Responses In Early Life Research Articles

Neonatal Immunity to Bordetella pertussis Infection and Current Prevention Strategies.

Bordetella pertussis is the bacterial agent of whooping cough, an infectious disease that is reemerging despite high vaccine coverage. Newborn children are the most affected, not only because they are too young to be vaccinated but also due to qualitative and quantitative differences in their immune system, which makes them more susceptible to infection and severe manifestations, leading to a higher mortality rate comparing to other groups. Until recently, prevention consisted of vaccinating children in the first year of life and the herd vaccination of people directly in touch with them, but the increase in cases demands more effective strategies that can overcome the developing immune response in early life and induce protection while children are most vulnerable.

Understanding the Functional Properties of Neonatal Dendritic Cells: A Doorway to Enhance Vaccine Effectiveness?

Increased susceptibility to infectious diseases is a hallmark of the neonatal period of life that is generally attributed to a relative immaturity of the immune system. Dendritic cells (DCs) are innate immune sentinels with vital roles in the initiation and orchestration of immune responses, thus, constituting a promising target for promoting neonatal immunity. However, as is the case for other immune cells, neonatal DCs have been suggested to be functionally immature compared to their adult counterparts. Here we review some of the unique aspects of neonatal DCs that shape immune responses in early life and speculate whether the functional properties of neonatal DCs could be exploited or manipulated to promote more effective vaccination in early life.

Neonate-omics: Charting the Unknown Immune Response in Early Life

The study of neonatal immunology has been hampered by lack of access to infant samples. Novel sample sparing methods and systems-wide approaches have uniquely expanded this field, demonstrating that newborn immunity varies widely but converges over the first 3months of life. During this important time window, environmental and genetic factors impact the infant immune system and can influence lifelong immunity.

Prenatal Exposure to Perfluoroalkyl Substances and Isomers Link to Depressed Toxoid Antibody Responses in Early Childhood: Guangzhou Birth Cohort Study

Background/Aim: Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are ubiquitous and persistent environmental chemicals and are suggested to have immunosuppressive effects. Studies indicate that prenatal exposure to PFAS may lead to suppressed immune responses in early life. However, human studies of immune effects are inconsistent. In this study, we aim to assess the association between prenatal exposure of PFASs with isomers and serum antibody concentrations against measles, coxsackievirus A 16 (CA16) and enterovirus 71 (EV71) toxoids in newborn and infant at 3 months. Methods: We recruited 295 pairs of mothers and their infants in Guangzhou Birth Cohort Study, China from July to October 2013. Measles IgG antibody was examined using ELISA assay, neutralizing antibodies titers against CA16, EV71 toxoids were performed in cord blood serum and infant aged 3 months, respectively. A PFAS isomer-specific analysis method based on high performance liquid chromatography-mass spectrometry (HPLC-MS/MS) was applied to determine the PFASs and isomers concentration in cord blood serum. Results: For measles antibody, PFOA showed the strongest negative correlations with toxoid antibody concentration in newborn and 3-month infant. A doubling of lnPFOA level (ng/ml) increasing among newborn and 3-m infant was associated with a difference of -24.4% (95% CI: -30.7, -17.5) and -33.3% (95% CI: --43.9, -20.6) in measles antibody concentration, respectively. A doubling ln-unit (ng/ml) increase in total branch PFOS isomers in 3-month infant was associated with higher odds ratio of 1.70 (95%: 1.03, 2.79) and 2.49 (95%, 1.45, 4.28) than that with linear PFOS for falling below a clinically protection level (<1_8 titers) for CA16 and EV71 antibody, respectively. This association was more obvious in boys than in girls. Interestingly, we observed that long-chain PFASs, such as perflouorotetradodecanoic acid (PFDoDA) and perfluoroundecanoic acid (PFUnDA) exposure were negatively associated with measles, CA16 and EV71 antibody level in both newborn and 3-month infant. Conclusions: Elevated prenatal exposures to PFASs, including long-chain PFASs were associated with depressed toxoid antibody response in newborn and infant. Branch isomer shows higher impact on CA16 and EV71 antibody level in 3-month infant for bellowing clinical protection.

IFN-γ Influences Epithelial Antiviral Responses via Histone Methylation of the RIG-I Promoter.

