue were collected for biochemical, histological and gene expression analyses. Age-matched term-born pigs were sacrificed at similar postnatal ages and served as the reference group.

RESULTS

Compared with term pigs, preterm pigs exhibited impaired kidney maturation, as indicated by analyses of renal morphology, histopathology, and inflammatory and injury markers. Supplementation with IGF-1 reduced signs of kidney immaturity, particularly in the first week of life, as indicated by improved morphology, upregulated expression of key developmental genes, reduced severity and incidence of microscopic lesions, and decreased levels of inflammatory and injury markers. No association was seen between the symptoms of necrotizing enterocolitis and kidney defects.

CONCLUSION

Preterm birth in pigs impairs kidney maturation and exogenous IGF-1 treatment partially reverses this impairment. Early IGF-1 supplementation could support the development of preterm kidneys.

IMPACT

Preterm birth may disrupt kidney development in newborns, potentially leading to morphological changes, injury, and inflammation. Preterm pigs have previously been used as models for preterm infants, but not for kidney development. IGF-1 supplementation promotes kidney maturation and alleviates renal impairments in the first week of life in preterm pigs. IGF-1 may hold potential as a supportive therapy for preterm infants sensitive to acute kidney injury.

A Gently Processed Skim Milk-Derived Whey Protein Concentrate for Infant Formula: Effects on Gut Development and Immunity in Preterm Pigs

SCOPE

Processing of whey protein concentrate (WPC) for infant formulas may induce protein modifications with severe consequences for preterm newborn development. The study investigates how conventional WPC and a gently processed skim milk-derived WPC (SPC) affect gut and immune development after birth.

METHODS AND RESULTS

Newborn, preterm pigs used as a model of preterm infants were fed formula containing WPC, SPC, extra heat-treated SPC (HT-SPC), or stored HT-SPC (HTS-SPC) for 5 days. SPC contained no protein aggregates and more native lactoferrin, and despite higher Maillard reaction product (MRP) formation, the clinical response and most gut and immune parameters are similar to WPC pigs. SPC feeding negatively impacts intestinal MRP accumulation, mucosa, and bacterial diversity. In contrast, circulating T-cells are decreased and oxidative stress- and inflammation-related genes are upregulated in WPC pigs. Protein aggregation and MRP formation increase in HTS-SPC, leading to reduced antibacterial activity, lactase/maltase ratio, circulating neutrophils, and cytotoxic T-cells besides increased gut MRP accumulation and expression of TNFAIP3.

CONCLUSION

The gently processed SPC has more native protein, but higher MRP levels than WPC, resulting in similar tolerability but subclinical adverse gut effects in preterm pigs. Additional heat treatment and storage further induce MRP formation, gut inflammation, and intestinal mucosal damage.

Size matters: lower body weight pigs have a different response to immune challenge and amino acids supplementation above the estimated requirement compared to heavy pigs

The immune response varies between pigs, as not all pigs have the same response to a stressor. This variation may exist between individuals due to body weight (BW) or body composition, which may impact the capacity for coping with an immune challenge (IC). Tryptophan (Trp), threonine (Thr), and methionine (Met) requirements might also play a considerable part in supporting immune system activation while reducing variation between pigs; however, the latter has yet to be reported. This exploratory study investigated the effect of initial BW (light vs. heavy-weight) and supplementation of Trp, Thr, and Met above National Research Council (NRC) requirements on feeding behavior and the coping capacity of growing pigs under an IC. Eighty gilts were categorized into 2 groups according to BW: light-weight (LW, 22.5 kg) and heavy-weight pigs (HW, 28.5 kg). Both BW groups were group-housed for a 28-d trial in a good or poor sanitary condition (SC). Pigs within a poor SC were orally inoculated with 2 × 109 colony units of Salmonella Typhimurium, and fresh manure from a pig farm was spread on the floor. Pigs within good SC were not inoculated, nor was manure spread. Two diets were provided within each SC: control (CN) or supplemented (AA+) with Trp, Thr, and Met at 120% of NRC recommended levels. A principal component analysis was performed in R, and a feeding behavior index was calculated in SAS. Results showed that LW and HW pigs were clustered separately on day 0, where LW pigs had a positive correlation with body lipid percentage (r = 0.83), and HW pigs had a positive correlation with body protein percentage (r = 0.75). After the IC, the cluster configuration changed, with diets influencing LW more than HW pigs within poor SC. On day 14, LW fed AA + diet in poor SC was clustered separately from LW pigs fed CN diet, whereas LW fed AA + and CN diets in good SC were clustered together. For feeding behavior, in both analyzed periods (period 1: days 7 to 14; period 2: days 21 to 28), LW had lower total feed intake and shorter meals than HW pigs (P < 0.10), independent of the SC. Furthermore, LW pigs fed AA + diet had a more regular feed intake pattern than those fed CN diet, while a more irregular pattern was observed for HW pigs fed AA + diet than CN diet at period 2. These findings suggest that supplementing Trp, Thr, and Met above requirements may be a nutritional strategy for LW pigs under IC by improving feed intake regularity and reducing the probability of being susceptible to IC.

