Development of T-B cell collaboration in neonatal mice

The Neonatal Immune System and Respiratory Pathogens

Neonates are more susceptible to some pathogens, particularly those that cause infection in the respiratory tract. This is often attributed to an incompletely developed immune system, but recent work demonstrates effective neonatal immune responses to some infection. The emerging view is that neonates have a distinctly different immune response that is well-adapted to deal with unique immunological challenges of the transition from a relatively sterile uterus to a microbe-rich world, tending to suppress potentially dangerous inflammatory responses. Problematically, few animal models allow a mechanistic examination of the roles and effects of various immune functions in this critical transition period. This limits our understanding of neonatal immunity, and therefore our ability to rationally design and develop vaccines and therapeutics to best protect newborns. This review summarizes what is known of the neonatal immune system, focusing on protection against respiratory pathogens and describes challenges of various animal models. Highlighting recent advances in the mouse model, we identify knowledge gaps to be addressed.

Growth Hormone Improves Adipose Tissue Browning and Muscle Wasting in Mice with Chronic Kidney Disease-Associated Cachexia

Cachexia associated with chronic kidney disease (CKD) has been linked to GH resistance. In CKD, GH treatment enhances muscular performance. We investigated the impact of GH on cachexia brought on by CKD. CKD was induced by 5/6 nephrectomy in c57BL/6J mice. After receiving GH (10 mg/kg/day) or saline treatment for six weeks, CKD mice were compared to sham-operated controls. GH normalized metabolic rate, increased food intake and weight growth, and improved in vivo muscular function (rotarod and grip strength) in CKD mice. GH decreased uncoupling proteins (UCP)s and increased muscle and adipose tissue ATP content in CKD mice. GH decreased lipolysis of adipose tissue by attenuating expression and protein content of adipose triglyceride lipase and protein content of phosphorylated hormone-sensitive lipase in CKD mice. GH reversed the increased expression of beige adipocyte markers (UCP-1, CD137, Tmem26, Tbx1, Prdm16, Pgc1α, and Cidea) and molecules implicated in adipose tissue browning (Cox2/Pgf2α, Tlr2, Myd88, and Traf6) in CKD mice. Additionally, GH normalized the molecular markers of processes connected to muscle wasting in CKD, such as myogenesis and muscle regeneration. By using RNAseq, we previously determined the top 12 skeletal muscle genes differentially expressed between mice with CKD and control animals. These 12 genes' aberrant expression has been linked to increased muscle thermogenesis, fibrosis, and poor muscle and neuron regeneration. In this study, we demonstrated that GH restored 7 of the top 12 differentially elevated muscle genes in CKD mice. In conclusion, GH might be an effective treatment for muscular atrophy and browning of adipose tissue in CKD-related cachexia.

Vitamin C deficiency reveals developmental differences between neonatal and adult hematopoiesis

Hematopoiesis, a process that results in the differentiation of all blood lineages, is essential throughout life. The production of 1x10¹² blood cells per day, including 200x10⁹ erythrocytes, is highly dependent on nutrient consumption. Notably though, the relative requirements for micronutrients during the perinatal period, a critical developmental window for immune cell and erythrocyte differentiation, have not been extensively studied. More specifically, the impact of the vitamin C/ascorbate micronutrient on perinatal as compared to adult hematopoiesis has been difficult to assess in animal models. Even though humans cannot synthesize ascorbate, due to a pseudogenization of the L-gulono-γ-lactone oxidase (GULO) gene, its generation from glucose is an ancestral mammalian trait. Taking advantage of a Gulo^-/- mouse model, we show that ascorbic acid deficiency profoundly impacts perinatal hematopoiesis, resulting in a hypocellular bone marrow (BM) with a significant reduction in hematopoietic stem cells, multipotent progenitors, and hematopoietic progenitors. Furthermore, myeloid progenitors exhibited differential sensitivity to vitamin C levels; common myeloid progenitors and megakaryocyte-erythrocyte progenitors were markedly reduced in Gulo^-/- pups following vitamin C depletion in the dams, whereas granulocyte-myeloid progenitors were spared, and their frequency was even augmented. Notably, hematopoietic cell subsets were rescued by vitamin C repletion. Consistent with these data, peripheral myeloid cells were maintained in ascorbate-deficient Gulo^-/- pups while other lineage-committed hematopoietic cells were decreased. A reduction in B cell numbers was associated with a significantly reduced humoral immune response in ascorbate-depleted Gulo^-/- pups but not adult mice. Erythropoiesis was particularly sensitive to vitamin C deprivation during both the perinatal and adult periods, with ascorbate-deficient Gulo^-/- pups as well as adult mice exhibiting compensatory splenic differentiation. Furthermore, in the pathological context of hemolytic anemia, vitamin C-deficient adult Gulo^-/- mice were not able to sufficiently increase their erythropoietic activity, resulting in a sustained anemia. Thus, vitamin C plays a pivotal role in the maintenance and differentiation of hematopoietic progenitors during the neonatal period and is required throughout life to sustain erythroid differentiation under stress conditions.