The asthmatic lung is prone to respiratory viral infections that exacerbate the symptoms of the underlying disease. Recent work has suggested that a deficient T-helper cell type 1 response in early life may lead to these aberrant antiviral responses. To study the development of long-term dysregulation of innate responses, which is a hallmark of asthma, we investigated whether the inflammatory environment of the airway epithelium can modulate antiviral gene expression via epigenetic mechanisms. We primed AALEB cells, a human bronchial epithelial cell line, with IFN-γ and IL-13, and subsequently infected the cells with respiratory syncytial virus (RSV). We then analyzed the expression of innate antiviral genes and their epigenetic markers. Priming epithelial cells with IFN-γ reduced the RSV viral load. Microarray analysis identified that IFN-γ priming enhanced retinoic acid-inducible gene (RIG)-I mRNA expression, and this expression correlated with epigenetic changes at the RIG-I promoter that influenced its transcription. Using chromatin immunoprecipitation, we observed a reduction of trimethylated histone 3 lysine 9 at the RIG-I promoter. Addition of inhibitor BIX-01294 to this model indicated an involvement of lysine methyltransferase G9a in RIG-I epigenetic regulation. These data suggest that prior exposure to IFN-γ may leave an epigenetic mark on the chromatin that enhances airway cells' ability to resist infection, possibly via epigenetic upregulation of RIG-I. These observations provide further evidence for a crucial role of IFN-γ in the development of mature antiviral responses within a model of respiratory infection. Further clinical validation is required to determine whether this effect in early life leads to changes in antiviral responses associated with asthma.

Tissue compartmentalization of T cell responses during early life.

The immune system in early life is tasked with transitioning from a relatively protected environment to one in which it encounters a wide variety of innocuous antigens and dangerous pathogens. The immaturity of the developing immune system, and particularly the distinct functionality of T lymphocytes in early life, has been implicated in increased susceptibility to infection. Previous work has demonstrated that immune responses in early life are skewed toward limited inflammation and atopy; however, there is mounting evidence that such responses are context- and tissue-dependent. The regulation, differentiation, and maintenance of infant T cell responses, particularly as it relates to tissue compartmentalization, remains poorly understood. How the tissue environment impacts early-life immune responses and whether the development of localized protective immune memory cell subsets are established is an emerging area of research. As infectious diseases affecting the respiratory and digestive tracts are a leading cause of morbidity and mortality worldwide in infants and young children, a deeper understanding of site-specific immunity is essential to addressing these challenges. Here, we review the current paradigms of T cell responses during infancy as they relate to tissue localization and discuss implications for the development of vaccines and therapeutics.

Negative Correlation between Circulating CD4+FOXP3+CD127- Regulatory T Cells and Subsequent Antibody Responses to Infant Measles Vaccine but Not Diphtheria-Tetanus-Pertussis Vaccine Implies a Regulatory Role.

Regulatory T cells (Tregs) play a key homeostatic role by suppressing immune responses. They have been targeted in mouse and human cancer studies to improve vaccine immunogenicity and tumor clearance. A number of commercially available drugs and experimental vaccine adjuvants have been shown to target Tregs. Infants have high numbers of Tregs and often have poor responses to vaccination, yet the role Tregs play in controlling vaccine immunogenicity has not been explored in this age group. Herein, we explore the role of CD4+FOXP3+CD127− Tregs in controlling immunity in infant males and females to vaccination with diphtheria–tetanus–whole cell pertussis (DTP) and/or measles vaccine (MV). We find correlative evidence that circulating Tregs at the time of vaccination suppress antibody responses to MV but not DTP; and Tregs 4 weeks after DTP vaccination may suppress vaccine-specific cellular immunity. This opens the exciting possibility that Tregs may provide a future target for improved vaccine responses in early life, including reducing the number of doses of vaccine required. Such an approach would need to be safe and the benefits outweigh the risks, thus further research in this area is required.

Age-dependent plasticity in endocannabinoid modulation of pain processing through postnatal development.