Factors Associated With Culture-proven Neonatal Sepsis and Resistance to First-line Antibiotics in Indonesia

BACKGROUND

Neonatal sepsis is one of the leading causes of neonatal morbidity and mortality in low- and middle-income countries. Blood culture positivity rates and antibiotic resistance pattern of neonatal sepsis differs across various regions. This study aims to identify clinical cofactors associated with blood culture-proven neonatal sepsis and in vitro resistance to first-line antibiotics (ampicillin and gentamicin) from cases originating in a tertiary healthcare center in Surabaya, Indonesia.

METHODS

A retrospective cohort study was conducted from January 2020 to August 2022 by utilizing secondary data collected from standardized electronic medical records. Microbiologic characteristics and associated factors were statistically analyzed using multivariable logistic regression.

RESULTS

Across 266 neonatal sepsis cases, 46.9% were culture-proven and 79.2% of confirmed sepsis were resistant to first-line antibiotics. The most common isolated pathogen is Klebsiella pneumoniae , followed by coagulase-negative Staphylococci , Acinetobacter baumannii and Enterobacter cloacae . Extremely preterm delivery [adjusted odds ratio (aOR): 5.813; 95% confidence interval (CI): 1.70-19.91] and late-onset sepsis (aOR: 9.165; 95% CI: 5.12-16.40) were associated with culture-proven neonatal sepsis. Increased odds of resistance to first-line antibiotics were identified in extremely preterm (<28 weeks) or very-preterm delivery (28 to <32 weeks) (aOR: 50.80; 95% CI: 1.66-1554.21 and aOR: 45.679; 95% CI: 3.22-647.46, respectively), cesarean section (aOR: 4.149; 95% CI: 1.04-16.53) and an absence of antenatal corticosteroid use (aOR: 0.233; 95% CI: 0.07-0.76).

CONCLUSIONS

The association between clinical cofactors with culture-proven sepsis and antibiotic resistance emphasizes the importance for clinicians to adjust empirical antibiotic regimens based on the local antibiogram and resource availability.

Insulin-like growth factor 1 associated with altered immune responses in preterm infants and pigs

BACKGROUND

Preterm infants show low blood levels of insulin-like growth factor 1 (IGF-1), known to be negatively correlated with Interleukin-6 (IL-6). We hypothesized that circulating IGF-1 is associated with systemic immune-markers following preterm birth and that exogenous IGF-1 supplementation modulates immune development in preterm pigs, used as model for preterm infants.

METHODS

Plasma levels of IGF-1 and 29 inflammatory markers were measured in very preterm infants (n = 221). In preterm pigs, systemic immune development, assessed by in vitro challenge, was compared between IGF-1 treated (2.25 mg/kg/day) and control animals.

RESULTS

Preterm infants with lowest gestational age and birth weight showed the lowest IGF-1 levels, which were correlated not only with IL-6, but a range of immune-markers. IGF-1 supplementation to preterm pigs reduced plasma IL-10 and Interferon-γ (IFN-γ), IL-2 responses to challenge and reduced expression of genes related to Th1 polarization. In vitro addition of IGF-1 (100 ng/mL) further reduced the IL-2 and IFN-γ responses but increased IL-10 response.

CONCLUSIONS

In preterm infants, plasma IGF-1 correlated with several immune markers, while supplementing IGF-1 to preterm pigs tended to reduce Th1 immune responses. Future studies should document whether IGF-1 supplementation to preterm infants affects immune development and sensitivity to infection.

