Selective impairment of TLR-mediated innate immunity in human newborns: neonatal blood plasma reduces monocyte TNF-alpha induction by bacterial lipopeptides, lipopolysaccharide, and imiquimod, but preserves the response to R-848

Neonates harbour highly active gammadelta T cells with selective impairments in preterm infants

Acknowledgement of the breadth of T-cell pleiotropy has provoked increasing interest in the degree to which functional responsiveness is elicited by environmental cues versus differentiation. This is particularly relevant for young animals requiring rapid responses to acute environmental exposure. In young mice, gammadelta T cells are disproportionately important for immuno-protection. To examine the situation in humans, we compared populations and clones of T cells from term and preterm babies, and adults. By comparison with alphabeta T cells, neonate-derived gammadelta cells show stronger, pleiotropic functional responsiveness, and lack signatory deficits in IFN-gamma production. Emphasising the acquisition of functional competence in utero, IFN-gamma was produced by gammadelta cells sampled from premature births, and, although one month's post-partum environmental exposure invariably increased their TNF-alpha production, it had no consistent effect on IFN-gamma or IL-2. In sum, gammadelta cells seem well positioned at birth to contribute to immuno-protection and immuno-regulation, possibly compensating for selective immaturity in the alphabeta compartment. With regard to the susceptibilities of preterm babies to viral infection, gammadelta cells from preterm neonates were commonly impaired in Toll-like receptor-3 and -7 expression and compared with cells from term babies failed to optimise cytokine production in response to coincident TCR and TLR agonists.

Neonatal enteral feeding tubes as loci for colonisation by members of the Enterobacteriaceae

Background

The objective of this study was to determine whether neonatal nasogastric enteral feeding tubes are colonised by the opportunistic pathogen Cronobacter spp. (Enterobacter sakazakii) and other Enterobacteriaceae, and whether their presence was influenced by the feeding regime.

Methods

One hundred and twenty-nine tubes were collected from two neonatal intensive care units (NICU). A questionnaire on feeding regime was completed with each sample. Enterobacteriaceae present in the tubes were identified using conventional and molecular methods, and their antibiograms determined.

Results

The neonates were fed breast milk (16%), fortified breast milk (28%), ready to feed formula (20%), reconstituted powdered infant formula (PIF, 6%), or a mixture of these (21%). Eight percent of tubes were received from neonates who were 'nil by mouth'. Organisms were isolated from 76% of enteral feeding tubes as a biofilm (up to 10⁷ cfu/tube from neonates fed fortified breast milk and reconstituted PIF) and in the residual lumen liquid (up to 10⁷ Enterobacteriaceae cfu/ml, average volume 250 μl). The most common isolates were Enterobacter cancerogenus (41%), Serratia marcescens (36%), E. hormaechei (33%), Escherichia coli (29%), Klebsiella pneumoniae (25%), Raoultella terrigena (10%), and S. liquefaciens (12%). Other organisms isolated included C. sakazakii (2%),Yersinia enterocolitica (1%),Citrobacter freundii (1%), E. vulneris (1%), Pseudomonas fluorescens (1%), and P. luteola (1%). The enteral feeding tubes were in place between < 6 h (22%) to > 48 h (13%). All the S. marcescens isolates from the enteral feeding tubes were resistant to amoxicillin and co-amoxiclav. Of additional importance was that a quarter of E. hormaechei isolates were resistant to the 3^rd generation cephalosporins ceftazidime and cefotaxime. During the period of the study, K. pneumoniae and S. marcescens caused infections in the two NICUs.

Conclusion

This study shows that neonatal enteral feeding tubes, irrespective of feeding regime, act as loci for the bacterial attachment and multiplication of numerous opportunistic pathogens within the Enterobacteriaceae family. Subsequently, these organisms will enter the stomach as a bolus with each feed. Therefore, enteral feeding tubes are an important risk factor to consider with respect to neonatal infections.

Skewed pattern of Toll-like receptor 4-mediated cytokine production in human neonatal blood: low LPS-induced IL-12p70 and high IL-10 persist throughout the first month of life

Newborns are highly susceptible to infectious diseases, which may be due to impaired immune responses. This study aims to characterize the ontogeny of neonatal TLR-based innate immunity during the first month of life. Cellularity and Toll-like receptor (TLR) agonist-induced cytokine production were compared between cord blood obtained from healthy neonates born after uncomplicated gestation and delivery (n=18), neonatal venous blood obtained at the age of one month (n=96), and adult venous blood (n=17). Cord blood TLR agonist-induced production of the Th1-polarizing cytokines IL-12p70 and IFN-alpha was generally impaired, but for TLR3, 7 and 9 agonists, rapidly increased to adult levels during the first month of life. In contrast, TLR4 demonstrated a slower maturation, with low LPS-induced IL-12p70 production and high IL-10 production up until the age of one month. Polarization in neonatal cytokine responses to LPS could contribute to neonatal susceptibility to severe bacterial infection.

