Cellular immune responses in neonates

Suppressive effect of therapeutic antibiotic regimen on antipneumococcal Th1/Th17 responses in neonatal mice

BACKGROUND

Antibiotics are commonly used in human neonates, but their impact on neonatal T cell immunity remains poorly understood. The aim of this study was to investigate the impact of the antibiotic piperacillin with the beta-lactamase inhibitor tazobactam on neonatal CD4+ and CD8+ T cell responses to Streptococcus pneumoniae.

METHODS

Splenic and lung cells were isolated from the neonatal mice receiving piperacillin and tazobactam or saline (sham) and cultured with S. pneumoniae to analyze T cell cytokine production by ELISA and flow cytometry.

RESULTS

Antibiotic exposure to neonatal mice resulted in reduced numbers of CD4+/CD8+ T cells in the spleen and lungs compared to control mice. Upon in vitro stimulation with S. pneumoniae, splenocytes and lung cells from antibiotic-exposed mice produced lower levels of IFN-γ (Th1)/IL-17A (Th17) and IL-17A cytokines, respectively. Flow cytometric analysis revealed that S. pneumoniae-stimulated splenic CD4+ T cells from antibiotic-exposed mice expressed decreased levels of IFN-γ and IL-17A compared to control mice, whereas lung CD4+ T cells produced lower levels of IL-17A. However, no significant difference was observed for IL-4 (Th2) production.

CONCLUSIONS

Neonatal mice exposure to piperacillin and tazobactam reduces the number of CD4+ and CD8+ T cells, and suppresses Th1 and Th17, but not Th2, responses to S. pneumoniae.

IMPACT

Exposure of neonatal mice with a combination of piperacillin and tazobactam reduces CD4+/CD8+ T cells in the spleen and lungs. Antibiotic exposure suppresses neonatal Th1 and Th17, but not Th2, responses to Streptococcus pneumoniae. Our findings may have important implications for developing better therapeutic strategies in the neonatal intensive care unit.

The changing landscape of immune cells in the fetal mouse testis

Fetal testis growth involves cell influx and extensive remodeling. Immediately after sex determination in mouse, macrophages enable normal cord formation and removal of inappropriately positioned cells. This study provides new information about macrophages and other immune cells after cord formation in fetal testes, including their density, distribution, and close cellular contacts. C57BL6J mouse testes from embryonic day (E) 13.5 to birth (post-natal day 0; PND0), were examined using immunofluorescence, immunohistochemistry, and RT-qPCR to identify macrophages (F4/80, CD206, MHCII), T cells (CD3), granulocytes/neutrophils (Ly6G), and germ cells (DDX4). F4/80⁺ cells were the most abundant, comprising 90% of CD45⁺ cells at E13.5 and declining to 65% at PND0. Changes in size, shape, and markers (CD206 and MHCII) documented during this interval align with the understanding that F4/80⁺ cells have different origins during embryonic life. CD3⁺ cells and F4/80⁻/MHCII⁺ were absent to rare until PND0. Ly6G⁺ cells were scarce at E13.5 but increased robustly by PND0 to represent half of the CD45⁺ cells. These immunofluorescence data were in accord with transcript analysis, which showed that immune marker mRNAs increased with testis age. F4/80⁺ and Ly6G⁺ cells were frequently inside cords adjacent to germ cells at E13.5 and E15.5. F4/80⁺ cells were often in clusters next to other immune cells. Macrophages inside cords at E13.5 and E15.5 (F4/80^Hi/CD206⁺) were different from macrophages at PND0 (F4/80^Dim/CD206⁻), indicating that they have distinct origins. This histological quantification coupled with transcript information identifies new cellular interactions for immune cells in fetal testis morphogenesis, and highlights new avenues for studies of their functional significance.

A M2 protein-based universal influenza vaccine containing Advax-SM adjuvant provides newborn protection via maternal or neonatal immunization

BACKGROUND

Despite newborns being at increased risk of serious influenza infection, influenza vaccines are currently not recommended for use in infants under 6 months of age. We therefore sought to evaluate the protective efficacy in mice of an M2-based influenza vaccine (CapM2e) formulated with Advax-SM adjuvant. Vaccine protection was assessed via both passive maternal immunization and direct neonatal immunization.

METHODS

For maternal transfer studies, female mice were immunized 1 week before and after mating. Blood was collected from both mother and offspring during weaning and pups were challenged when they reached 3 weeks of age with lethal doses of H1N1 and homologous reassortment influenza strain H3N2 with conserved M2. For direct immunization studies, newborns were immunized at 1 and 3 weeks of age and blood was collected prior to challenge at 4 weeks of age.

RESULTS

Maternal immunization with CapM2e + Advax-SM vaccine induced high maternal M2e antibody levels that were passively transferred to their offspring and provided them with protection against both H1N1 and H3N2 influenza strains when challenged at 3 weeks of age. When used for direct immunization of neonatal mice, CapM2e + Advax-SM vaccine similarly induced high serum M2e antibody levels and protected against H1N1 and H3N2 influenza challenges with protection associated with inhibition of virus replication with a significant reduction in lung virus load in immunized pups.

CONCLUSION

CapM2e + Advax-SM vaccine could be useful for protecting newborns against diverse influenza A strains, with opportunities to achieve protection by passive maternal immunization or active neonatal immunization. This data supports further development of this promising M2e-based vaccine candidate.

The Power of First Impressions: Can Influenza Imprinting during Infancy Inform Vaccine Design?

Influenza virus infection causes severe respiratory illness in people worldwide, disproportionately affecting infants. The immature respiratory tract coupled with the developing immune system, and lack of previous exposure to the virus is thought to synergistically play a role in the increased disease severity in younger age groups. No influenza vaccines are available for those under six months, although maternal influenza immunization is recommended. In children aged six months to two years, vaccine immunogenicity is dampened compared to older children and adults. Unlike older children and adults, the infant immune system has fewer antigen-presenting cells and soluble immune factors. Paradoxically, we know that a person's first infection with the influenza virus during infancy or childhood leads to the establishment of life-long immunity toward that particular virus strain. This is called influenza imprinting. We contend that by understanding the influenza imprinting event in the context of the infant immune system, we will be able to design more effective influenza vaccines for both infants and adults. Working through the lens of imprinting, using infant influenza animal models such as mice and ferrets which have proven useful for infant immunity studies, we will gain a better understanding of imprinting and its implications regarding vaccine design. This review examines literature regarding infant immune and respiratory development, current vaccine strategies, and highlights the importance of research into the imprinting event in infant animal models to develop more effective and protective vaccines for all including young children.

The liver as a nursery for leukocytes

Leukocytes are a large population of cells spread within most tissues in the body. These cells may be either sessile (called as resident cells) or circulating leukocytes, which travel long journeys inside the vessels during their lifespan. Although production and maturation of these leukocytes in adults primarily occur in the bone marrow, it is well known that this process-called hematopoiesis-started in the embryonic life in different sites, including the yolk sac, placenta, and the liver. In this review, we will discuss how the liver acts as a pivotal site for leukocyte maturation during the embryo phase, and also how the most frequent liver-resident immune cell populations-namely Kupffer cells, dendritic cells, and lymphocytes-play a vital role in both tolerance and inflammatory responses to antigens from food, microbiota, and pathogens.