IMPACT

Supplementation of insulin-like growth factor 1 (IGF-1) to preterm infants has been proposed to promote postnatal growth, but its impact on the developing immune system is largely unknown. In a cohort of very preterm infants, low gestational age and birth weight were the primary predictors of low plasma levels of IGF-1, which in turn were associated with plasma immune markers. Meanwhile, in immature preterm pigs, experimental supplementation of IGF-1 reduced Th1-related immune responses in early life. Supplementation of IGF-1 to preterm infants may affect the developing immune system, which needs consideration when evaluating overall impact on neonatal health.

A Comparison of Haematological and Biochemical Profiles between Intrauterine Growth Restriction and Normal Piglets at 72 Hours Postpartum

Intrauterine growth restriction in piglets has been a problem in the pig industry due to genetic selection based on hyperprolificacy. This has led to an increase in the number of underweight piglets and a worsening of the survival rate. The goal of this study was to enhance the knowledge of differences between normal and IUGR piglets a few hours after birth in terms of haematological variables, biochemical parameters, and immunoglobulin levels. Two groups of 20 piglets each were assessed. The control group (N) was made up of piglets with weights greater than 1500 g, and the IUGR group consisted of piglets weighing 500-1000 g and with at least two IUGR features. Blood samples were collected 72 h after birth for analysis of the red and white blood cell parameters, reticulocyte indices, platelet indices, biochemical parameters, and immunoglobulin levels. Alterations in red blood cells and reticulocytes, a lower lymphocyte count, hyperinsulinemia, and high oxidative stress were observed in IUGR piglets (p < 0.05). In contrast, differences were not observed (p > 0.05) in the serum immunoglobulin level. It can be concluded that the haematological and biochemical differences in IUGR piglets with respect to normal-weight piglets are present at birth indicating possible alterations in immunity, metabolism, and redox status; therefore, IUGR piglets could be more vulnerable to illness and future disorders, such as metabolic syndrome.

Neonatal prophylactic antibiotics after preterm birth affect plasma proteome and immune development in pigs

BACKGROUND

Most preterm infants receive antibiotics to prevent serious infections shortly after birth. However, prolonged antibiotic treatment predisposes to gut dysbiosis and late-onset sepsis. Using preterm pigs as model, we hypothesized that neonatal prophylactic antibiotics impair systemic immune development beyond the days of antibiotic treatment.

METHODS

Preterm pigs (90% gestation) were fed formula for 9 days, treated with sterile water (CON) or enteral antibiotics from day 1 to 4. On days 5 and 9, blood was collected for haematology, in vitro LPS stimulation, and plasma proteomics.

RESULTS

Antibiotic treatment altered the abundance of 21 and 47 plasma proteins on days 5 and 9, representing 6.6% and 14.8% of the total annotated proteins, respectively. Most antibiotics-induced proteome changes related to complement cascade, neutrophil degranulation, and acute phase responses. Neutrophil and lymphocyte counts were higher in antibiotics-treated pigs on day 5 but did not change from days 5-9, in contrast to increasing cell counts in CON. The antibiotics treatment suppressed TNF-alpha and IL-10 responses to in vitro LPS challenge on day 5, 7 and 9.

CONCLUSION

Few days of antibiotics treatment following preterm birth alter the plasma proteome and inhibit systemic immune development, even beyond the days of treatment.

IMPACT

1. Neonatal prophylactic antibiotics alter the plasma proteome and suppress systemic immune development in preterm pigs 2. The effects of prophylactic antibiotics last beyond the days of treatment. 3. Neonatal antibiotics treatment for compromised human newborns may predispose to longer-term risks of impaired immunity and infections.