Distinct roles of TLR4 and CD14 in LPS-induced inflammatory responses of neonates

During infections, pathogens bind to toll-like receptor (TLR)4 and CD14 receptors and induce cytokine release, leading to inflammation. Here, we investigated TLR4 and CD14 expression on peripheral blood leukocytes (PBLs) and their roles in lipopolysaccharide (LPS)-induced cytokine and chemokine release. Full-term and preterm neonates and adults were studied. PBLs were pretreated with anti-TLR4- and anti-CD14-blocking antibodies and stimulated with LPS. Cytokine and chemokine levels were measured in supernatants. TLR4, CD14 expression, and LPS-induced CXCL8 release were higher in neonates, possibly contributing to aberrant inflammation. TLR4 blockade resulted in approximately 3-fold greater suppression of LPS-induced CXCL8 release in preterm neonates (38%) than in adults (14%). CD14 blockade (approximately 80%) in neonates induced approximately 3-fold greater inhibition of CXCL8 release, compared with anti-TLR4 (approximately 30%). Anti-TLR4 partly (50-60%) inhibited IL-10 and TNF-alpha, whereas anti-CD14 completely suppressed their release. Our findings reveal that neonates depend more on TLR4 for CXCL8 release. Furthermore, neonatal LPS-induced CXCL8 release, apart from TLR4/CD14-mediated signaling, is regulated by LPS interactions with other TLRs and/or immune receptors. IL-10 and TNF-alpha release depends on LPS binding not only to CD14/TLR4 but also to CD14 associated with another TLR. Our findings reveal the contribution of TLR4 and CD14 in neonatal cytokine and chemokine release and could aid in design of antagonists to prevent harmful inflammation.

Intra-amniotic LPS modulation of TLR signaling in lung and blood monocytes of fetal sheep

Epidemiological studies suggest that intra-uterine exposure to inflammation may prime postnatal immune responses. In fetal sheep, intra-amniotic injection of lipopolysaccharide (LPS) induced chorioamnionitis, lung inflammation and maturation, matured lung monocytes to macrophages and initiated systemic tolerance of fetal monocytes to subsequent challenge with LPS. We hypothesized that LPS-mediated chorioamnionitis altered the response of lung and blood monocytes to Toll-like receptor (TLR) ligands such as PamCysK4 (TLR2), flagellin (TLR5), and human CpG-DNA (TLR9). Time-mated ewes were given intra-amniotic injections of LPS or saline. Blood and lung monocytes were assessed after 2 days, 7 days and 2 days and 7 days repetitive LPS injections before delivery at 124 days gestational age (term 150 days). Responsiveness of blood and lung monocytes to TLR-ligands in vitro was assessed by interleukin (IL)-6, tumor necrosis factor-alpha (TNF-alpha) and hydrogen peroxide. Monocytes from preterm controls had minimal responses. Lipopolysaccharide-mediated chorioamnionitis increased IL-6, TNF- alpha and hydrogen peroxide to all TLR agonists in blood and lung monocytes. Repetitive exposure to antenatal LPS reduced IL-6, TNF- alpha and hydrogen peroxide to TLR-ligands suggesting tolerance. Tolerance to TLR-ligands reduced IL-1 receptor associated kinase-4 expression. Thus, repeated fetal exposure to LPS induced tolerance to other TLR-ligands. These modulations of fetal innate immunity have implications for host defense and injury responses in preterm infants.