Prebiotic oligosaccharides in early life alter gut microbiome development in male mice while supporting influenza vaccination responses

Beneficial modulation of the gut microbiota is an attractive therapeutic approach to improve the efficacy of vaccine-induced immunity. In this study, mice were supplemented with the prebiotic milk oligosaccharide 2'-fucosyllactose (2'FL) as well as a complex mixture of immune modulatory prebiotic short-chain galacto-oligosaccharides and long-chain fructo-oligosaccharides (scGOS/lcFOS) from different stages in early life. Adult mice were vaccinated with trivalent influenza vaccine (TIV) and both development of the gut microbiota and antibody-mediated vaccine responses were followed over time. Within the control group, female mice demonstrated a larger antibody response to TIV vaccination than male mice, which was accompanied by enhanced cytokine production by splenocytes and a higher percentage of plasma cells in skin draining lymph nodes. In addition, the prebiotic diet improved vaccine-specific antibody responses in male mice. Introduction of prebiotics into the diet modulated the gut microbiota composition and at the genus level several bacterial groups showed a significant interaction effect which potentially contributed to the immunological effects observed. This study provides insight in the effect of scGOS/lcFOS/2'FL in influenza vaccination antibody production.

Vaccine responses in newborns

Immunisation of the newborn represents a key global strategy in overcoming morbidity and mortality due to infection in early life. Potential limitations, however, include poor immunogenicity, safety concerns and the development of tolerogenicity or hypo-responsiveness to either the same antigen and/or concomitant antigens administered at birth or in the subsequent months. Furthermore, the neonatal immunological milieu is polarised towards Th2-type immunity with dampening of Th1-type responses and impaired humoral immunity, resulting in qualitatively and quantitatively poorer antibody responses compared to older infants. Innate immunity also shows functional deficiency in antigen-presenting cells: the expression and signalling of Toll-like receptors undergo maturational changes associated with distinct functional responses. Nevertheless, the effectiveness of BCG, hepatitis B and oral polio vaccines, the only immunisations currently in use in the neonatal period, is proof of concept that vaccines can be successfully administered to the newborn via different routes of delivery to induce a range of protective mechanisms for three different diseases. In this review paper, we discuss the rationale for and challenges to neonatal immunisation, summarising progress made in the field, including lessons learnt from newborn vaccines in the pipeline. Furthermore, we explore important maternal, infant and environmental co-factors that may impede the success of current and future neonatal immunisation strategies. A variety of approaches have been proposed to overcome the inherent regulatory constraints of the newborn innate and adaptive immune system, including alternative routes of delivery, novel vaccine configurations, improved innate receptor agonists and optimised antigen-adjuvant combinations. Crucially, a dual strategy may be employed whereby immunisation at birth is used to prime the immune system in order to improve immunogenicity to subsequent homologous or heterologous boosters in later infancy. Similarly, potent non-specific immunomodulatory effects may be elicited when challenged with unrelated antigens, with the potential to reduce the overall risk of infection and allergic disease in early life.

Lifetime Modulation of the Pain System via Neuroimmune and Neuroendocrine Interactions

Chronic pain is a debilitating condition that still is challenging both clinicians and researchers. Despite intense research, it is still not clear why some individuals develop chronic pain while others do not or how to heal this disease. In this review, we argue for a multisystem approach to understand chronic pain. Pain is not only to be viewed simply as a result of aberrant neuronal activity but also as a result of adverse early-life experiences that impact an individual's endocrine, immune, and nervous systems and changes which in turn program the pain system. First, we give an overview of the ontogeny of the central nervous system, endocrine, and immune systems and their windows of vulnerability. Thereafter, we summarize human and animal findings from our laboratories and others that point to an important role of the endocrine and immune systems in modulating pain sensitivity. Taking "early-life history" into account, together with the past and current immunological and endocrine status of chronic pain patients, is a necessary step to understand chronic pain pathophysiology and assist clinicians in tailoring the best therapeutic approach.

Neonatal vitamin D status is not associated with later risk of type 1 diabetes: results from two large Danish population-based studies

AIMS/HYPOTHESIS

The aim of this work was to assess whether neonatal levels of 25-hydroxyvitamin D (25(OH)D) are associated with risk of developing type 1 diabetes before the age of 18 years.

METHODS

Two large-scale studies with different designs-a case-cohort and a case-control-were conducted using Danish national register data and biobank material. Weighted Cox regression and conditional logistic regression were used to calculate HRs and ORs, respectively. The concentration of 25(OH)D was assessed from neonatal dried blood spots using highly sensitive liquid chromatography-tandem mass spectrometry. Quintiles of 25(OH)D3 were used in the main analyses.

RESULTS

The case-cohort study included 912 type 1 diabetes cases and 2866 individuals without type 1 diabetes born in Denmark between 1981 and 2002 and followed up until the end of 2012. The case-control study included 527 matched case-control pairs born between 1981 and 1999 and followed up until May 2004. Both studies found no association between 25(OH)D3 levels and later risk of developing type 1 diabetes. The neonatal total 25(OH)D levels in the studies were low: 46% (case-cohort study) and 51% (case-control study) of individuals had 25(OH)D levels <25 nmol/l.

CONCLUSIONS/INTERPRETATION

Our two large-scale national studies showed that 25(OH)D3 levels around the time of birth were not associated with later type 1 diabetes risk. Whether higher levels of 25(OH)D3 during pregnancy, acquired by higher doses of supplementation than are recommended today in most countries, could protect the offspring against type 1 diabetes cannot be ruled out by the present studies.

Human embryonic epidermis contains a diverse Langerhans cell precursor pool

Despite intense efforts, the exact phenotype of the epidermal Langerhans cell (LC) precursors during human ontogeny has not been determined yet. These elusive precursors are believed to migrate into the embryonic skin and to express primitive surface markers, including CD36, but not typical LC markers such as CD1a, CD1c and CD207. The aim of this study was to further characterize the phenotype of LC precursors in human embryonic epidermis and to compare it with that of LCs in healthy adult skin. We found that epidermal leukocytes in first trimester human skin are negative for CD34 and heterogeneous with regard to the expression of CD1c, CD14 and CD36, thus contrasting the phenotypic uniformity of epidermal LCs in adult skin. These data indicate that LC precursors colonize the developing epidermis in an undifferentiated state, where they acquire the definitive LC marker profile with time. Using a human three-dimensional full-thickness skin model to mimic in vivo LC development, we found that FACS-sorted, CD207(-) cord blood-derived haematopoietic precursor cells resembling foetal LC precursors but not CD14(+)CD16(-) blood monocytes integrate into skin equivalents, and without additional exogenous cytokines give rise to cells that morphologically and phenotypically resemble LCs. Overall, it appears that CD14(-) haematopoietic precursors possess a much higher differentiation potential than CD14(+) precursor cells.

Number of antigens in early childhood vaccines and neuropsychological outcomes at age 7-10 years

PURPOSE

Concerns have been raised that children may be receiving too many immunizations under the recommended schedule in the USA. We used a publicly available dataset to evaluate the association between antibody-stimulating proteins and polysaccharides from early childhood vaccines and neuropsychological outcomes at age 7-10 years.

METHODS

Children aged 7-10 years from four managed care organizations underwent standardized tests for domain-specific neuropsychological outcomes: general intellectual function, speech and language, verbal memory, attention and executive function, tics, achievement, visual spatial ability, and behavior regulation. Vaccination histories up to 24 months of age were obtained from medical charts, electronic records, and parents' records. Logistic regressions and structural equation modeling (SEM) were used to determine associations between total antigens up to 7, 12, and 24 months and domain-specific outcomes.

RESULTS

On average, children (N = 1047) received 7266, 8127, and 10 341 antigens by ages 7, 12, and 24 months, respectively. For adjusted analyses, increase (per 1000) in the number of antigens was not associated with any neuropsychological outcomes. Antigen counts above the 10th percentile, compared with lower counts, were also not associated with any adverse outcomes. However, children with higher antigen counts up to 24 months performed better on attention and executive function tests (odds ratio for lower scores = 0.51, 95% confidence interval = 0.26, 0.99). Similar results were found with SEM analysis (b = 0.08, p = 0.02).