Release of HMGB1 and Toll-like Receptors 2, 4, and 9 Signaling Are Modulated by Bifidobacterium animalis subsp. lactis BB-12 and Salmonella Typhimurium in a Gnotobiotic Piglet Model of Preterm Infants

Gnotobiotic (GN) animals with defined microbiota allow us to study host-microbiota and microbiota-microbiota interferences. Preterm germ-free (GF) piglets were mono-associated with probiotic Bifidobacterium animalis subsp. lactis BB-12 (BB12) to ameliorate/prevent the consequences of infection with the Salmonella Typhimurium strain LT2 (LT2). Goblet cell density; expression of Toll-like receptors (TLRs) 2, 4, and 9; high mobility group box 1 (HMGB1); interleukin (IL)-6; and IL-12/23p40 were analyzed to evaluate the possible modulatory effect of BB12. BB12 prevented an LT2-induced decrease of goblet cell density in the colon. TLRs signaling modified by LT2 was not influenced by the previous association with BB12. The expression of HMGB1, IL-6, and IL12/23p40 in the jejunum, ileum, and colon and their levels in plasma were all decreased by BB12, but these changes were not statistically significant. In the colon, differences in HMGB1 distribution between the GF and LT2 piglet groups were observed. In conclusion, the mono-association of GF piglets with BB12 prior to LT2 infection partially ameliorated the inflammatory response to LT2 infection.

Insight into the long-term impact of birth weight on intestinal development, microbial settlement, and the metabolism of weaned piglets

Infant mortality of low birth body weight (LBBW) piglets can reach 10% and is mainly due to gut and immune system immaturity which can lead to a higher risk in the long term. This study aimed to assess the impact of birth body weight (BBW) on piglet metabolism, gut status, and microbial profile from weaning to 21 d postweaning. At birth, 32 piglets were selected for their BBW and inserted into the normal BBW (NBBW:1.38 ± 0.09 g) or the LBBW (0.92 ± 0.07 g) group. The piglets were weighed weekly from weaning (d0) to d21. At d9 and d21, 8 piglets/group were slaughtered to obtain the distal jejunum for morphology, immunohistochemistry, and gene expression analysis, colon content for microbiota and short-chain fatty acid (SCFA) analysis, and intestinal content for pH measurement. Blood was collected for metabolomic, haptoglobin (Hp), and reactive oxygen metabolite (ROM) analysis. The LBBW group had a lower body weight (BW) throughout the study (P < 0.01), a lower average daily gain from d9-d21 (P = 0.002), and lower feed intake (P = 0.02). The LBBW piglets had lower Hp at d9 (P = 0.03), higher ROMs at d21 (P = 0.06), and a net alteration of the amino acid (AA) metabolism at d9 and d21. A higher expression of NFKB2 was observed in the LBBW piglets at d9 (P = 0.003) and d21 (P < 0.001). MYD88 expression was enhanced in NBBW piglets at d9 (P < 0.001). The LBBW piglets had a lower villus height, absorptive mucosal surface (P = 0.01), and villus height:crypt depth ratio (P = 0.02), and a greater number of T-lymphocytes in both the epithelium and the crypts (P < 0.001) at d21. At d21, the LBBW piglets had higher lactic acid, acetate, butyrate, and valerate, and also higher SCFA in the colon (P < 0.05). The LBBW piglets had a higher Shannon index (P = 0.01) at d9 and a higher abundance of SCFA-fermenting bacteria. In conclusion, the present study confirmed that LBBW could impact the gut mucosal structure, immunity, and inflammatory and oxidative status, leading to an altered AA metabolism, and delaying the recovery from weaning.

Placental morphological features of small for gestational age preterm neonates born to mothers with pregnancy-induced hypertension

Introduction

Small for gestational age (SGA) neonates are often born to mothers with pregnancy-induced hypertension (PIH). Here, we aimed to explore the morphometric characteristics of the placenta during the perinatal period associated with SGA risk in mothers with PIH and identify the risk factors related to SGA.

Methods

The medical records of 134 neonates born between 28- and 32-weeks' gestation to PIH mothers were retrospectively analyzed. Placental morphology and umbilical cord (UC) length were compared between the SGA and appropriate for gestational age (AGA) groups.

Results

The placenta of the SGA group had a shorter major (15.00 vs. 18.00 cm; z = -6.04, p < 0.01) and minor placenta axes (13.00 vs. 15.00 cm; z = -4.59, p < 0.01), lower weight (300.00 vs. 420.00 g; z = -7.21, p < 0.01), smaller volume (282.00 vs. 396.00 cm³; z = -5.00, p < 0.01), and smaller area (141.00 vs. 212.00 cm²; z = -5.96, p < 0.01) than the AGA group. The UC was significantly shorter (39.00 vs. 44.00 cm; z = -3.68, p < 0.01). Short placental major axis [p = 0.03; odds ratio (OR): 2.16; 95% confidence interval (CI): 1.84 - 2.63] and low placental weight (p < 0.01; OR: 2.68; 95% CI: 2.66 - 2.70) were independent risk factors for SGA in premature newborns of PIH mothers.