Understanding Antibody Responses in Early Life: Baby Steps towards Developing an Effective Influenza Vaccine

The immune system of young infants is both quantitatively and qualitatively distinct from that of adults, with diminished responsiveness leaving these individuals vulnerable to infection. Because of this, young infants suffer increased morbidity and mortality from respiratory pathogens such as influenza viruses. The impaired generation of robust and persistent antibody responses in these individuals makes overcoming this increased vulnerability through vaccination challenging. Because of this, an effective vaccine against influenza viruses in infants under 6 months is not available. Furthermore, vaccination against influenza viruses is challenging even in adults due to the high antigenic variability across viral strains, allowing immune evasion even after induction of robust immune responses. This has led to substantial interest in understanding how specific antibody responses are formed to variable and conserved components of influenza viruses, as immune responses tend to strongly favor recognition of variable epitopes. Elicitation of broadly protective antibody in young infants, therefore, requires that both the unique characteristics of young infant immunity as well as the antibody immunodominance present among epitopes be effectively addressed. Here, we review our current understanding of the antibody response in newborns and young infants and discuss recent developments in vaccination strategies that can modulate both magnitude and epitope specificity of IAV-specific antibody.

Does age matter? The impact of rodent age on study outcomes

Rodent models produce data which underpin biomedical research and non-clinical drug trials, but translation from rodents into successful clinical outcomes is often lacking. There is a growing body of evidence showing that improving experimental design is key to improving the predictive nature of rodent studies and reducing the number of animals used in research. Age, one important factor in experimental design, is often poorly reported and can be overlooked. The authors conducted a survey to assess the age used for a range of models, and the reasoning for age choice. From 297 respondents providing 611 responses, researchers reported using rodents most often in the 6-20 week age range regardless of the biology being studied. The age referred to as 'adult' by respondents varied between six and 20 weeks. Practical reasons for the choice of rodent age were frequently given, with increased cost associated with using older animals and maintenance of historical data comparability being two important limiting factors. These results highlight that choice of age is inconsistent across the research community and often not based on the development or cellular ageing of the system being studied. This could potentially result in decreased scientific validity and increased experimental variability. In some cases the use of older animals may be beneficial. Increased scientific rigour in the choice of the age of rodent may increase the translation of rodent models to humans.

What Causes Biliary Atresia? Unique Aspects of the Neonatal Immune System Provide Clues to Disease Pathogenesis

Biliary atresia (BA) is the most frequent identifiable cause of neonatal cholestasis and the majority of patients will need liver transplantation for survival. Despite surgical intervention with the Kasai portoenterostomy, significant fibrosis and cirrhosis develops early in life. An increased understanding of what causes this inflammatory fibrosing cholangiopathy will lead to therapies aimed at protecting the intrahepatic biliary system from immune-mediated damage. This review focuses on studies pertaining to the role of the adaptive immune response in bile duct injury in BA, including cellular and humoral immunity. The neonatal presentation of BA begs the question of what are potential modifications of unique aspects of the neonatal immune system that "sets the stage" for the progressive biliary disease? Throughout this article, characteristics of the neonatal immune response are outlined and theories as to how alterations of this response could contribute to the pathogenesis of BA are discussed. These include aberrant Th1 and Th17 responses, deficiencies in regulatory T cells, activation of humoral immunity and autoimmunity. In order to advance our understanding of the etiology of BA, future studies should focus on those unique aspects of the neonatal immune system that have gone awry, as detailed throughout this review.

Postnatal and adult immunoglobulin repertoires of innate-like CD19(+)CD45R(lo) B Cells