CONCLUSIONS

We did not find any adverse associations between antigens received through vaccines in the first two years of life and neuropsychological outcomes in later childhood. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

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

Epigenetic modifications play a central role in the differentiation and function of immune cells in adult animals. Developmentally regulated epigenetic patterns also appear to contribute to the ontogeny of the immune system. We show here that the epigenetic profile of the T-helper (Th) 2 locus undergoes changes in T lineage cells beginning in mid-gestation and extending throughout the first week of life. In particular, regulatory regions of the Th2 locus are largely methylated at CpG residues among fetal liver common lymphoid progenitor cells. The locus subsequently becomes highly hypomethylated among the downstream progeny of these cells within the fetal thymus. This hypomethylated state is preserved until birth when the locus becomes rapidly re-methylated, achieving adult-like status by 3–6 days post birth. Notably, the capacity for rapid, high level Th2 cytokine production is lost in parallel with this re-methylation. In vitro organ culture and in vivo transplantation experiments indicate that signals from the adult environment are required to achieve the postnatal methylated state. Together, these findings indicate that the Th2 bias of neonates may be conferred, in part, by an epigenetic profile inherited from fetal life. However, the fetal program is rapidly terminated post birth by the development of signals leading to the acquisition of adult-like epigenetic patterns.

Validation of a Candida albicans delayed-type hypersensitivity (DTH) model in female juvenile rats for use in immunotoxicity assessments

Establishing an in vivo cell-mediated immunity (CMI) assay, such as the delayed-type hypersensitivity (DTH) assay, has been identified as an important gap and recommended to receive highest priority for new model development in several workshops on developmental immunotoxicity. A Candida albicans DTH model has recently been developed that has the advantage over other DTH models, which use alternative sensitizing antigens, in that antigen-specific antibodies, which may interfere with the assay, are not produced. In addition, the in vivo C. albicans DTH model was demonstrated to be more sensitive in detecting immunosuppression than DTH models using keyhole limpet hemocyanin (KLH) or sheep red blood cells as antigens, as well as some ex vivo CMI assays. While KLH and sheep red blood cells are non-physiological immunogens, C. albicans is an important human pathogen. The present studies were conducted in order to optimize and validate the C. albicans DTH model for use in developmental immunotoxicity studies using juvenile rats. Three known immunosuppressive compounds with different mechanisms of action were tested in this model, cyclosprorin A (CsA), cyclophosphamide (CPS), and dexamethasone (DEX). Animals were sensitized with formalin-fixed C. albicans on postnatal day (PND) 28 and challenged with chitosan on PND 38. Drug was administered beginning on PND 23 and continued until PND 37. Exposure to each of the three immunotoxicants resulted in statistically significant decreases in the DTH response to C. albicans-derived chitosan. Decreases in footpad swelling were observed at ≥10 mg CsA/kg/day, ≥5 mg CPS/kg/day, and ≥0.03 mg DEX/kg/day. These results demonstrate that the C. albicans DTH model, optimized for use in juvenile rats, can be used to identify immunotoxic compounds, and fills the need for a sensitive in vivo CMI model for assessments of developmental immunotoxicity. Abbreviations Ab, antibody APC, antigen presenting cell BSA, bovine serum albumin C. albicans, Candida albicans CI, challenge interval CMI, cell-mediated immunity CO, challenge only CPS, cyclophosphamide CsA, cyclosporin A CTL, cytotoxic T lymphocyte DEX, dexamethasone DIT, developmental immunotoxicity DTH, delayed-type hypersensitivity ip, intraperitoneal KLH, keyhole limpet hemocyanin MLR, mixed lymphocyte reaction OVA, ovalbumin PBS, phosphate-buffered saline PND, postnatal day sc, subcutaneous SEM, standard error of the mean SRBC, sheep red blood cells.

Phenotypic characterization of leukocytes in prenatal human dermis

The adult human skin harbors a variety of leukocytes providing immune surveillance and host defense, but knowledge about their ontogeny is scarce. In this study we investigated the number and phenotype of leukocytes in prenatal human skin (dermal dendritic cells (DDCs), macrophages, T cells (including FoxP3⁺ regulatory T cells), and mast cells) to unravel their derivation and to get a clue as to their putative function in utero. By flow cytometry and immunofluorescence, we found a distinction between CD206⁺CD1c⁺CD11c⁺ DDCs and CD206⁺CD209⁺CD1c⁻ skin macrophages by 9 weeks estimated gestational age (EGA). T cells appear at the end of the first trimester, expressing CD3 intracytoplasmatically. During midgestation, CD3⁺FoxP3⁻ and CD3⁺FoxP3⁺ cells can exclusively be found in the dermis. Similarly, other leukocytes such as CD117⁺ (c-kit) mast cells were not identified before 12–14 weeks EGA and only slowly acquire a mature phenotype during gestation. Our data show at which time point during gestation antigen-presenting cells, T cells, and mast cells populate the human dermis and provide a step forward to a better understanding of the development of the human skin immune system.

The emergence of adolescent onset pain hypersensitivity following neonatal nerve injury

Background

Peripheral nerve injuries can trigger neuropathic pain in adults but cause little or no pain when they are sustained in infancy or early childhood. This is confirmed in rodent models where neonatal nerve injury causes no pain behaviour. However, delayed pain can arise in man some considerable time after nerve damage and to examine this following early life nerve injury we have carried out a longer term follow up of rat pain behaviour into adolescence and adulthood.

Results

Spared nerve injury (SNI) or sham surgery was performed on 10 day old (P10) rat pups and mechanical nociceptive reflex thresholds were analysed 3, 7, 14, 21, 28, 38 and 44 days post surgery. While mechanical thresholds on the ipsilateral side are not significantly different from controls for the first 2–3 weeks post P10 surgery, after that time period, beginning at 21 days post surgery (P31), the SNI group developed following early life nerve injury significant hypersensitivity compared to the other groups. Ipsilateral mechanical nociceptive threshold was 2-fold below that of the contralateral and sham thresholds at 21 days post surgery (SNI-ipsilateral 28 (±5) g control groups 69 (±9) g, p < 0.001, 3-way ANOVA, n = 6 per group). Importantly, no effect was observed on thermal thresholds. This hypersensivity was accompanied by macrophage, microglial and astrocyte activation in the DRG and dorsal horn, but no significant change in dorsal horn p38 or JNK expression. Preemptive minocycline (daily 40 mg/kg, s.c) did not prevent the effect. Ketamine (20 mg/kg, s.c), on the other hand, produced a dose-dependent reversal of mechanical nociceptive thresholds ipsilateral to the nerve injury such that thresholds return to control levels at the highest doses of 20 mg/Kg.

Conclusions

We report a novel consequence of early life nerve injury whereby mechanical hypersensitivity only emerges later in life. This delayed adolescent onset in mechanical pain thresholds is accompanied by neuroimmune activation and NMDA dependent central sensitization of spinal nociceptive circuits. This delayed onset in mechanical pain sensitivity may provide clues to understand the long term effects of early injury such as late onset phantom pain and the emergence of complex adolescent chronic pain syndromes.