Discussion

A major axis shorter than 15.5 cm or placental weight lower than 347.50 g at birth was related to a greater risk of SGA infants born to PIH mothers. As a predictor in prenatal ultrasound, the major axis is more helpful for precise prenatal pre-evaluation of vulnerable SGA preterm neonates with PIH mothers.

The role of interleukin-1 in perinatal inflammation and its impact on transitional circulation

Preterm birth is defined as delivery at <37 weeks of gestational age (GA) and exposes 15 million infants worldwide to serious early life diseases. Lowering the age of viability to 22 weeks GA entailed provision of intensive care to a greater number of extremely premature infants. Moreover, improved survival, especially at extremes of prematurity, comes with a rising incidence of early life diseases with short- and long-term sequelae. The transition from fetal to neonatal circulation is a substantial and complex physiologic adaptation, which normally happens rapidly and in an orderly sequence. Maternal chorioamnionitis or fetal growth restriction (FGR) are two common causes of preterm birth that are associated with impaired circulatory transition. Among many cytokines contributing to the pathogenesis of chorioamnionitis-related perinatal inflammatory diseases, the potent pro-inflammatory interleukin (IL)-1 has been shown to play a central role. The effects of utero-placental insufficiency-related FGR and in-utero hypoxia may also be mediated, in part, via the inflammatory cascade. In preclinical studies, blocking such inflammation, early and effectively, holds great promise for improving the transition of circulation. In this mini-review, we outline the mechanistic pathways leading to abnormalities in transitional circulation in chorioamnionitis and FGR. In addition, we explore the therapeutic potential of targeting IL-1 and its influence on perinatal transition in the context of chorioamnionitis and FGR.

Functional amino acid supplementation postweaning mitigates the response of normal birth weight more than for low birth weight pigs to a subsequent Salmonella challenge

Previous work has shown that dietary supplementation with key functional amino acids (FAA) improves growth performance and immune status of disease-challenged normal birth weight (NBW) pigs. It is not known whether FAA supplementation attenuates the effects of a subsequent disease challenge or whether this response is similar in low birth weight (LBW) pigs. The objective was to determine the effects of birth weight and FAA supplementation during the postweaning period in Salmonella-challenged pigs. Thirty-two LBW (1.08 ± 0.11 kg) and NBW (1.58 ± 0.11 kg) pigs were assigned to a nursery feeding program at weaning (25 d) for 31 days in a 2 × 2 factorial arrangement. Factors were birth weight category (LBW vs. NBW) and basal (FAA-) or supplemented FAA profile (FAA+; Thr, Met, and Trp at 120% of requirements). At d 31, pigs were placed onto a common grower diet and, after a 7-d adaptation period, were inoculated with Salmonella Typhimurium (ST; 2.2 × 10⁹ colony-forming units/mL) and monitored for 7-d postinoculation. Growth performance, rectal temperature, fecal score, indicators of gut health, ST shedding score in feces, intestinal ST colonization and translocation, and blood parameters of acute-phase response and antioxidant balance were measured pre- and postinoculation. Inoculation with ST increased temperature and fecal score, and the overall rectal temperature was higher in LBW compared to NBW pigs (P < 0.05). Postinoculation (d 7), reduced:oxidized glutathione was increased in NBW compared to LBW pigs (P < 0.05). Salmonella shedding and translocation to spleen were lower in NBW-FAA+ compared to NBW-FAA- pigs (P < 0.05). Postinoculation average daily gain was higher in NBW-FAA+ (P < 0.05) compared to the other groups. Postinoculation haptoglobin, superoxide dismutase, and colonic myeloperoxidase were increased in LBW-FAA- pigs (P < 0.05). Ileal alkaline phosphatase was decreased in LBW compared to NBW (P < 0.05). Overall, FAA supplementation represents a potential strategy to mitigate the effect of enteric disease challenge in NBW, but not LBW pigs.