Bovine neonate natural killer cells are fully functional and highly responsive to interleukin-15 and to NKp46 receptor stimulation

Natural killer (NK) cells are key components of the innate immune system with their killing and cytokine producing abilities. Bovine NK cells have been characterized as NKp46⁺/CD3⁻ lymphocytes, but little is known about these cells in neonatal calves. As the newborn calf, with an insufficiently developed acquired immunity, has to employ the innate immune system, we wanted to investigate whether neonate NK cells had the same characteristics as cells from older calves. Freshly isolated neonate and calf NK cells presented the same resting CD2⁺/CD25^low/CD8^−/low phenotype. Neonates less than 8 days old had one third of the circulating NKp46⁺ cells of older calves, but the NK cells proliferated more actively in vitro in the presence of interleukin (IL)-2 or IL-15. Moreover, neonate NK cells were more cytotoxic both in an NKp46 mediated redirected lysis assay and in direct killing of a bovine cell line MDBK when cultured in the presence of IL-15. Neonate and calf NK cells cultured in the presence of IL-2 and then stimulated with IL-12 produced similar dose-dependent interferon (IFN)-γ amounts, while IL-15 cultured NK cells did not give such a response whatever the age. However, neonatal NK cells cultured in IL-15 and stimulated by IL-12 concomitantly with cross-linking of NKp46, produced 4 to 5 times more IFN-γ than calf NK cells. These data suggest that although present in lower number at birth, neonate NK cells are fully functional and are more responsive to IL-15 and activation through the NKp46 receptor than NK cells from older calves.

Neutrophil TLR4 expression is reduced in the airways of infants with severe bronchiolitis

Background:

In respiratory syncytial virus (RSV) bronchiolitis, neutrophils account for >80% of cells recovered from the airways in bronchoalveolar lavage (BAL) fluid. This study investigated neutrophil activation and Toll-like receptor (TLR) expression in the blood and lungs of infants with severe RSV bronchiolitis.

Methods:

BAL fluid and (blood) samples were collected from 24 (16) preterm and 23 (15) term infants ventilated with RSV bronchiolitis, and 12 (8) control infants. Protein levels and mRNA expression of CD11b, myeloperoxidase (MPO) and TLRs 2, 4, 7, 8 and 9 were measured in neutrophils.

Results:

Blood neutrophils had more CD11b in preterm and term infants with RSV bronchiolitis than control infants (p<0.025) but similar amounts of MPO. BAL fluid neutrophils from infants with RSV bronchiolitis had greater amounts of CD11b and MPO than blood neutrophils and BAL fluid neutrophils from controls (p<0.01). Blood neutrophils from term infants with RSV bronchiolitis had less total TLR4 protein than preterm infants with RSV bronchiolitis (p = 0.005), and both had less than controls (p<0.04). Total TLR4 for each group was greater in BAL fluid neutrophils than in blood neutrophils. Blood neutrophils from preterm infants with RSV bronchiolitis had greater TLR4 mRNA expression than term infants with RSV bronchiolitis (p = 0.005) who had similar expression to controls (p = 0.625).

Conclusions:

In infants with severe RSV bronchiolitis, neutrophil activation starts in the blood and progresses as they are recruited into the airways. Total neutrophil TLR4 remains low in both compartments. TLR4 mRNA expression is unimpaired. This suggests that neutrophil TLR4 expression is deficient in these infants, which may explain why they develop severe RSV bronchiolitis.

Induction and termination of inflammatory signaling in group B streptococcal sepsis

SUMMARY

Group B streptococcus (GBS) is part of the normal genital and gastrointestinal flora in healthy humans. However, GBS is a major cause of sepsis and meningitis in newborn infants in the Western world and an important pathogen in many developing countries. The dissection of the host response to GBS may increase the general understanding of innate immunity in sepsis, because newborn infants lack a sufficient adaptive response. Inflammatory signal induction in macrophages by GBS seems largely preserved in newborn infants, as shown both in vitro and in vivo. The engagement of Toll-like receptor 2 (TLR2) by lipoproteins and a myeloid differentiation factor 88 (MyD88)--dependent pathway induced by GBS cell wall are both important in this context. TLR2 activation of microglia by GBS induces neuronal damage, which might account for the high morbidity of GBS meningitis. At the same time, TLR2 mediates activation-induced cell death (AICD), a process involved in the containment of inflammation. In newborn infants, AICD and anti-bacterial polymorphonuclear leukocyte activity appears to be compromised. Accordingly, neonatal aberrations in the pathogen-specific negative control of inflammatory signaling are likely to contribute to excessive inflammation and neurological sequelae in GBS sepsis and meningitis.