AAV-based neonatal gene therapy for hemophilia A: long-term correction and avoidance of immune responses in mice

Hemophilia A gene therapy has been hampered by immune responses to vector-associated antigens and by neutralizing antibodies or inhibitors to the factor VIII (FVIII) protein; these ‘inhibitors’ more commonly effect hemophilia A patients than those with hemophilia B. A gene replacement strategy beginning in the neonatal period may avoid the development of these immune responses and lead to prolonged expression with correction of phenotype thereby avoiding long-term consequences. Serotype rh10 AAV was developed splitting the FVIII coding sequence into heavy and light chains with the chicken β-actin promoter/CMV enhancer for dual recombinant AAV vector delivery. Coinjection of virions of each FVIII chain intravenously to mice on the second day of life was performed. Mice express sustained FVIII antigen levels of ≥5% to 22 months of life without the development of antibodies to FVIII. Phenotypic correction was manifest in all AAV-FVIII-treated mice as demonstrated by functional assay and reduction in bleeding time. This study demonstrates the use of AAV in a gene replacement strategy in neonatal mice that establishes both long-term phenotypic correction of hemophilia A and lack of antibody development to FVIII in this disease model where AAV is administered shortly after birth. These studies support consideration of gene replacement therapy for diseases that are diagnosed in utero or in the early neonatal period.

Reverse genetics generation of chimeric infectious Junin/Lassa virus is dependent on interaction of homologous glycoprotein stable signal peptide and G2 cytoplasmic domains

The Arenaviridae are a diverse and globally distributed collection of viruses that are maintained primarily by rodent reservoirs. Junin virus (JUNV) and Lassa virus (LASV) can both cause significant outbreaks of severe and often fatal human disease throughout their respective areas of endemicity. In an effort to improve upon the existing live attenuated JUNV Candid1 vaccine, we generated a genetically homogenous stock of this virus from cDNA copies of the virus S and L segments by using a reverse genetics system. Further, these cDNAs were used in combination with LASV cDNAs to successfully generate two recombinant Candid1 JUNV/LASV chimeric viruses (via envelope glycoprotein [GPC] exchange). It was found that while the GPC extravirion domains were readily exchangeable, homologous stable signal peptide (SSP) and G2 transmembrane and cytoplasmic tail domains were essential for correct GPC maturation and production of infectious chimeric viruses. The switching of the JUNV and LASV G1/G2 ectodomains within the Candid1 vaccine background did not alter the attenuated phenotype of the vaccine strain in a lethal mouse model. These recombinant chimeric viruses shed light on the fundamental requirements of arenavirus GPC maturation and may serve as a strategy for the development of bivalent JUNV and LASV vaccine candidates.

Yersinia enterocolitica promotes robust mucosal inflammatory T-cell immunity in murine neonates

Mucosal immunity to gastrointestinal pathogens in early life has been studied only slightly. Recently, we developed an infection model in murine neonates using the gastroenteric pathogen Yersinia enterocolitica. Here, we report that oral infection of neonatal mice with low doses of virulent Y. enterocolitica leads to vigorous intestinal and systemic adaptive immunity. Y. enterocolitica infection promoted the development of anti-LcrV memory serum IgG1 and IgG2a responses of comparable affinity and magnitude to adult responses. Strikingly, neonatal mesenteric lymph node CD4(+) T cells produced Yersinia-specific gamma interferon (IFN-gamma) and interleukin-17A (IL-17A), exceeding adult levels. The robust T- and B-cell responses elicited in neonates exposed to Y. enterocolitica were associated with long-term protection against mucosal challenge with this pathogen. Using genetically deficient mice, we found that IFN-gamma and CD4(+) cells, but not B cells, are critical for protection of neonates during primary Y. enterocolitica infection. In contrast, adults infected with low bacterial doses did not require either cell population for protection. CD4-deficient neonatal mice adoptively transferred with CD4(+) cells from wild-type, IFN-gamma-deficient, or IL-17AF-deficient mice were equally protected from infection. These data demonstrate that inflammatory CD4(+) T cells are required for protection of neonatal mice and that this protection may not require CD4-derived IFN-gamma, IL-17A, or IL-17F. Overall, these studies support the idea that Y. enterocolitica promotes the development of highly inflammatory mucosal responses in neonates and that intestinal T-cell function may be a key immune component in protection from gastrointestinal pathogens in early life.

Perinatal nutrition and immunity to infection

Epidemiological data provide strong evidence for a relationship between undernutrition and life-threatening infection in infants and children. However, the mechanisms that underlie this relationship are poorly understood. Through foetal life, infancy and childhood, the immune system undergoes a process of functional maturation. The adequacy of this process is dependent on environmental factors, and there is accumulating evidence of the impact of pre- and post-natal nutrition in this regard. This review outlines the impact of nutrition during foetal and infant development on the capacity to mount immune responses to infection. It provides an overview of the epidemiologic evidence for such a role and discusses the possible mechanisms involved.

Differential regulation of immune responses and macrophage/neuron interactions in the dorsal root ganglion in young and adult rats following nerve injury

BACKGROUND

Neuropathic pain is an apparently spontaneous experience triggered by abnormal physiology of the peripheral or central nervous system, which evolves with time. Neuropathic pain arising from peripheral nerve injury is characterized by a combination of spontaneous pain, hyperalgesia and allodynia. There is no evidence of this type of pain in human infants or rat pups; brachial plexus avulsion, which causes intense neuropathic pain in adults, is not painful when the injury is sustained at birth. Since infants are capable of nociception from before birth and display both acute and chronic inflammatory pain behaviour from an early neonatal age, it appears that the mechanisms underlying neuropathic pain are differentially regulated over a prolonged postnatal period.

RESULTS

We have performed a microarray analysis of the rat L4/L5 dorsal root ganglia (DRG), 7 days post spared nerve injury, a model of neuropathic pain. Genes that are regulated in adult rats displaying neuropathic behaviour were compared to those regulated in young rats (10 days old) that did not show the same neuropathic behaviour. The results show a set of genes, differentially regulated in the adult DRG, that are principally involved in immune system modulation. A functional consequence of this different immune response to injury is that resident macrophages cluster around the large A sensory neuron bodies in the adult DRG seven days post injury, whereas the macrophages in young DRG remain scattered evenly throughout the ganglion, as in controls.

CONCLUSIONS

The results show, for the first time, a major difference in the neuroimmune response to nerve injury in the dorsal root ganglion of young and adult rats. Differential analysis reveals a new set of immune related genes in the ganglia, that are differentially regulated in adult neuropathic pain, and that are consistent with the selective activation of macrophages around adult, but not young large A sensory neurons post injury. These differences may contribute to the reduced incidence of neuropathic pain in infants.

HLA-DR+ leukocytes acquire CD1 antigens in embryonic and fetal human skin and contain functional antigen-presenting cells

Adequate numbers and functional maturity are needed for leukocytes to exhibit a protective role in host defense. During intrauterine life, the skin immune system has to acquire these prerequisites to protect the newborn from infection in the hostile external environment after birth. We investigated the quantitative, phenotypic, and functional development of skin leukocytes and analyzed the factors controlling their proliferation and trafficking during skin development. We show that CD45⁺ leukocytes are scattered in embryonic human skin and that their numbers continuously increase as the developing skin generates an environment that promotes proliferation of skin resident leukocytes as well as the influx of leukocytes from the circulation. We also found that CD45⁺HLA-DR^highCD1c⁺ dendritic cells (DCs) are already present in the epidermis and dermis at 9 wk estimated gestational age (EGA) and that transforming growth factor β1 production precedes Langerin and CD1a expression on CD45⁺CD1c⁺ Langerhans cell (LC) precursors. Functionally, embryonic antigen-presenting cells (APCs) are able to phagocytose antigen, to up-regulate costimulatory molecules upon culture, and to efficiently stimulate T cells in a mixed lymphocyte reaction. Collectively, our data provide insight into skin DC biology and the mechanisms through which skin DCs presumably populate the skin during development.