Significant age- and experience-dependent remodelling of spinal and supraspinal neural networks occur, resulting in altered pain responses in early life. In adults, endogenous opioid peptide and endocannabinoid (ECs) pain control systems exist which modify pain responses, but the role they play in acute responses to pain and postnatal neurodevelopment is unknown. Here, we have studied the changing role of the ECs in the brainstem nuclei essential for the control of nociception from birth to adulthood in both rats and humans. Using in vivo electrophysiology, we show that substantial functional changes occur in the effect of microinjection of ECs receptor agonists and antagonists in the periaqueductal grey (PAG) and rostroventral medulla (RVM), both of which play central roles in the supraspinal control of pain and the maintenance of chronic pain states in adulthood. We show that in immature PAG and RVM, the orphan receptor, GPR55, is able to mediate profound analgesia which is absent in adults. We show that tissue levels of endocannabinoid neurotransmitters, anandamide and 2-arachidonoylglycerol, within the PAG and RVM are developmentally regulated (using mass spectrometry). The expression patterns and levels of ECs enzymes and receptors were assessed using quantitative PCR and immunohistochemistry. In human brainstem, we show age-related alterations in the expression of key enzymes and receptors involved in ECs function using PCR and in situ hybridisation. These data reveal that significant changes on ECs that to this point have been unknown and which shed new light into the complex neurochemical changes that permit normal, mature responses to pain.

Patterns of immune development in urban preschoolers with recurrent wheeze and/or atopy

Disadvantaged urban children have high rates of allergic diseases and wheezing, which are diseases associated with type 2-biased immunity. We sought to determine whether environmental exposures in early life influence cytokine responses that affect the development of recurrent wheezing illnesses and allergic sensitization. A birth cohort of 560 urban families was recruited from neighborhoods with high rates of poverty, and 467 (83%) children were followed until 3years of age. Cytokine responses were measured in blood cell samples obtained at birth (cord blood) and ages 1 and 3years. Cytokine responses were examined in relation to personal characteristics and environmental exposures to allergens and endotoxin and to the development of allergic sensitization and recurrent wheeze assessed at age 3years. Cytokine responses generally increased with age, but responses at birth were poorly predictive for those at ages 1 and 3years. Exposure to certain allergens (cockroach, mouse, dust mite) was significantly associated with enhanced cytokine responses at age 3years, including IFN-α and IL-10 responses to certain stimulants and responses to phytohemagglutinin. Regarding the clinical outcomes, reduced LPS-induced IL-10 responses at birth were associated with recurrent wheeze. In contrast, reduced respiratory syncytial virus-induced IL-8 responses and increased 5'-cytosine-phosphate-guanine-3' (CpG)-induced IL-12p40 and allergen-induced IL-4 responses were associated with atopy. These findings suggest that diverse biologic exposures, including allergens and endotoxin, in urban homes stimulate the development of cytokine responses in early life, and that cytokine responses to specific microbial and viral stimuli are associated with the development of allergic sensitization and recurrent wheeze.

Maternal IgG and IgA Antibodies Dampen Mucosal T Helper Cell Responses in Early Life

To maintain a symbiotic relationship between the host and its resident intestinal microbiota, appropriate mucosal Tcell responses to commensal antigens must be established. Mice acquire both IgG and IgA maternally; the former has primarily been implicated in passive immunity to pathogens while the latter mediates host-commensal mutualism. Here, we report the surprising observation that mice generate Tcell-independent and largely Toll-like receptor (TLR)-dependent IgG2b and IgG3 antibody responses against their gut microbiota. We demonstrate that maternal acquisition of these antibodies dampens mucosal T follicular helper responses and subsequent germinal center B cell responses following birth. This work reveals a feedback loop whereby Tcell-independent, TLR-dependent antibodies limit mucosal adaptive immune responses to newly acquired commensal antigens and uncovers a broader function for maternal IgG.

Circulating Human Neonatal Naïve B Cells are Deficient in CD73 Impairing Purine Salvage.