Developmental biology of the innate immune response: implications for neonatal and infant vaccine development

Molecular characterization of mechanisms by which human pattern recognition receptors (PRRs) detect danger signals has greatly expanded our understanding of the innate immune system. PRRs include Toll-like receptors, nucleotide oligomerization domain-like receptors, retinoic acid inducible gene-like receptors, and C-type lectin receptors. Characterization of the developmental expression of these systems in the fetus, newborn, and infant is incomplete but has yielded important insights into neonatal susceptibility to infection. Activation of PRRs on antigen-presenting cells enhances costimulatory function, and thus PRR agonists are potential vaccine adjuvants, some of which are already in clinical use. Thus, study of PRRs has also revealed how previously mysterious immunomodulators are able to mediate their actions, including the vaccine adjuvant aluminum hydroxide that activates a cytosolic protein complex known as the Nacht domain leucine-rich repeat and pyrin domain-containing protein 3 inflammasome leading to interleukin-1beta production. Progress in characterizing PRRs is thus informing and expanding the design of improved adjuvants. This review summarizes recent developments in the field of innate immunity emphasizing developmental expression in the fetus, newborn, and infant and its implications for the design of more effective neonatal and infant vaccines.

A phase II, open-label study of the efficacy and safety of imiquimod in the treatment of superficial and mixed infantile hemangioma

OBJECTIVES

To explore the efficacy and safety of imiquimod 5% cream as a treatment for infantile hemangioma.

DESIGN

Phase II, open-label, noncomparative study of imiquimod applied during 16 weeks, with posttherapy follow-up 16 weeks later (8 months total).

SETTING

Outpatient pediatric tertiary care referral center in Quebec, Canada.

PARTICIPANTS

Healthy infants up to 8.8 months of age with previously untreated, nonulcerated, proliferative superficial or mixed infantile hemangioma, excluding periorbital, or perineal localization, > or =100 cm2 in size.

INTERVENTION

Topical imiquimod applied three to seven times per week for 16 weeks to infantile hemangioma.

MAIN OUTCOME MEASURES

Lesion area, volume, depth (Doppler ultrasound), and color (erythema), serum drug, and interferon-alpha levels.

RESULTS

Sixteen infants (11 girls, 5 boys) with a mean age at entry of 4.1 months and mean lesion area of 32.89 cm2, and volume of 39.98 cm3 were enrolled. Two participants discontinued treatment early, one for an adverse event (crying upon application), the other because of the lack of compliance. Local skin reactions were consistent with those reported in adults. Two cases had a decrease and three had an increase in lesion parameters; otherwise no meaningful changes in lesion area, volume, or depth were observed. At the 4-month posttreatment visit, 11 of 14 subjects had improvement in erythema (marginal homogeneity test = 2.668, p = 0.008). Measured serum drug and interferon-alpha levels were low or undetectable.

CONCLUSIONS

Treatment of infants with infantile hemangioma with imiquimod up to seven times per week for 16 weeks was generally well tolerated with low systemic exposure. Improvement was observed in hemangioma coloration, but not lesion size, suggesting effects were limited to the superficial component.

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.

The mother's immune system is a balanced threat to the foetus, turning to protection of the neonate

Immunological tolerance by the mother prevents rejection of the foetus, but aberrations may increase risk of abnormalities like spontaneous abortion, or foetal growth restriction. The neonate is normally colonized with mother's gut microflora, mainly composed of protective anaerobes. This least threatening form of microbial colonization of the neonate, is impaired by sectio delivery, but supported by breastfeeding. Mother's transplacental IgG, secretory IgA and other milk components help protect the neonate together with its own slowly expanding immune system.

CONCLUSION

The mother's immune system tolerates her foetus via several mechanisms. Failure to do so may cause foetal growth retardation, or spontaneous abortion. The mother and the neonate cooperate in preventing infections in the offspring.

Potential of immunomodulatory agents for prevention and treatment of neonatal sepsis

Prevention of neonatal infection-related mortality represents a significant global challenge particularly in the vulnerable premature population. The increased risk of death from sepsis is likely due to the specific immune deficits found in the neonate as compared to the adult. Stimulation of the neonatal immune system to prevent and/or treat infection has been attempted in the past largely without success. In this review, we identify some of the known deficits in the neonatal immune system and their clinical impact, summarize previous attempts at immunomodulation and the outcomes of these interventions, and discuss the potential of novel immunomodulatory therapies to improve neonatal sepsis outcome.