Homeostasis and effector function of lymphopenia-induced "memory-like" T cells in constitutively T cell-depleted mice

Naive T lymphocytes acquire a phenotype similar to Ag-experienced memory T cells as a result of proliferation under lymphopenic conditions. Such "memory-like" T (T(ML)) cells constitute a large fraction of the peripheral T cell pool in patients recovering from T cell ablative therapies, HIV patients under highly active antiretroviral therapy, and in the elderly population. To generate a model that allows characterization of T(ML) cells without adoptive transfer, irradiation, or thymectomy, we developed genetically modified mice that express diphtheria toxin A under control of a loxP-flanked stop cassette (R-DTA mice). Crossing these mice to CD4Cre mice resulted in efficient ablation of CD4 single-positive thymocytes, whereas double-positive and CD8 single-positive thymocytes were only partially affected. In the periphery the pool of naive (CD44(low)CD62L(high)) T cells was depleted. However, some T cells were resistant to Cre activity, escaped deletion in the thymus, and underwent lymphopenia-induced proliferation resulting in a pool of T(ML) cells that was similar in size and turnover to the pool of CD44(high)CD62L(low) "memory phenotype" T cells in control mice. CD4Cre/R-DTA mice remained lymphopenic despite the large available immunological "space" and normal Ag-induced T cell proliferation. CD4Cre/R-DTA mice showed a biased TCR repertoire indicating oligoclonal T cell expansion. Infection with the helminth Nippostrongylus brasiliensis resulted in diminished effector cell recruitment and impaired worm expulsion, demonstrating that T(ML) cells are not sufficient to mediate an effective immune response.

Role of vitamin A elimination or supplementation diets during postnatal development on the allergic sensitisation in mice

Vitamin A (VA) and its derivatives, the retinoids, are important factors for the development of the immune system. It has been shown in adult animals that proliferation of lymphocyte populations and antibody secretion are retinoid dependent, while little is known about the effects of retinoids during postnatal development. The aim of this study was to investigate the role of VA on allergic sensitisation during lactation and after weaning using an in vivo system for postnatal allergic sensitisation in mice. Different VA diets (basal/VA elimination/VA (as retinyl palmitate) supplemented) were fed to the dams throughout lactation and directly to the pups after weaning. Allergic sensitisation was induced with a single peritoneal ovalbumin (OVA) injection at day 28 after weaning. The phenotype of lymphocytes was analysed by flow cytometry and functional data were obtained by analysis of (IL-4/IFN-gamma) cytokine production and antibody production (OVA-specific IgG1 and IgE) in the offspring. VA/retinyl palmitate supplementation during lactation and after weaning decreased CD3+, CD4+, CD8+ and B220+ populations in splenic lymphocytes but also significantly enhanced IL-4 production and OVA-specific IgE after sensitisation. In contrast, mice fed VA-elimination diet displayed no significant alteration of lymphocyte numbers and a slightly increased IL-4 production. Our results showed that a single allergen injection during postnatal development induces allergic sensitisation whose degree is modified by the VA content of the maternal diet during lactation and the diet of the pups after weaning, indicating an important role of VA on the severity of the allergic sensitisation.

Heterogeneity in the CD4 T Cell Compartment and the Variability of Neonatal Immune Responsiveness

Over the past decade, it has become clear that T cell immune responses in both murine and human neonates are very heterogeneous, running the gamut from poor or deviant responsiveness to mature, adult-like inflammatory function. How this variability arises is not well understood but there is now a great deal of information suggesting that differences in the T cell compartments in neonates vs adults play important roles. A number of cell types or processes are qualitatively or quantitatively different in the neonate. These include (a) alternate epigenetic programs at the Th2 cytokine locus, (b) enhanced homeostatic proliferation, (c) a relative abundance of fetal-origin cells, (d) a greater representation of recent thymic emigrants, (e) high proportions of potentially self-reactive cells, (f) a developmental delay in the production of regulatory T cells, and (g) cells bearing TCR with limited N region diversity. Different conditions of antigen exposure may lead to different environmental signals that promote the selective responsiveness of one or more of these populations. Therefore, the variability of neonatal responses may be a function of the heterogeneous nature of the responding T cell population. In this review, we will describe these various subpopulations in detail and speculate as to the manner in which they could contribute to the heterogeneity of neonatal immune responses.

Functional development of immune response in rabbits

The aim of our study was to extend knowledge concerning postnatal development of the immune system in rabbits from two aspects. Firstly, capability of lymphocytes from peripheral blood, spleen, mesenteric, and popliteal lymph nodes to respond to Concanavalin A stimulation was investigated. Secondly, changes in the ability to produce antibodies against tetanus toxoid by rabbits during maturation were studied. Proliferation of lymphocytes was reduced in mesenteric lymph nodes in newborns, in PB up to the age of two weeks, and in popliteal lymph nodes up to the age of four weeks when compared to adults. High spontaneous lymphocyte proliferation that lasted up to the age of two weeks was recorded in spleen. The study of antibody response showed that even one-day-old rabbits were able to form specific antibodies of isotype IgM and IgG. Nevertheless, significantly lower formation of both isotypes was noted in one-day and two-week-old rabbits, and commencement of IgG isotype formation was delayed in one-day, two-week, and four-week-old rabbits when compared to adults.

Murine neonates are highly resistant to Yersinia enterocolitica following orogastric exposure

Neonates are considered highly susceptible to gastrointestinal infections. This susceptibility has been attributed partially to immaturity in immune cell function. To study this phenomenon, we have developed a model system with murine neonates, using the natural orogastric route of transmission for the enteropathogen Yersinia enterocolitica. The susceptibilities of 7-day-old and adult mice to orogastric Y. enterocolitica infection were assessed in 50% lethal dose experiments. Remarkably, neonatal mice of either the BALB/c or C57BL/6 mouse strain showed markedly enhanced survival after infection compared to adult mice. The resistance of neonates was not due to failure of the bacteria to colonize neonatal tissues; Y. enterocolitica was readily detectable in the intestine and mesenteric lymph nodes (MLN) for at least 1 week after infection. In adult mice, Y. enterocolitica rapidly disseminated to the spleen and liver. In striking contrast, bacterial invasion of the spleen and liver in neonates was limited. Using flow cytometry and histology, we found substantial increases in the percentages of neutrophils and macrophages in the neonatal MLN, while influx of these cells into the adult MLN was limited. Similar results were obtained using two different high-virulence Y. enterocolitica strains. Importantly, depletion of neutrophils with a specific antibody led to increased translocation of the bacteria to the spleens and livers of neonates. Together, these experiments support the hypothesis that the neonatal intestinal immune system can rapidly mobilize innate phagocytes and thereby confine the bacterial infection to the gut, resulting in a high level of resistance.

The inflammatory and immune response to Helicobacter pylori infection

Lifelong Helicobacter pylori infection and its associated gastric inflammation underlie peptic ulceration and gastric carcinogenesis. The immune and inflammatory responses to H. pylori are doubly responsible: gastric inflammation is the main mediator of pathology, and the immune and inflammatory response is ineffective, allowing lifelong bacterial persistence. However, despite inducing gastric inflammation, most infections do not cause disease, and bacterial, host and environmental factors determine individual disease risk. Although H. pylori avoids many innate immune receptors, specific virulence factors (including those encoded on the cag pathogenicity island) stimulate innate immunity to increase gastric inflammation and increase disease risk. An acquired T helper 1 response upregulates local immune effectors. The extent to which environmental factors (including parasite infection), host factors and H. pylori itself influence T-helper differentiation and regulatory T-cell responses remains controversial. Finally, effective vaccines have still not been developed: a better understanding of the immune response to H. pylori may help.

