The murine Th2 locus undergoes epigenetic modification in the thymus during fetal and postnatal ontogeny

Multiple waves of fetal-derived immune cells constitute adult immune system

It has been over three decades since Drs. Herzenberg and Herzenberg proposed the layered immune system hypothesis, suggesting that different types of stem cells with distinct hematopoietic potential produce specific immune cells. This layering of immune system development is now supported by recent studies showing the presence of fetal-derived immune cells that function in adults. It has been shown that various immune cells arise at different embryonic ages via multiple waves of hematopoiesis from special endothelial cells (ECs), referred to as hemogenic ECs. However, it remains unknown whether these fetal-derived immune cells are produced by hematopoietic stem cells (HSCs) during the fetal to neonatal period. To address this question, many advanced tools have been used, including lineage-tracing mouse models, cellular barcoding techniques, clonal assays, and transplantation assays at the single-cell level. In this review, we will review the history of the search for the origins of HSCs, B-1a progenitors, and mast cells in the mouse embryo. HSCs can produce both B-1a and mast cells within a very limited time window, and this ability declines after embryonic day (E) 14.5. Furthermore, the latest data have revealed that HSC-independent adaptive immune cells exist in adult mice, which implies more complicated developmental pathways of immune cells. We propose revised road maps of immune cell development.

Neonatal Immune Responses to Respiratory Viruses

Respiratory tract infections are a leading cause of morbidity and mortality in newborns, infants, and young children. These early life infections present a formidable immunologic challenge with a number of possibly conflicting goals: simultaneously eliminate the acute pathogen, preserve the primary gas-exchange function of the lung parenchyma in a developing lung, and limit long-term sequelae of both the infection and the inflammatory response. The latter has been most well studied in the context of childhood asthma, where multiple epidemiologic studies have linked early life viral infection with subsequent bronchospasm. This review will focus on the clinical relevance of respiratory syncytial virus (RSV), human metapneumovirus (HMPV), and rhinovirus (RV) and examine the protective and pathogenic host responses within the neonate.

Epigenetic regulation of pediatric and neonatal immune responses

Epigenetic regulation of transcription is a collective term that refers to mechanisms known to regulate gene transcription without changing the underlying DNA sequence. These mechanisms include DNA methylation and histone tail modifications which influence chromatin accessibility, and microRNAs that act through post-transcriptional gene silencing. Epigenetics is known to regulate a variety of biological processes, and the role of epigtenetics in immunity and immune-mediated diseases is becoming increasingly recognized. While DNA methylation is the most widely studied, each of these systems play an important role in the development and maintenance of appropriate immune responses. There is clear evidence that epigenetic mechanisms contribute to developmental stage-specific immune responses in a cell-specific manner. There is also mounting evidence that prenatal exposures alter epigenetic profiles and subsequent immune function in exposed offspring. Early life exposures that are associated with poor long-term health outcomes also appear to impact immune specific epigenetic patterning. Finally, each of these epigenetic mechanisms contribute to the pathogenesis of a wide variety of diseases that manifest during childhood. This review will discuss each of these areas in detail. IMPACT: Epigenetics, including DNA methylation, histone tail modifications, and microRNA expression, dictate immune cell phenotypes. Epigenetics influence immune development and subsequent immune health. Prenatal, perinatal, and postnatal exposures alter immune cell epigenetic profiles and subsequent immune function. Numerous pediatric-onset diseases have an epigenetic component. Several successful strategies for childhood diseases target epigenetic mechanisms.

Human CD36hi monocytes induce Foxp3+ CD25+ T cells with regulatory functions from CD4 and CD8 subsets

The fetal and neonatal immune systems are uniquely poised to generate tolerance to self, maternal and environmental antigens encountered in the womb and shortly after birth. However, the tolerogenic nature of fetal and neonatal immunity can be detrimental in the context of pathogens, leading to overwhelming bacterial infections or chronic viral infections. A variety of mechanisms contribute to fetal and neonatal tolerance, including a propensity to generate Foxp3⁺ regulatory T cells (Treg cells). However, the mechanism(s) of fetal Foxp3⁺ T-cell differentiation, the specific antigen-presenting cells required and factors that inhibit Treg generation after the neonatal period are poorly understood. Here, we demonstrate that a subset of CD14⁺ monocytes expressing the scavenger molecule, CD36, can generate CD4⁺ and CD8⁺ T cells that coexpress Foxp3 and T-bet from both umbilical cord blood. These Foxp3⁺ T-bet⁺ T cells potently suppress T-cell proliferation and ameliorate xenogeneic graft-versus-host disease. CD14⁺  CD36⁺ monocytes provide known Treg-inducing signals: membrane-bound transforming growth factor-beta and retinoic acid. Unexpectedly, adult peripheral blood monocytes are also capable of inducing Foxp3⁺ T cells from both cord blood and adult peripheral naïve T cells. The induction of Foxp3⁺ T cells in umbilical cord blood by monocytes was inhibited by the lymphoid fraction of adult peripheral blood cells. These studies highlight a novel immunoregulatory role of monocytes and suggest that antigen presentation by CD36^hi monocytes may contribute to the peripheral development of Foxp3⁺ T-bet⁺ T cells with regulatory functions in both neonates and adults.