Extracellular purines, in particular adenosine (Ado) and adenosine-triphosphate, are critical immunoregulatory molecules. Expression and activity of purine ecto-enzymes on B cells in neonatal and adult blood may influence their function and has been incompletely characterized. Mononuclear cells were isolated from human neonatal (cord blood) or adult (peripheral blood) subjects and evaluated directly by flow cytometry for expression of purine ecto-enzymes. Additionally, B cell subsets were isolated from mononuclear cell fractions by fluorescence-activated cell sorting and gene transcription of purine ecto-enzymes (CD39 and CD73), Ado deaminase (ADA1), purine nucleoside phosphorylase, and select purine receptors (A2a) were evaluated by reverse transcription followed by qRT-PCR. Immuno-magnetic-bead isolated naïve B cells were evaluated for enzymatic activity by incubation with radio-labeled purines followed by thin-layer chromatography, and subsequent B cell Ado acquisition was evaluated by liquid scintillation quantitation of radio-labeled Ado uptake. Relative to their adult counterparts, neonatal circulating naïve B cells were markedly and selectively deficient in CD73 as observed by gene transcription, surface protein expression, and enzyme activity. Neonatal naïve B cell deficiency of CD73 expression significantly impaired their capacity to acquire extracellular purines for purine salvage. Human neonatal circulating naïve B cells are selectively deficient in CD73, impairing extracellular purine acquisition and potentially contributing to impaired B cell responses in early life.

Early-life compartmentalization of human T cell differentiation and regulatory function in mucosal and lymphoid tissues.

It is unclear how the immune response in early life becomes appropriately stimulated to provide protection while also avoiding excessive activation as a result of diverse new antigens. T cells are integral to adaptive immunity; mouse studies indicate that tissue localization of T cell subsets is important for both protective immunity and immunoregulation. In humans, however, the early development and function of T cells in tissues remain unexplored. We present here an analysis of lymphoid and mucosal tissue T cells derived from pediatric organ donors in the first two years of life, as compared to adult organ donors, revealing early compartmentalization of T cell differentiation and regulation. Whereas adult tissues contain a predominance of memory T cells, in pediatric blood and tissues the main subset consists of naive recent thymic emigrants, with effector memory T cells (T(EM)) found only in the lungs and small intestine. Additionally, regulatory T (T(reg)) cells comprise a high proportion (30-40%) of CD4(+) T cells in pediatric tissues but are present at much lower frequencies (1-10%) in adult tissues. Pediatric tissue T(reg) cells suppress endogenous T cell activation, and early T cell functionality is confined to the mucosal sites that have the lowest T(reg):T(EM) cell ratios, which suggests control in situ of immune responses in early life.

Factors influencing innate immunity and vaccine responses in infancy.

Despite significant progress in reducing the burden of mortality in children under the age of five, reducing mortality in newborns remains a major challenge. Infection plays a significant role in infant deaths and interventions such as early vaccination or antenatal immunization could make a significant contribution to prevention of such deaths. In the last few years, we have gained new insights into immune ontogeny and are now beginning to understand the impact of vaccines, nutrition and environmental factors on 'training' of the immune response in early life. This review article sets out to explain why vaccine responses can be heterogeneous between populations and individuals by providing examples chosen to illustrate the impact of host, pathogen and environmental factors on shaping the immune 'interactome' in young children.

The genetic regulation of infant immune responses to vaccination.

A number of factors are recognized to influence immune responses to vaccinations including age, gender, the dose, and quality of the antigen used, the number of doses given, the route of administration, and the nutritional status of the recipient. Additionally, several immunogenetic studies have identified associations between polymorphisms in genes encoding immune response proteins, both innate and adaptive, and variation in responses to vaccines. Variants in the genes encoding Toll-like receptors, HLA molecules, cytokines, and cytokine receptors have associated with heterogeneity of responses to a wide range of vaccines including measles, hepatitis B, influenza A, BCG, Haemophilus influenzae type b, and certain Neisseria meningitidis serotypes, amongst others. However, the vast majority of these studies have been conducted in older children and adults and there are very few data available from studies conducted in infants. This paper reviews the evidence to date that host genes influencing vaccines responses in these older population and identifies a large gap in our understanding of the genetic regulation of responses in early life. Given the high mortality from infection in early life and the challenges of developing vaccines that generate effective immune responses in the context of the developing immune system further research on infant populations is required.

Gut microbiota: a source of novel tools to reduce the risk of human disease?