Placental Plasmodium falciparum infection: causes and consequences of in utero sensitization to parasite antigens

Available evidence suggests that, in African populations, systemic blood-dwelling parasitoses of mothers are associated with enhanced susceptibility to infection of their offspring. Thus, children born to mothers with filariasis or schistosomiasis are infected earlier, and offspring of mothers with placental Plasmodium falciparum at delivery, commonly referred to as pregnancy-associated malaria or PAM, are themselves at higher risk of developing parasitaemia during infancy. Since foetal/neonatal antigen-presenting cells (APC) are either immature or provide insufficient costimulatory signals to T cells, thus favouring tolerance induction, it is commonly assumed that soluble parasite components [protein antigens], transferred transplacentally and inducing foetal immune tolerance, are largely, if not exclusively, responsible for these outcomes. Plasmodial asexual blood stage antigen-specific T cells are detectable in as many as two-thirds of all cord blood samples in malaria-endemic countries of sub-Saharan Africa, indicating that in utero sensitization may be a common phenomenon during pregnancy in these populations. Parasite antigen-specific T cell responses of neonates born to helminth-infected mothers display a highly skewed Th2-type cytokine pattern, with a prominent role for the regulatory cytokine interleukin (IL)-10. Similarly, the cord blood immune response of those born to mothers identified with on-going PAM is characterised by inducible parasite antigen-specific IL-10-producing regulatory T cells that can inhibit both APC HLA expression and Th1-type T cell responses. In contrast, plasmodial antigen-specific Th1-type responses, characterised by IFN-gamma production, predominate in cord blood of those born to mothers successfully treated for Pf malaria during gestation, suggesting that the duration and/or the nature of antigen exposure in utero governs the outcome with respect to neonatal immune responses. Aspects of APC function in the context of these differentially modulated responses, whether and how the latter translate into altered susceptibility to Pf infection during infancy, as well as the possible implications for vaccination in early life, are aspects that are discussed in this review.

Differing activation status and immune effector molecule expression profiles of neonatal and maternal lymphocytes in an African population

Higher susceptibility of newborns to infections has been attributed to the hypo-responsiveness of their cellular immune system. Here we compared the activation status and expression of cytokines and cytotoxic molecules of cord versus maternal peripheral blood mononuclear cells in an African population. Human leucocyte antigen-DR was expressed on a lower percentage of cord compared to maternal gammadelta and CD3(+) T cells. Similarly, a lower proportion of cord versus maternal gammadelta and CD3(+) T cells displayed perforin, granzyme B and cytokine activity either ex vivo or following non-specific stimulation in vitro. In contrast, comparable proportions of cord and maternal CD94(+) CD3(-) natural killer (NK) cells showed perforin and granzyme B expression ex vivo. We conclude that cord blood gammadelta and CD3(+) T cells are functionally hypo-responsive as reflected by reduced numbers of such cells expressing either an activation marker, T helper 1 (Th1) and Th2 cytokines or cytotoxic effector molecules. The similarity in numbers of cord and maternal CD94(+) CD3(-) cells expressing cytotoxic effector molecules suggests that neonatal Africans' NK cells may be functionally mature.

Early life T cell responses to pneumococcal conjugates increase with age and determine the polysaccharide-specific antibody response and protective efficacy

Immunization with a tetanus-protein (TT) pneumococcal polysaccharide (PPS) conjugate vaccine (Pnc1-TT) induces protective immunity against lethal pneumococcal infections in neonatal and infant mice, but anti-PPS IgG response and protective efficacy is lower than in adult mice. Here, we show that reduced antibody (Ab) response and protection against infections is directly related to impaired T cell response to the carrier. Whereas spleen cells from adult mice immunized with Pnc1-TT responded with proliferation and IFN-gamma secretion to in vitro stimulation with TT, spleen cells from neonatal and infant mice did not. However, significant, but age dependent, Th2-cytokine responses were observed in mice immunized with Pnc1-TT. Impaired IFN-gamma production upon TT-stimulation in vitro was also reflected in reduced IFN-gamma/IL-5 ratio. The IL--5 response correlated with IgG anti-PPS titers, and the lack of PPS Ab in the majority of neonatal mice was clearly associated with absence of carrier-specific IL-5 production. These results show that immunization with Pnc1-TT induces carrier-specific T cell responses that increase with age and determine the levels of PPS-specific Ab elicited. Whereas a weak and Th2-biased response was observed in neonatal mice, infant mice showed a mixed Th1-Th2 response as observed in adults.

Retinoid Concentrations in the Mouse during Postnatal Development and after Maternal Vitamin A Supplementation

BACKGROUND

Vitamin A (VA) and its derivates (retinoids) are important nutritional substances, which mediate their biological activity mainly via nuclear retinoid receptors. Maternal VA intake during lactation influences the VA content in milk and the VA status of the progeny. We investigated the effects of maternal supplementation during lactation and direct supplementation to the pups after weaning on the retinoid concentration in serum and liver of neonatal mice using high doses of VA.

METHODS

Dams were fed a basal (4,500 retinol equivalents/kg diet) or a VA-supplemented (324,000 retinol equivalents/kg diet) diet during lactation. Pups kept receiving the same diet after weaning. Serum and liver samples of the pups were collected during lactation at days 1, 3, 5, 7, and 14 and post-weaning at days 21 and 65 after birth. Samples were analysed for retinoids by high-performance liquid chromatography.

RESULTS

Maternal VA supplementation resulted in significantly higher concentrations of retinol, retinyl palmitate and retinyl stearate in serum of mice neonates at days 5, 7, 14, 21 and 65 after birth in comparison to the basal diet, whereas significantly higher concentrations were observed in liver at days 5, 14, 21 and 65 after birth. At day 7 after birth, a decrease in the liver retinoid concentrations occurred in the VA-supplemented diet.

CONCLUSION

Our results show for the first time that supplementation with high doses of VA during the lactation period in mice can affect serum retinol concentrations in the neonates and report that day 7 after birth is a critical time in the tissue distribution of retinoids during postnatal development.

In vitro HgCl2 exposure of immune cells at different stages of maturation: effects on phenotype and function

This is the first study to investigate the hypothesis that the immunotoxic effects of inorganic mercury may be modulated by inherent differences in the responsiveness of immune cells related to the age of the donor. We exposed cells from lymph nodes, spleen, and thymus, collected from 7- and 10-day-old CD.1 pups, as well as from adult CD.1 mice, in terms of the effects of mercury in vitro on responses to Con-A stimulation with respect to proliferation, cytokine production, and cell phenotype. The effects of mercury on proliferation were age and organ dependent, while effects on cytokine production were only age dependent. Effects of mercury were observed only on splenocyte T-cell subpopulations and only in cells from 10-day-old pups and from adults. Mercury had no effect on IFN-gamma and IL-4 production by splenocytes from 7-day-old pups, but significantly decreased release of these cytokines by splenocytes from 10-day-old pups and adults. Hg did not affect IL-4 production by lymph node cells or thymocytes. In lymph node cells Hg affected IFN-gamma production only at 7 days. These data indicate that inherent properties of immune cells at different stages of development may influence the response to immunotoxicants.