Preventing Atopic Diseases During Childhood - Early Exposure Matters

Atopic diseases in childhood are a major burden worldwide and there is still a lack of knowledge about treatable causes. In industrialized countries such as Germany, almost every second child is sensitized to at least one common allergen. Recent studies show that although the predisposition to allergies is inherited, the adaptive immune system of neonates and infants follows a developmental trajectory and whether an allergy actually occurs depends also on timing of allergen exposure including diet as well as environmental factors. New recommendations are far from being rigid of allergen avoidance; it is rather moving toward conditions that stand for more biodiversity. The observation that introduction of peanuts or eggs early in life significantly reduced the development of a later allergy will change our recommendations for the introduction of complementary foods. This is consistent with the hygiene hypothesis that early provocation shapes the developing immune system so that it reacts appropriately. Therefore, promoting the development of tolerance is at the heart of sensible allergy prevention - and this begins with the last trimester of pregnancy. In light of this concept, actual recommendations are discussed.

Modulating local airway immune responses to treat allergic asthma: lessons from experimental models and human studies

With asthma affecting over 300 million individuals world-wide and estimated to affect 400 million by 2025, developing effective, long-lasting therapeutics is essential. Allergic asthma, where Th2-type immunity plays a central role, represents 90% of child and 50% of adult asthma cases. Research based largely on animal models of allergic disease have led to the generation of a novel class of drugs, so-called biologicals, that target essential components of Th2-type inflammation. Although highly efficient in subclasses of patients, these biologicals and other existing medication only target the symptomatic stage of asthma and when therapy is ceased, a flare-up of the disease is often observed. Therefore, it is suggested to target earlier stages in the inflammatory cascade underlying allergic airway inflammation and to focus on changing and redirecting the initiation of type 2 inflammatory responses against allergens and certain viral agents. This focus on upstream aspects of innate immunity that drive development of Th2-type immunity is expected to have longer-lasting and disease-modifying effects, and may potentially lead to a cure for asthma. This review highlights the current understanding of the contribution of local innate immune elements in the development and maintenance of inflammatory airway responses and discusses available leads for successful targeting of those pathways for future therapeutics.

Evaluation of the Induction of Cell-Mediated Immunity Against Candida albicans in a Model of Cutaneous Infection in Newborn 0-Day-Old Mice

Candida albicans is a commensal fungus of the skin and mucous membranes in humans, but it is also responsible for mucocutaneous and systemic infections in immunocompromised patients like low birth weight neonates and premature newborns. The epicutaneous application of C. albicans is widely used to study the immune response against this pathogen in adult mice models. However, the immune response of newborns against infections caused by the genus Candida is poorly understood. In order to mimic premature human infection, we developed a model of C. albicans epicutaneous infection in newborn mice. We found that yeasts were able to colonize while the pseudohyphae invaded the epidermis. Recruitment of polymorphonuclear and mononuclear cells at the infection zone was observed. Fungal invasion, fungal burden and cellular infiltration displayed a time- and dose-dependent response. Interestingly, newborn mice were able to control C. albicans primary infection. Finally, we showed that the epicutaneous infection of C. albicans in newborn mice at birth results in the induction of cell-mediated immunity as evinced by delayed-type hypersensitivity assays.

Epigenetic mechanisms regulating T-cell responses

During the last decade, advances in sequencing technologies allowed production of a wealth of information on epigenetic modifications in T cells. Epigenome maps, in combination with mechanistic studies, have demonstrated that T cells undergo extensive epigenome remodeling in response to signals, which has a strong effect on phenotypic stability and function of lymphocytes. In this review we focus on DNA methylation, histone modifications, and chromatin structure as important epigenetic mechanisms involved in controlling T-cell responses. In particular, we discuss epigenetic processes in light of the development, activation, and differentiation of CD4⁺ T helper (T_H), regulatory T, and CD8⁺ T cells. As central aspects of the adaptive immune system, we review mechanisms that ensure molecular memory, stability, plasticity, and exhaustion of T cells. We further discuss the effect of the tissue environment on imprinting T-cell epigenomes with potential implications for immunotherapy.