Modern civilization is faced with a progressive increase in immune-mediated or inflammatory health problems such as allergic disease, autoimmune disorders, and obesity. An extended version of the hygiene hypothesis has been introduced to emphasize the intimate interrelationship among diet, the immune system, microbiome, and origins of human disease: the modern infant, particularly when delivered by cesarean section and without the recommended exclusive breastfeeding, may lack sufficient stimulation of the mucosal immune system to generate a tolerogenic immune milieu and instead be prone to develop chronic inflammatory conditions. These deviations may take the form of allergic or autoimmune disease, or predispose the child to higher weight gain and obesity. Moreover, evidence supports the role of first microbial contacts in promoting and maintaining a balanced immune response in early life and recent findings suggest that microbial contact begins prior to birth and is shaped by the maternal microbiota. Maternal microbiota may prove to be a safe and effective target for interventions decreasing the risk of allergic and noncommunicable diseases in future generations. These results support the hypothesis that targeting early interaction with microbes might offer an applicable strategy to prevent disease.

IS-010 Cell-based Immunity Of The Newborn

<h3></h3> Irrespective of host genetic factors, newborns and infants are characterised by a higher susceptibility to particular infections. Thus, these populations constitute privileged targets and reservoirs for existing and emerging diseases. They carry influenza virus, respiratory syncytial virus or <i>B. pertussis</i> leading to severe respiratory diseases in these fragile populations. Vaccination represents a powerful mean to provide protection against many infectious diseases, but with limited efficacy in the first few months of life. One main reason is that vaccine design does not take into account age-specific immune parameters of the populations receiving immunizations, i.e. neonates and infants. Systems biology has initiated the definition of a comprehensive picture to accurately define protection correlates. However age-specific immune parameters are still missing for appropriate signal deconvolution in high throughput immune system analyses. The gaps in the knowledge of the immune system of the newborn and the infant need to be filled to propose appropriate prophylactic and therapeutic treatments to these vulnerable populations. We established a Human-Mouse experimental platform to study pathogen-neonatal immune host interactions and to design and evaluate age-specific vaccine strategies. Apart from the traditional view of immaturity, we recently evidenced immunological unfitness related to age-specific effector and regulatory mechanisms tuning immune responses in early life. We thus evidenced development of memory T cells and innate antibody responses during fetal life. We also characterised new innate inflammatory pathways in dendritic cells for future adjuvant setting in paediatric vaccination.

The role of environmental factors in modulating immune responses in early life.

The concept of immunological memory stipulates that past exposures shape present immune function. These exposures include not only specific antigens impacting adaptive immune memory but also conserved pathogen or danger associated molecular patterns that mold innate immune responses for prolonged periods of time. It should thus not come as a surprise that there is a vast range of external or environmental factors that impact immunity. The importance of environmental factors modulating immunity is most readily recognized in early life, a period of rapidly changing environments. We here summarize available data on the role of environment shaping immune development and from it derive an overarching hypothesis relating the underlying molecular mechanisms and evolutionary principles involved.

The effect of stable macromolecular complexes of ionic polyphosphazene on HIV Gag antigen and on activation of human dendritic cells and presentation to T-cells

Neonates and infants are susceptible to infection due to distinct immune responses in early life. Therefore, development of vaccine formulation and delivery systems capable of activating human newborn leukocytes is of global health importance. Poly[di(carboxylatophenoxy)phosphazene] (PCPP) belongs to a family of ionic synthetic polyphosphazene polyelectrolyte compounds that can form non-covalent interactions with protein antigens and demonstrate adjuvant activity in animals and in human clinical trials. However, little is known about their ability to activate human immune cells. In this study, we characterized the effects of PCPP alone or in combination with a model antigen (recombinant HIV-Gag (Gag)), on the maturation, activation and antigen presentation by human adult and newborn dendritic cells (DCs) in vitro. PCPP treatment induced DC activation as assessed by upregulation of co-stimulatory molecules and cytokine production. Studies benchmarking PCPP to Alum, the most commonly used vaccine adjuvant, demonstrated that both triggered cell death and release of danger signals in adult and newborn DCs. When complexed with Gag antigen, PCPP maintained its immunostimulatory characteristics while permitting internalization and presentation of Gag by DCs to HIV-Gag-specific CD4+ T cell clones. The PCPP vaccine formulation outlined here has intrinsic adjuvant activity, can facilitate effective delivery of antigen to DCs, and may be advantageous for induction of beneficial T cell-mediated immunity. Moreover, polyphosphazenes can further reduce cost of vaccine production and distribution through their dose-sparing and antigen-stabilizing properties, thus potentially eliminating the need for cold chain distribution.