HSV induces an early primary Th1 CD4 T cell response in neonatal mice, but reduced CTL activity at the time of the peak adult response

Neonates are highly susceptible to HSV. In this study, we analyzed the primary neonatal cell-mediated response to HSV at the site of T cell activation, the draining lymph nodes (LN), and examined the effects of dose and the ability of HSV to replicate on the strength and character of this response. Neonatal mice mounted a predominantly Th1 cytokine (IFN-gamma) response at all doses of a replication-competent thymidine kinase-negative HSV-2 strain (186DeltaKpn) and at high doses of a replication-defective HSV-2 virus (dl5-29, UL5(-)/UL29(-)). Both neonates and adults showed increased production of Th2 cytokines (IL-4 and/or IL-5) at high doses of the replication-defective or inactivated HSV strains. An age-dependent difference in the strength of the Th1 response was noted, with neonates mounting adult-like responses at low but not high doses of HSV. Neonatal mice also showed impaired CD8(+) T cell activation and reduced HSV-specific CTL effector function at the time of the peak adult response. These studies are the first to highlight the impaired primary neonatal T cell response to HSV in the LN.

T cell homeostasis in tolerance and immunity

The size of the peripheral T cell pool is remarkably stable throughout life, reflecting precise regulation of cellular survival, proliferation, and apoptosis. Homeostatic proliferation refers to the process by which T cells spontaneously proliferate in a lymphopenic host. The critical signals driving this expansion are "space," contact with self-major histocompatibility complex (MHC)/peptide complexes, and cytokine stimulation. A number of studies have delineated an association between T cell lymphopenia, compensatory homeostatic expansion, and the development of diverse autoimmune syndromes. In the nonobese diabetic mouse model of type 1 diabetes, lymphopenia-induced homeostatic expansion fuels the generation of islet-specific T cells. Excess interleukin-21 facilitates T cell cycling but limited survival, resulting in recurrent stimulation of T cells specific for self-peptide/MHC complexes. Indeed, data from several experimental models of autoimmunity indicate that a full T cell compartment restrains homeostatic expansion of self-reactive cells that could otherwise dominate the repertoire. This review describes the mechanisms that govern T cell homeostatic expansion and outlines the evidence that lymphopenia presents a risk for development of autoimmune disease.

Animal models of sudden unexplained death

The etiology of sudden infant death syndrome (SIDS) is unknown but thought to be multifactorial. Several animal models have been developed that induce death without pre-existing symptoms and with pathology similar to that seen in SIDS infants; however, the relevance of these animal models to the events leading to SIDS remains elusive, in part because animal models are as varied as the potential causes of SIDS. In addition, it is difficult to find an animal model that can accurately reflect the genetic, developmental and environmental risk factors for SIDS. Comparisons between species can prove difficult but animal models provide a useful tool for evaluating potential mechanisms related to sudden unexplained death. This review focuses on models developed to examine the association of infection and inflammation with mechanisms proposed to explain sudden unexplained death.

Exposure to interferon-γ during synaptogenesis increases inhibitory activity after a latent period in cultured rat hippocampal neurons

Certain disorders of the nervous system may have their origin in disturbances in the development of synaptic connections and network structure that may not become overt until later in life. As inflammatory cytokines can influence synaptic activity in neuronal cultures, we analysed whether cytokine exposure during synaptogenesis can lead to imbalances in a neuronal network. Short-term application of interferon-gamma (IFN-gamma), but not tumour necrosis factor-alpha, during peak synaptogenesis (but not before or after) in Sprague-Dawley rat hippocampal cultures, caused both a decrease in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) and an increase in the frequency of spontaneous inhibitory postsynaptic currents (IPSCs). These effects were only detected in recordings made weeks later. This was not due to a depression of glutamatergic synapses or to a change in the relative number of neurons containing glutamic acid decarboxylase (GAD). There was an increase in the average amplitude of miniature IPSCs, and in GAD-expressing neurons the amplitude of miniature EPSCs were larger as well as the responses to glutamate. This indicates that IFN-gamma-treatment induced increased inhibition via postsynaptic changes. These effects of IFN-gamma treatment were not observed when neuronal nitric oxide synthase was inhibited. Our study therefore shows that exposure to IFN-gamma during a restricted period of development, which coincides with the peak of excitatory synaptogenesis, can cause progressive changes in synaptic activity in the network. Thus, cytokine exposure at a critical period of development may constitute a 'hit-and-run' mechanism for certain nervous system disorders that become manifest after a latency period.

Retinoid- and carotenoid-enriched diets influence the ontogenesis of the immune system in mice

Vitamin A (VA) has been identified as an important factor for the development of the immune system, especially during ontogenesis. It has been shown that antibody secretion and proliferation of lymphocyte populations depend on retinoids. In the present study we investigated the influence of a base VA diet and diets enriched with VA, beta-carotene and lycopene, on the ontogenesis of the immune system in mice. We examined the absolute and relative concentrations of splenic B lymphocytes (CD45R/B220), T lymphocytes (CD3+) and their subpopulations (CD4+ and CD8+), and measured serum immunoglobulin G (IgG) concentrations in the offspring of supplemented dams at different ages (1, 3, 5, 7, 14, 21 and 65 days). The experimental diets resulted in higher numbers of T and B lymphocytes after VA and carotenoid enrichment, when compared, at various time-points, with the base diet. Higher values of total serum IgG were found in the beta-carotene-enriched diet group on day 7. On days 7 and 14, the enriched diets induced significant alterations in the percentages and total numbers of splenic lymphocytes in comparison to the base diet. Our results confirm that supplementation with VA and carotenoids affect the immune-cell function during ontogenesis and suggest a possible role of these nutritional factors on the development of the immune system.

The antibody response to HBs antigen is regulated by coordinated Th1 and Th2 cytokine production in healthy neonates

A proportion of healthy neonates fail to produce protective levels of anti-HBs antibody following vaccination with recombinant hepatitis B vaccine. This study was undertaken to investigate contribution of Th1 and Th2 responses to anti-HBs antibody production and to explore the mechanism(s) of unresponsiveness to HBsAg in human neonates. Peripheral blood manonuclear cells (PBMCs) were isolated form 28 nonresponder (anti-HBs antibody <10 IU/l) and 25 responder neonates. The cells were stimulated in vitro with recombinant HBsAg and PHA mitogen and concentrations of IL-4, IL-10 and IFN-gamma were quantified in culture supernatants by sandwich ELISA. Our results demonstrated significantly increased production of all cytokines, including IL-4 (P < 0.001), IL-10 (P < 0.002) and IFN-gamma (P < 0.01) in responder compared to nonresponder vaccinees. No significant differences, however, were observed between the two groups of neonates in the levels of cytokines induced by PHA or secreted in absence of antigen and mitogen. Our findings suggest that unresponsiveness to recombinant HBsAg in healthy neonates is linked to inadequate secretion of both Th1 and Th2 cytokines.

The antibody response to HBs antigen is regulated by coordinated Th1 and Th2 cytokine production in healthy neonates

A proportion of healthy neonates fail to produce protective levels of anti-HBs antibody following vaccination with recombinant hepatitis B vaccine. This study was undertaken to investigate contribution of Th1 and Th2 responses to anti-HBs antibody production and to explore the mechanism(s) of unresponsiveness to HBsAg in human neonates. Peripheral blood manonuclear cells (PBMCs) were isolated form 28 nonresponder (anti-HBs antibody <10 IU/l) and 25 responder neonates. The cells were stimulated in vitro with recombinant HBsAg and PHA mitogen and concentrations of IL-4, IL-10 and IFN-gamma were quantified in culture supernatants by sandwich ELISA. Our results demonstrated significantly increased production of all cytokines, including IL-4 (P < 0.001), IL-10 (P < 0.002) and IFN-gamma (P < 0.01) in responder compared to nonresponder vaccinees. No significant differences, however, were observed between the two groups of neonates in the levels of cytokines induced by PHA or secreted in absence of antigen and mitogen. Our findings suggest that unresponsiveness to recombinant HBsAg in healthy neonates is linked to inadequate secretion of both Th1 and Th2 cytokines.