The diversity in antibody repertoire relies on different B cell populations working efficiently to fulfil distinct specific functions. We recently described an innate-like CD19(+)CD45R(-/lo) (19(+)45R(lo)) cell population in postnatal unstimulated adult mice, a heterogeneous population containing cells expressing immunoglobulin M (IgM) and others behaving as differentiated mature B lymphocytes (intracytoplasmic IgG1, AID(+), Blimp-1(+)RAG2(-)). In the present study, we characterized the Ig repertoire expressed by splenic 19(+)45R(lo) cells, assuming that they would bear a restricted repertoire biased for germline rearrangements and low mutation rates similar to other innate-like cells. Sequences from 19(+)45R(lo) cells displayed a variety of V, D and J regions, and the analysis of the CDR-H3 region revealed an intermediate overall CDR-H3 length and moderate hydrophobicity. Both IgM and switched sequences of PD15 19(+)45R(lo) cells had shorter CDR-H3 region and fewer non-template N nucleotides than adult sequences, as expected for profiles that correspond to an immature phenotype. Regarding the mutation rate in the VH regions, IgG1 sequences already carried a high rate of replacement mutations at PD15, which increased further in the sequences obtained from adult mice. Moreover, statistical models suggest that a proportion of the switched sequences in adult 19(+)45R(lo) cells had experienced antigen selection, unlike other innate-like B cell compartments.

Neonatal antibody responses are attenuated by interferon-γ produced by NK and T cells during RSV infection

Respiratory syncytial virus (RSV) infects most children in the first year of life and is a major single cause of hospitalization in infants and young children. There is no effective vaccine, and antibody generated by primary neonatal infection is poorly protective against reinfection even with antigenically homologous viral strains. Studying the immunological basis of these observations in neonatal mice, we found that antibody responses to infection were low and unaffected by CD4 depletion, in contrast with adult mice, which had stronger CD4-dependent antibody responses. Natural killer cell depletion or codepletion of CD4(+) and CD8(+) cells during neonatal RSV infection caused a striking increase in anti-RSV antibody titer. These cells are major sources of the cytokine IFN-γ, and blocking IFN-γ also enhanced RSV-specific antibody responses in neonates. In addition, infection with a recombinant RSV engineered to produce IFN-γ reduced antibody titer, confirming that IFN-γ plays a pivotal role in inhibition of antibody responses after neonatal infection. These unexpected findings show that the induction of a strong cellular immune response may limit antibody responses in early life and that vaccines that induce IFN-γ-secreting cells might, in some situations, be less protective than those that do not.

Do viruses cause breast cancer?

Because mouse mammary tumor virus (MMTV; the Bittner virus) is the proven cause of breast cancer in both field and experimental mice, similar viruses have long been suspects as a potential cause of human breast cancer. MMTV-like viral genetic material has been identified in human breast tumors, but there is no definitive evidence whether MMTV is causal and not merely an innocuous infection in humans. High-risk human papilloma viruses (HPVs), Epstein-Barr (EBV), and other viruses also have been identified in human breast tumors, but again there is no definitive evidence for a causal role. Any viral hypothesis as a cause of breast cancer must take into account the most striking epidemiologic feature of human breast cancer, the three- to sixfold differences in mortality and up to eightfold differences in incidence between some Asian and Western populations. These differences dramatically lessen to a two- to threefold difference within one or two generations of migration of females from low to high risk of breast cancer countries. In this chapter, a plausible explanation for these phenomena is offered; that is, the hypothesis that oncogenic viruses such as MMTV and high-risk HPVs may initiate some breast cancers in most populations. Furthermore, dietary patterns are suggested to determine circulating sex hormone levels, which in turn promote the replication of the hormone-dependent viruses MMTV and HPV. In addition, diet and hormones promote growth of both normal and malignant cells. Finally, the hypothesis that migrants from low to high risk of breast cancer countries change their food consumption patterns is suggested, which leads to higher circulating hormone levels, which in turn promotes viral replication, which initiates breast oncogenesis, which is enhanced by sex and growth hormones.

Phenotype and function of neonatal DC

Newborns face complex physical and immunological changes before and after birth. Although the uterus is a sterile environment for the fetus, it also contains non-self material from the mother. Birth involves the transition from the sterile intra-uterine environment to an environment rich in microbes and requires rapid induction of appropriate responses to control these microbes. In this review we focus on the similarities and differences of human and murine neonatal DC and their reaction to various stimuli. A better understanding of the newborn immune system--in particular, the DC-T-cell interaction--will be beneficial for the development of improved strategies to prevent or treat infections in this vulnerable population and prepare the immune system to cope with allergens and tumors later in life.

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.