IL-4 and IL-13 differentially regulate TLR-induced eosinophil-basophil differentiation of cord blood CD34+ progenitor cells.

Intrauterine environmental exposures have been shown to influence neonatal immunity and subsequent allergic disease development. We have previously shown that fewer lipopolysaccharide (LPS)-stimulated eosinophil-basophil (Eo/B) colonies grow from cord blood (CB) of high-atopic risk infants, compared to low-atopic risk infants. In the present study, we investigated whether a surrogate ex vivo TH2 milieu (i.e., either IL-4 or IL-13) could represent an underlying mechanism to explain our previous findings. CB CD34+ cells from healthy donors were cultured with IL-4 or IL-13 (in combination with LPS) and assessed for Eo/B differentiation using methylcellulose cultures and flow cytometry for related intracellular signalling pathways. Pharmacological inhibitors were added to the methylcellulose cultures to determine the effect of blocking intracellular signalling in CB CD34+ cells in relation to Eo/B colony forming unit (CFU) formation. Stimulation of CD34+ cells with IL-4, but not IL-13, reduced Eo/B CFU formation in the presence of LPS; this was found to be dependent on IL-4Rα and not IL-13Rα1. Additionally, IL-4 reduced the expression of ERK 1/2 after LPS stimulation, which was recovered by inhibition of IL-4Rα. While IL-13 did not have an inhibitory effect on ERK 1/2 expression, inhibition of ERK 1/2 significantly reduced Eo/B CFU formation. Thus, the responsiveness of CB CD34+ progenitor cells to LPS is differentially regulated by the TH2 cytokines, IL-4 and IL-13. This may have implications for in utero interactions between placental-derived pro-allergic cytokines and neonatal progenitor cells influencing Eo/B-mediated inflammatory responses in early life.

An alphavirus-based adjuvant enhances serum and mucosal antibodies, T cells, and protective immunity to influenza virus in neonatal mice.

Neonatal immune responses to infection and vaccination are biased toward TH2 at the cost of proinflammatory TH1 responses needed to combat intracellular pathogens. However, upon appropriate stimulation, the neonatal immune system can induce adult-like TH1 responses. Here we report that a new class of vaccine adjuvant is especially well suited to enhance early life immunity. The GVI3000 adjuvant is a safe, nonpropagating, truncated derivative of Venezuelan equine encephalitis virus that targets dendritic cells (DCs) in the draining lymph node (DLN) and produces intracellular viral RNA without propagating to other cells. RNA synthesis strongly activates the innate immune response so that in adult animals, codelivery of soluble protein antigens induces robust humoral, cellular, and mucosal responses. The adjuvant properties of GVI3000 were tested in a neonatal BALB/c mouse model using inactivated influenza virus (iFlu). After a single immunization, mice immunized with iFlu with the GVI3000 adjuvant (GVI3000-adjuvanted iFlu) had significantly higher and sustained influenza virus-specific IgG antibodies, mainly IgG2a (TH1), compared to the mice immunized with antigen only. GVI3000 significantly increased antigen-specific CD4(+) and CD8(+) T cells, primed mucosal immune responses, and enhanced protection from lethal challenge. As seen in adult mice, the GVI3000 adjuvant increased the DC population in the DLNs, caused activation and maturation of DCs, and induced proinflammatory cytokines and chemokines in the DLNs soon after immunization, including gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), granulocyte colony-stimulating factor (G-CSF), and interleukin 6 (IL-6). In summary, the GVI3000 adjuvant induced an adult-like adjuvant effect with an influenza vaccine and has the potential to improve the immunogenicity and protective efficacy of new and existing neonatal vaccines. The suboptimal immune responses in early life constitute a significant challenge for vaccine design. Here we report that a new class of adjuvant is safe and effective for early life immunization and demonstrate its ability to significantly improve the protective efficacy of an inactivated influenza virus vaccine in a neonatal mouse model. The GVI3000 adjuvant delivers a truncated, self-replicating viral RNA into dendritic cells in the draining lymph node. Intracellular RNA replication activates a strong innate immune response that significantly enhances adaptive antibody and cellular immune responses to codelivered antigens. A significant increase in protection results from a single immunization. Importantly, this adjuvant also primed a mucosal IgA response, which is likely to be critical for protection during many early life infections.