Regulatory T Cells: Angels or Demons in the Pathophysiology of Sepsis?

Sepsis is a syndrome characterized by life-threatening organ dysfunction caused by the dysregulated host response to an infection. Sepsis, especially septic shock and multiple organ dysfunction is a medical emergency associated with high morbidity, high mortality, and prolonged after-effects. Over the past 20 years, regulatory T cells (Tregs) have been a key topic of focus in all stages of sepsis research. Tregs play a controversial role in sepsis based on their heterogeneous characteristics, complex organ/tissue-specific patterns in the host, the multi-dimensional heterogeneous syndrome of sepsis, the different types of pathogenic microbiology, and even different types of laboratory research models and clinical research methods. In the context of sepsis, Tregs may be considered both angels and demons. We propose that the symptoms and signs of sepsis can be attenuated by regulating Tregs. This review summarizes the controversial roles and Treg checkpoints in sepsis.

Ventilation-Induced Lung Injury (VILI) in Neonates: Evidence-Based Concepts and Lung-Protective Strategies

Supportive care with mechanical ventilation continues to be an essential strategy for managing severe neonatal respiratory failure; however, it is well known to cause and accentuate neonatal lung injury. The pathogenesis of ventilator-induced lung injury (VILI) is multifactorial and complex, resulting predominantly from interactions between ventilator-related factors and patient-related factors. Importantly, VILI is a significant risk factor for developing bronchopulmonary dysplasia (BPD), the most common chronic respiratory morbidity of preterm infants that lacks specific therapies, causes life-long morbidities, and imposes psychosocial and economic burdens. Studies of older children and adults suggest that understanding how and why VILI occurs is essential to developing strategies for mitigating VILI and its consequences. This article reviews the preclinical and clinical evidence on the pathogenesis and pathophysiology of VILI in neonates. We also highlight the evidence behind various lung-protective strategies to guide clinicians in preventing and attenuating VILI and, by extension, BPD in neonates. Further, we provide a snapshot of future directions that may help minimize neonatal VILI.

Targeting the Toll-like receptor pathway as a therapeutic strategy for neonatal infection

Toll-like receptors (TLRs) are crucial transmembrane receptors that form part of the innate immune response. They play a role in the recognition of various microorganisms and their elimination from the host. TLRs have been proposed as vital immunomodulators in the regulation of multiple neonatal stressors that extend beyond infection such as oxidative stress and pain. The immune system is immature at birth and takes some time to become fully established. As such, babies are especially vulnerable to sepsis at this early stage of life. Findings suggest a gestational age-dependent increase in TLR expression. TLRs engage with accessory and adaptor proteins to facilitate recognition of pathogens and their activation of the receptor. TLRs are generally upregulated during infection and promote the transcription and release of proinflammatory cytokines. Several studies report that TLRs are epigenetically modulated by chromatin changes and promoter methylation upon bacterial infection that have long-term influences on immune responses. TLR activation is reported to modulate cardiorespiratory responses during infection and may play a key role in driving homeostatic instability observed during sepsis. Although complex, TLR signaling and downstream pathways are potential therapeutic targets in the treatment of neonatal diseases. By reviewing the expression and function of key Toll-like receptors, we aim to provide an important framework to understand the functional role of these receptors in response to stress and infection in premature infants.

Infant Formula Based on Milk Fat Affects Immune Development in Both Normal Birthweight and Fetal Growth Restricted Neonatal Piglets

Infant formulas offer an alternative to breast milk for both normal birth weight (NBW) and immunocompromised intrauterine growth restricted (IUGR) infants. Although the lipid fraction in formulas is often derived from vegetable oils, it is unclear if this alters immunological outcomes relative to milk fats or whether these effects differ between IUGR and NBW infants. We hypothesized that replacing vegetable oil with bovine milk fat in infant formula would improve immune development in IUGR and NBW neonates. Two-day old piglets were selected (NBW, n = 18, IUGR, n = 18) and each group of animals were fed formula based on either vegetable oil (VEG) or bovine milk fat (MILK). Animals were reared until day 23/24 and systemic immune parameters were evaluated. Milk-fat feeding decreased blood neutrophil counts and improved neutrophil function while transiently reducing leucocytes’ expression of genes related to adaptive and innate immunity as well as energy metabolism, following in vitro stimulation by live Staphylococcus epidermidis (whole blood, 2 h). However, there were only a few interactions between milk-fat type and birthweight status. Thus, piglets fed milk-fat-based formula had improved neutrophil maturation and suppressed pro-inflammatory responses, compared to those fed vegetable-oil-based formula.