Polyphenol Effects on Splenic Cytokine Response in Post-Weaning Contactin 1-Overexpressing Transgenic Mice

Background: In mice, postnatal immune development has previously been investigated, and evidence of a delayed maturation of the adaptive immune response has been detected. Methods: In this study, the effects of red grape polyphenol oral administration on the murine immune response were explored using pregnant mice (TAG/F3 transgenic and wild type (wt) mice) as the animal model. The study was performed during pregnancy as well as during lactation until postnatal day 8. Suckling pups from polyphenol-administered dams as well as day 30 post-weaning pups (dietary-administered with polyphenols) were used. Polyphenol effects were evaluated, measuring splenic cytokine secretion. Results: Phorbol myristate acetate-activated splenocytes underwent the highest cytokine production at day 30 in both wt and TAG/F3 mice. In the latter, release of interferon (IFN)-γ and tumor necrosis factor (TNF)-α was found to be higher than in the wt counterpart. In this context, polyphenols exerted modulating activities on day 30 TAG/F3 mice, inducing release of interleukin (IL)-10 in hetero mice while abrogating release of IL-2, IFN-γ, TNF-α, IL-6, and IL-4 in homo and hetero mice. Conclusion: Polyphenols are able to prevent the development of an inflammatory/allergic profile in postnatal TAG/F3 mice.

Human Naive T Cells Express Functional CXCL8 and Promote Tumorigenesis

Naive T cells are thought to be functionally quiescent. In this study, we studied and compared the phenotype, cytokine profile, and potential function of human naive CD4+ T cells in umbilical cord and peripheral blood. We found that naive CD4+ T cells, but not memory T cells, expressed high levels of chemokine CXCL8. CXCL8+ naive T cells were preferentially enriched CD31+ T cells and did not express T cell activation markers or typical Th effector cytokines, including IFN-γ, IL-4, IL-17, and IL-22. In addition, upon activation, naive T cells retained high levels of CXCL8 expression. Furthermore, we showed that naive T cell-derived CXCL8 mediated neutrophil migration in the in vitro migration assay, supported tumor sphere formation, and promoted tumor growth in an in vivo human xenograft model. Thus, human naive T cells are phenotypically and functionally heterogeneous and can carry out active functions in immune responses.

Neonatal Immunity, Respiratory Virus Infections, and the Development of Asthma

Infants are exposed to a wide range of potential pathogens in the first months of life. Although maternal antibodies acquired transplacentally protect full-term neonates from many systemic pathogens, infections at mucosal surfaces still occur with great frequency, causing significant morbidity and mortality. At least part of this elevated risk is attributable to the neonatal immune system that tends to favor T regulatory and Th2 type responses when microbes are first encountered. Early-life infection with respiratory viruses is of particular interest because such exposures can disrupt normal lung development and increase the risk of chronic respiratory conditions, such as asthma. The immunologic mechanisms that underlie neonatal host-virus interactions that contribute to the subsequent development of asthma have not yet been fully defined. The goals of this review are (1) to outline the differences between the neonatal and adult immune systems and (2) to present murine and human data that support the hypothesis that early-life interactions between the immune system and respiratory viruses can create a lung environment conducive to the development of asthma.

Dectin-1 activation unlocks IL12A expression and reveals the TH1 potency of neonatal dendritic cells

BACKGROUND

Early life is characterized by a high susceptibility to infection and a TH2-biased CD4 T-cell response to vaccines. Toll-like receptor (TLR) agonists are currently being implemented as new vaccine adjuvants for TH1 activation, but their translation to the field of pediatric vaccines is facing the impairment of neonatal innate TLR responses.

OBJECTIVE

We sought to analyze C-type lectin receptor pathways as an alternative or a coactivator to TLRs for neonatal dendritic cell activation for TH1 polarization.

METHODS

Neonatal monocyte-derived dendritic cells (moDCs) were exposed to various combinations of TLR agonists with or without Dectin-1 agonist. IL-12 and IL-23 responses were analyzed at the transcriptional and protein levels after stimulation. The intracellular pathways triggered by combined TLR plus Dectin-1 stimulation was determined by using pharmacologic inhibitors. The capacity of neonatal moDCs to differentiate naive CD4 TH cells was evaluated in cocultures with heterologous neonatal naive T cells. Curdlan was finally tested as an adjuvant within a subunit tuberculosis vaccine in neonatal mice.