Viruses and human breast cancer

There are well-established risk factors for breast cancer, most of which relate to estrogens and growth hormones in females. These include early-age menarche, late-age menopause, postmenopausal obesity and use of hormone therapy. However, these factors do not account for the sixfold difference in breast cancer incidence and mortality between countries and the fact that these differences dramatically lessen after migration; nor do they account for male breast cancer. Accordingly, hormone-responsive viruses have become major suspects as etiological agents for human breast cancer. Human papillomaviruses, mouse mammary tumor virus and Epstein-Barr virus are the prime candidate viruses as causes of human breast cancer. Human papillomaviruses and the mouse mammary tumor virus have hormone responsive elements that appear to be associated with enhanced replication of these viruses in the presence of corticosteroid and other hormones. This biological phenomenon is particularly relevant because of the hormone dependence of breast cancer. Viral genetic material for each of these candidate viruses has been identified by polymerase chain reaction in breast tumors but rarely in normal breast tissue controls. Pooled data from controlled studies show substantial odds ratios for the presence of viral genetic material in breast tumors compared with normal controls. These and additional data provide substantial, but not conclusive, evidence that human papillomavirus, the mouse mammary tumor virus and Epstein-Barr virus may have a role in the etiology of human breast cancer. If conclusive evidence for a role of these viruses in breast carcinogenesis can be developed, there is a practical possibility of primary prevention.

The long-term but not the short-term antiviral effectof IFN-α depends on Flt3 ligand and pDC

The cooperation between IFN-alpha/beta and FL, the ligand of Fms-like tyrosine kinase 3 (Flt3), plays an important role in the defense against herpes simplex virus type 1 (HSV-1) in neonates. Treatment of neonatal mice with recombinant IFN-alpha has a short-term, FL-independent and a long-term, FL-dependent protective effect against HSV-1. In mice lacking FL, neonatal resistance against HSV-1 is very low and DC numbers in the spleen are reduced. The treatment of these mice with rIFN-alpha at day 6 resulted in an increased resistance against infection with HSV-1 at day 7. In C57BL/6 mice, treatment with rIFN-alpha at birth induced both FL and plasmacytoid DC (pDC), resulting in enhanced resistance against HSV-1 at day 7. In contrast, in mice lacking FL, IFN-alpha treatment at birth did not influence the splenic cell composition and had no effect on viral protection. The transfer of pDC to mice lacking FL enhanced viral resistance. Therefore, the induction and function of pDC, normally controlled by IFN-alpha/beta and FL, are decisive for viral resistance in neonatal mice.

Dendritic Cells from Mice Neonatally Vaccinated with Modified Vaccinia Virus Ankara Transfer Resistance against Herpes Simplex Virus Type I to Naive One-Week-Old Mice

Modified vaccinia Ankara (MVA) is an attenuated virus. MVA induces the production of IFN and Flt3-L (FL), which results in the expansion of dendritic cells (DC) and enhanced resistance against viral infections. We report on the interplay among IFN, FL, and DC in the resistance against heterologous virus after injection of neonatal mice with MVA. The induction of serum FL was tested on day 2, and the expansion of DC was tested 1 wk after treatment with MVA. At this time point the resistance against infection with heterologous virus was also determined. After MVA treatment, serum FL was enhanced, and DC, including plasmacytoid cells in spleen, were increased in number. Mice that lacked functional IFN type I and II systems failed to increase both the concentration of FL and the number of DC. Treatment with MVA enhanced resistance against HSV-1 in wild-type animals 100-fold, but animals without a functional IFN system were not protected. Transfer of CD11c(+) cells from MVA-treated mice into naive animals protected against lethal infection with HSV-1. Thus, although the increased resistance could be largely attributed to the increase in activation of IFN-producing plasmacytoid cells, this, in turn, depends on a complex interplay between the DC and T cell systems involving both FL and IFNs.

Impaired CD40-signalling in Langerhans' cells from murine neonatal draining lymph nodes: implications for neonatally induced cutaneous tolerance

Cutaneous tolerance to antigens may be induced in mice through application of antigen during the first few days following birth. The mechanism governing this neonatally induced tolerance remains uncertain. We employed a contact hypersensitivity model to analyse dendritic cell (DC) function and the expression of classical and non-classical lymphocyte populations within the neonate. Examination of draining lymph node DC after antigenic challenge of the skin revealed these DC to be significantly deficient in their ability to stimulate antigen-specific T cell proliferation. Co-stimulatory molecule (CD40, CD80 and CD86) expression of these cells was deficient in comparison to adult DC, and functional tests revealed these cells to possess a critical absence of CD40 signalling. A numerical analysis of classical and non-classical lymphocyte expression demonstrated that while the neonatal spleen is devoid of T cells, the lymph nodes have a normal repertoire of T, B, gammadelta and CD4+CD25+ lymphocytes but an increased expression of natural killer (NK) cells. This study indicates that functionally deficient DC are likely contributors to neonatally induced cutaneous tolerance.

Preconception maternal immunization to dust mite inhibits the type I hypersensitivity response of offspring

BACKGROUND

The maternal immunologic experience associated with early life exposure to allergens might contribute to the development of allergy during infancy.