Sex-Specific Survival, Growth, Immunity and Organ Development in Preterm Pigs as Models for Immature Newborns

Background: After very preterm birth, male infants show higher mortality than females, with higher incidence of lung immaturity, neurological deficits, infections, and growth failure. In modern pig production, piglets dying in the perinatal period (up to 20%) often show signs of immature organs, but sex-specific effects are not clear. Using preterm pigs as model for immature infants and piglets, we hypothesized that neonatal survival and initial growth and immune development depend on sex. Methods: Using data from a series of previous intervention trials with similar delivery and rearing procedures, we established three cohorts of preterm pigs (90% gestation), reared for 5, 9, or 19 days before sample collection (total n = 1,938 piglets from 109 litters). Partly overlapping endpoints among experiments allowed for multiple comparisons between males and females for data on mortality, body and organ growth, gut, immunity, and brain function. Results: Within the first 2 days, males showed higher mortality than females (18 vs. 8%, P < 0.001), but less severe immune response to gram-positive infection. No effect of sex was observed for thermoregulation or plasma cortisol. Later, infection resistance did not differ between sexes, but growth rate was reduced for body (up to -40%) and kidneys (-6%) in males, with higher leucocyte counts (+15%) and lower CD4 T cell fraction (-5%) on day 9 and lower monocyte counts (-18%, day 19, all P < 0.05). Gut structure, function and necrotizing enterocolitis (NEC) incidence were similar between groups, but intestinal weight (-3%) and brush-border enzyme activities were reduced at day 5 (lactase, DPP IV, -8%) in males. Remaining values for blood biochemistry, hematology, bone density, regional brain weights, and visual memory (tested in a T maze) were similar. Conclusion: Following preterm birth, male pigs show higher mortality and slower growth than females, despite limited differences in organ growth, gut, immune, and brain functions. Neonatal intensive care procedures may be particularly important for compromised newborns of the male sex. Preterm pigs can serve as good models to study the interactions of sex- and maturation-specific survival and physiological adaptation in mammals.

Radiographic Imaging to Evaluate Food Passage Rate in Preterm Piglets as a Model for Preterm Infants

Objectives and study: Gut motility in infants mature with increasing post-menstrual age and is affected by numerous hormonal, immunological and nutritional factors. However, it remains unclear how age and diet influence gut motility and its relation to feeding intolerance and gastric residuals in preterm neonates. Using preterm piglets as a model for infants, we investigated if contrast passage rate, as determined by X-ray contrast imaging, is affected by gestational age at birth, advancing postnatal age and different milk diets. Methods: Contrast passage rate was evaluated using serial abdominal X-ray imaging on postnatal day 4 and 18 in preterm and near-term piglets fed infant formula, colostrum or intact bovine milk, with or without added fortifier (total n = 140). Results: Preterm piglets had a faster small intestinal passage rate of contrast solution at day 4 of life than near-term piglets (SIEmpty, hazard ratio (HR): 0.52, 95%CI [0.15, 0.88], p < 0.01). Formula fed piglets at day 4 had a faster passage rate of contrast to caecum (ToCecum, HR: 0.61, 95%CI [0.25,0.96], p = 0.03), and through the colon region (CaecumToRectum, p < 0.05, day 4) than colostrum fed preterm piglets. The time for contrast to leave the stomach, and passage through the colon in day 4 preterm piglets were slower than in older piglets at day 18 (both, p < 0.05). Adding a nutrient fortifier increased body growth, gastric residuals, intestinal length and weight, but did not affect any of the observed passage rates of the contrast solution. Conclusion: Serial X-ray contrast imaging is a feasible method to assess food passage rate in preterm piglets. Contrast passage rate through different gut segments is affected by gestational age at birth, postnatal age, and milk diet. The preterm piglet could be a good model to investigate clinical and dietary factors that support maturation of gut motility and thereby feeding tolerance and gut health in preterm infants.