CD4-independent protective cytotoxic T cells induced in early life by a non-replicative delivery system based on virus-like particles

The relative immaturity of the neonatal immune system limits CD4(+) Th1 and cytotoxic T lymphocyte (CTL) responses, and represents a significant challenge for the development of vaccines against intracellular pathogens. In this report, we demonstrate the ability of a non-replicative delivery system based on parvovirus-like particles (VLP) to induce CTL responses in the neonatal period. A single immunization of 1-week-old BALB/c mice with recombinant VLP carrying a CD8(+) T cell determinant from lymphocytic choriomeningitis virus (VLP-LCMV) induced antigen-specific CD8(+) cytotoxic T cells that were similar to those elicited by adult immunization, as assessed by cytotoxic activity, interferon (IFN)-gamma secretion, cytotoxic precursor cell frequencies, in vitro avidity for antigen and protective activity against viral challenge. These CTL responses are elicited within 2 weeks of a single immunization, in the absence of adjuvant and independently of the presence and help of CD4(+) T cells, highlighting the potential of VLP as candidate vaccine vectors in early life.

Neonates support lymphopenia-induced proliferation

T cells expand without intentional antigen stimulation when transferred into adult lymphopenic environments. In this study, we show that the physiologic lymphopenic environment existing in neonatal mice also supports CD4 T cell proliferation. Strikingly, naive CD4 T cells that proliferate within neonates acquire the phenotypic and functional characteristics of memory cells. Such proliferation is inhibited by the presence of both memory and naive CD4 T cells, is enhanced by 3-day thymectomy, is independent of IL-7, and requires a class II MHC-TCR interaction and a CD28-mediated signal. CD44(bright) CD4 T cells in neonates have a wide repertoire as judged by the distribution of Vbeta expression. Thus, lymphopenia-induced T cell proliferation is a physiologic process that occurs during the early postnatal period.

Neonates mount robust and protective adult-like CD8(+)-T-cell responses to DNA vaccines

Neonates are thought to mount less vigorous adaptive immune responses than adults to antigens and infectious agents. This concept has led to a delay in the administration of many currently available vaccines until late infancy or early childhood. It has recently been shown that vaccines composed of plasmid DNA can induce both humoral and cell-mediated antimicrobial immunity when administered within hours of birth. In most of these studies, immune responses were measured weeks or months after the initial vaccination, and it is therefore questionable whether the observed responses were actually the result of priming of splenocytes within the neonatal period. Here we show that DNA vaccination at birth results in the rapid induction of antigen-specific CD8(+) T cells within neonatal life. Analyses of T-cell effector functions critical for the resolution of many viral infections revealed that neonatal and adult CD8(+) T cells produce similar arrays of cytokines. Furthermore, the avidities of neonatal and adult CD8(+) T cells for peptide and the rapidity with which they upregulate cytokine production after recall encounters with antigen are similar. Protective immunity against the arenavirus lymphocytic choriomeningitis virus, which is mediated by CD8(+) cytotoxic T cells, is also rapidly acquired within the neonatal period. Collectively these data imply that, at least in the case of CD8(+) T cells, neonates are not as immunodeficient as previously supposed and that DNA vaccines may be an effective and safe means of providing critical cell-mediated antiviral immunity extremely early in life.

Enhanced type 1 immunity after secondary viral challenge in mice primed as neonates

The goal of infant immunization against viral infection is to develop protective long term memory responses. Priming neonatal mice with a low dose of Cas-Br-E murine leukemia virus (Cas) results in adult-like, type 1 protective responses. However, other studies suggest that Ag priming of neonates leads to an increase in type 2 secondary responses even when primary responses were type 1. We assessed whether type 1 CD8+ T cell-mediated responses developed in murine neonates are maintained after secondary challenge with Cas in adulthood. Despite the induction of significant anti-viral CD8+-mediated cytotoxic T lymphocyte and IFN-gamma responses, initial neonatal priming led to a lower frequency of virus-specific T cells compared with adult priming. Adult frequencies were reached in mice primed as neonates only after secondary challenge in adulthood. A nonspecific and transient CD4+-mediated IL-4 response was present in all groups after secondary challenge with Cas or medium, indicating that this rise in type 2 cytokine production was not unique to mice that had been primed as neonates. Rather, type 1 anti-viral memory CD8+ T cell responses developed in neonatal mice are stable, protective, and enhanced after secondary challenge.

The phytoestrogen genistein induces thymic and immune changes: a human health concern?

Use of soy-based infant formulas and soy/isoflavone supplements has aroused concern because of potential estrogenic effects of the soy isoflavones genistein and daidzein. Here we show that s.c. genistein injections in ovariectomized adult mice produced dose-responsive decreases in thymic weight of up to 80%. Genistein's thymic effects occurred through both estrogen receptor (ER) and non-ER-mediated mechanisms, as the genistein effects on thymus were only partially blocked by the ER antagonist ICI 182,780. Genistein decreased thymocyte numbers up to 86% and doubled apoptosis, indicating that the mechanism of the genistein effect on loss of thymocytes is caused in part by increased apoptosis. Genistein injection caused decreases in relative percentages of thymic CD4(+)CD8(-) and double-positive CD4(+)CD8(+) thymocytes, providing evidence that genistein may affect early thymocyte maturation and the maturation of the CD4(+)CD8(-) helper T cell lineage. Decreases in the relative percentages of CD4(+)CD8(-) thymocytes were accompanied by decreases in relative percentages of splenic CD4(+)CD8(-) cells and a systemic lymphocytopenia. In addition, genistein produced suppression of humoral immunity. Genistein injected at 8 mg/kg per day produced serum genistein levels comparable to those reported in soy-fed human infants, and this dose caused significant thymic and immune changes in mice. Critically, dietary genistein at concentrations that produced serum genistein levels substantially less than those in soy-fed infants produced marked thymic atrophy. These results raise the possibility that serum genistein concentrations found in soy-fed infants may be capable of producing thymic and immune abnormalities, as suggested by previous reports of immune impairments in soy-fed human infants.

Oral DNA vaccination in utero induces mucosal immunity and immune memory in the neonate

Infectious diseases are responsible for a significant number of deaths during the first weeks of life. Some of the salient pathogens include HSV, HIV, hepatitis B virus, group B streptococcus, Haemophilus sp., and Chlamydia sp. The vertical transmission of many of these pathogens significantly increases the risk of neonatal infection. We recently reported that oral DNA immunization in utero induced high serum Ab titers and cell-mediated immunity in fetal lambs. In this study, we demonstrate immune memory and mucosal immunity in newborn lambs following oral DNA immunization of the fetus. A single oral exposure in utero to plasmid DNA encoding a truncated form of glycoprotein D of bovine herpesvirus-1 induced detectable immune responses in 80% (12 of 15) of newborn lambs. There was no evidence for the induction of immune tolerance in nonresponding lambs. Responding lambs displayed both systemic and mucosal immune responses and reduced virus shedding following intranasal challenge. Furthermore, strong anamnestic responses were evident for at least 3 mo after birth. The efficacy of in utero oral DNA immunization was further demonstrated with the hepatitis B surface Ag, and protective serum Ab titers occurred in 75% of immunized lambs. Thus, the present investigation confirms that oral DNA immunization in utero can induce both mucosal and systemic immune responses in the neonate and that this immunity has the potential to prevent vertical disease transmission.