RESULTS

Simultaneous coactivation through Dectin-1 and TLRs induced robust secretion of IL-12p70 by neonatal moDCs by unlocking transcriptional control on the p35 subunit of IL-12. Both the spleen tyrosine kinase and Raf-1 pathways were involved in this process, allowing differentiation of neonatal naive T cells toward IFN-γ-producing TH1 cells. In vivo a Dectin-1 agonist as adjuvant was sufficient to induce TH1 responses after vaccination of neonatal mice.

CONCLUSION

Coactivation of neonatal moDCs through Dectin-1 allows TLR-mediated IL-12p70 secretion and TH1 polarization of neonatal T cells. Dectin-1 agonists represent a promising TH1 adjuvant for pediatric vaccination.

CD4 T cells with effector memory phenotype and function develop in the sterile environment of the fetus

The T cell compartment is considered to be naïve and dedicated to the development of tolerance during fetal development. We have identified and characterized a population of fetally developed CD4 T cells with an effector memory phenotype (TEM), which are present in cord blood. This population is polyclonal and has phenotypic features similar to those of conventional adult memory T cells, such as CD45RO expression. These cells express low levels of CD25 but are distinct from regulatory T cells because they lack Foxp3 expression. After T cell receptor activation, neonatal TEM cells readily produced tumor necrosis factor-α (TNF-α) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We also detected interferon-γ (IFN-γ)-producing T helper 1 (TH1) cells and interleukin-4 (IL-4)/IL-13-producing TH2-like cells, but not IL-17-producing cells. We used chemokine receptor expression patterns to divide this TEM population into different subsets and identified distinct transcriptional programs using whole-genome microarray analysis. IFN-γ was found in CXCR3(+) TEM cells, whereas IL-4 was found in both CXCR3(+) TEM cells and CCR4(+) TEM cells. CCR6(+) TEM cells displayed a genetic signature that corresponded to TH17 cells but failed to produce IL-17A. However, the TH17 function of TEM cells was observed in the presence of IL-1β and IL-23. In summary, in the absence of reported pathology or any major infectious history, T cells with a memory-like phenotype develop in an environment thought to be sterile during fetal development and display a large variety of inflammatory effector functions associated with CD4 TH cells at birth.

Prenatal ethanol exposure induces an intrauterine programming of enhanced sensitivity of the hypothalamic–pituitary–adrenal axis in female offspring rats fed with post-weaning high-fat diet

“Intrauterine programming” involved in the intrauterine origin of prenatal ethanol exposure induced enhanced sensitivity of the HPA axis in female offspring rats fed with high-fat diet.

Immune responses in neonates

Neonates have little immunological memory and a developing immune system, which increases their vulnerability to infectious agents. Recent advances in the understanding of neonatal immunity indicate that both innate and adaptive responses are dependent on precursor frequency of lymphocytes, antigenic dose and mode of exposure. Studies in neonatal mouse models and human umbilical cord blood cells demonstrate the capability of neonatal immune cells to produce immune responses similar to adults in some aspects but not others. This review focuses mainly on the developmental and functional mechanisms of the human neonatal immune system. In particular, the mechanism of innate and adaptive immunity and the role of neutrophils, antigen presenting cells, differences in subclasses of T lymphocytes (Th1, Th2, Tregs) and B cells are discussed. In addition, we have included the recent developments in the neonatal mouse immune system. Understanding neonatal immunity is essential to development of therapeutic vaccines to combat newly emerging infectious agents.

Neonatal immunology: responses to pathogenic microorganisms and epigenetics reveal an "immunodiverse" developmental state

Neonatal animals have heightened susceptibility to infectious agents and are at increased risk for the development of allergic diseases, such as asthma. Experimental studies using animal models have been quite useful for beginning to identify the cellular and molecular mechanisms underlying these sensitivities. In particular, results from murine neonatal models indicate that developmental regulation of multiple immune cell types contributes to the typically poor responses of neonates to pathogenic microorganisms. Surprisingly, however, animal studies have also revealed that responses at mucosal surfaces in early life may be protective against primary or secondary disease. Our understanding of the molecular events underlying these processes is less well developed. Emerging evidence indicates that the functional properties of neonatal immune cells and the subsequent maturation of the immune system in ontogeny may be regulated by epigenetic phenomena. Here, we review recent findings from our group and others describing cellular responses to infection and developmentally regulated epigenetic processes in the newborn.