OBJECTIVES

We sought to analyze the effect of the mother's immunization before conception with the dust mite Dermatophagoides pteronyssinus on the allergen priming and hypersensitivity response in early immunized offspring. The kinetics of D pteronyssinus immunization were observed from newborn to adult age, and the secondary response to D pteronyssinus was followed in offspring immunized in early life.

METHODS

Female A/Sn mice were immunized or not with D pteronyssinus and mated with male C57BL/6 mice. The hybrid offspring were immunized to investigate allotypes and subclasses of anti-D pteronyssinus antibody, as well as total IgE levels, by using ELISA and anti-D pteronyssinus IgE antibody by using the passive cutaneous anaphylaxis reaction. Ovalbumin was used for heterologous immunization. Cytokines were measured in the cell-culture supernatant by means of ELISA, and CD4(+)CD25(+) cells were analyzed by means of flow cytometry.

RESULTS

Offspring from immune mothers have not shown evidence of prenatal or postnatal allergen priming with respect to humoral level. Immunization with D pteronyssinus of offspring at very early life and in the postweaning period inhibited anti-D pteronyssinus IgE and IgG1 antibody production, along with the expected presence of maternal antibody. Furthermore, offspring antibody responsiveness from immune mothers has remained quiescent on secondary allergenic challenge. This maternal influence on the offspring antibody response was specific to D pteronyssinus because the immunization with a heterologous antigen did not alter IgE response. Maternal D pteronyssinus immunization induced a significant decrease of the IFN-gamma level in the offspring, avoided an exacerbation of T(H)2 cytokine secretion, and, concomitantly, upregulated the number of CD4(+)CD25(+) T cells.

CONCLUSION

Maternal immunization to D pteronyssinus seems to protect offspring from the development of allergy.

Immunity in neonates

Passively derived maternal immunity hampers active immunization of newborns. Further, an immature immune system contributes to a weak and Th2 polarized immunity. This state of immunity in early life sustains endemic infections in man and continuous reinfections in animal herds. The endemic infections of the young occur preferentially when the immune system is still functionally immature and when the low levels of maternal antibodies are no longer protective but yet blocks protective immune responses. Vaccines overcoming these problems would have strong positive effects on the herd health and environmental benefits. The Th2 bias of the newborn is mediated by high levels of progesterone and Th2 cytokines produced in the maternal-fetal interface. The activity of the innate system is enhanced in the mother during the prepartus period, certainly having effects on the offspring. Newborn, 2-days-old, mice can be primed with Sendai virus envelope proteins as model antigens to induce Th1 or Th2 responses, dependent on the supplementation of the virus antigen formulation with Th1 or Th2 adjuvants. This priming has a strong life-long effect when complemented with subsequent boosts. However and importantly this priming effect can be modulated by adjuvants focusing for Th1 and Th2 when applied to the mice at 6 weeks of age, i.e. when they are immunologically adult. It has been shown in various species, besides mice, i.e. dog, sheep, horse and seal, that a strong Th1 driving adjuvant can induce immune response and protection in newborns when conventional vaccines fail. In conclusion, the Th2 bias prevailing around partus can be overcome by appropriate immunological treatments, permitting effective vaccination and protective immunity in the newborn.

Neonatal and early life vaccinology

Preclinical and human vaccine studies indicate that, although neonatal immunisation does not generally lead to rapid and strong antibody responses, it may result in an efficient immunological priming, which can serve as an excellent basis for future responses. The apparent impairment of CD4 and CD8 T-cell function in early life seems to result from suboptimal antigen-presenting cells-T cell interactions, which can be overcome by use of specific adjuvants or delivery systems. Although persistence of maternal antibodies may limit infant antibody responses, induction of T-cell responses largely remain unaffected by these passively transferred antibodies. Thus, neonatal priming and early boosting with vaccine formulations optimised for sufficient early life immunogenicity and maximal safety profiles, could allow better control of the huge infectious disease burden in early life.

Neonatal immunity and somatic mutation

Neonatal animals are able to mount an effective immune response, both humoral and cellular, when immunized using conditions that maximize stimulation of antigen presenting cells, T cells, and B cells. In adults, somatic mutation is a key feature of the humoral immune response because it contributes to the generation of high affinity memory B cells. Recent evidence that B cells in neonatal mice and human infants can somatically mutate their immunoglobulin heavy chains suggests that neonates can utilize somatic mutation not only to diversify their restricted germline antibody repertoire, but also to improve upon this repertoire by the generation of B cells which can produce higher affinity antibodies. By extrapolation, if vaccination of children early in life resulted in somatic mutation and affinity maturation, this could provide a more protective antibody response to childhood diseases.