Two factors of the lectin pathway of complement, l-ficolin and mannan-binding lectin, and their associations with prematurity, low birthweight and infections in a large cohort of Polish neonates

Ficolins and one collectin, mannan-binding lectin (MBL), are the only factors known to activate the lectin pathway (LP) of complement. There is considerable circumstantial evidence that MBL insufficiency can increase susceptibility to various infections and influence the course of several non-infectious diseases complicated by infections. Much less information is available concerning l-ficolin. We report the results of a prospective study to investigate any association between either MBL deficiency or l-ficolin deficiency with prematurity, low birthweight or perinatal infections in a large cohort of Polish neonates, representing an ethnically homogenous population (n=1832). Cord blood samples were analysed to determine mbl-2 gene variants, MBL concentrations and MBL-MASP-2 complex activities (MBL-dependent lectin pathway activity) as well as l-ficolin levels. Median concentrations of l-ficolin and MBL were 2500 and 1124 ng/ml, respectively, while median LP activity was 272 mU/ml. After genotyping, 60.6% of babies were mbl-2 A/A, 35.4% were A/O and 4% were O/O genotypes. We found relative l-ficolin deficiency to be associated with prematurity, low birthweight and infections. l-Ficolin concentration correlated with gestational age and with birthweight, independently of gestational age. Preterm deliveries (<38 weeks) occurred more frequently among neonates with low LP activity but not with those having low serum MBL levels. Similarly, no association of serum MBL deficiency with low birthweight was found, but there was a correlation between LP activity and birthweight. Genotypes conferring very low serum MBL concentrations were associated with perinatal infections, and high-MBL-conferring genotypes were associated with prematurity. Our findings suggest that l-ficolin participates in host defence during the perinatal period and constitute the first evidence that relative l-ficolin deficiency may contribute to the adverse consequences of prematurity. Some similar trends were found with facets of MBL deficiency, but the observed relationships were weaker and less consistent.

Basal and stimulus-induced cytokine expression is selectively impaired in peripheral blood mononuclear cells of newborn foals

Neonates are thought to be generally deficient in production of Th-1-associated cytokines at birth, and thereby more susceptible to bacterial infections. Using neonatal foals as a model, this study examined the age-dependent maturation of both basal and stimulus-induced immune responses, as reflected by the expression of a panel of Th-1-associated and pro-inflammatory cytokines. Results showed that although the basal production of IFN-gamma and IL-6 was impaired (P<0.05) in PBMCs of neonatal foals at birth, the basal production of IL-8, IL-12(p35/p40) and IL-23(p19/p40) were either in excess of or comparable to that of older foals. In response to Rhodococcus equi and CpG-ODN stimulation in vitro, PBMCs of neonatal foals showed increased (P<0.05) expression of IFN-gamma and IL-6, and preferentially increased expression of either IL-23(p19/p40) with R. equi stimulation or IL-12(p35/p40) with CpG-ODN stimulation. The magnitude of these stimulus-induced responses (except for IL-23p19), were significantly (P<0.05) less for newborn foals than for older foals. The selective impairment of age-dependent basal and stimulus-induced cytokine expression by newborn foals may reflect the different functional state of various TLR pathways in newborns, and be directly associated with their age-dependent susceptibility to infection. Our results indicate that CpG-ODNs can selectively stimulate deficient cytokines (P<0.05) from PBMCs in newborn foals in vitro, suggesting immunoprophylactic or therapeutic potential of CpG-ODNs.

Allogeneic transplantation successfully corrects immune defects, but not susceptibility to colitis, in a patient with nuclear factor-kappaB essential modulator deficiency

BACKGROUND

Boys with X-linked ectodermal dysplasia and immunodeficiency caused by mutations of nuclear factor-kappaB essential modulator have defects in innate and adaptive immunity, and some have colitis.

OBJECTIVE

We sought to determine whether curing the immune defect in such patients by means of allogeneic hematopoietic stem cell transplantation abolishes the susceptibility to colitis.

METHODS

A boy with X-linked hypohydrotic ectodermal dysplasia with immunodeficiency underwent allogeneic transplantation from a matched unaffected sibling identified by means of preimplantation genetic diagnosis. Toll-like receptor (TLR) function was assessed by measuring TLR agonist-induced cytokine production in whole blood tested in vitro. B-cell proliferation was measured by means of tritiated thymidine incorporation. Natural killer cell function was examined in PBMCs by means of K562 target cell lysis. Colitis severity was assessed clinically based on corticosteroid requirement and histology of large intestinal biopsy specimens.

RESULTS

Defects in cytokine production in response to TLR agonists, CD40-mediated proliferation, and natural killer cell cytotoxicity were all corrected after hematopoietic stem cell transplantation. Despite successful hematopoietic and immune reconstitution, the patient continued to have flares of colitis, often associated with bacterial infection.

CONCLUSIONS

Our findings strongly suggest that nuclear factor-kappaB essential modulator deficiency intrinsic to the intestinal epithelium is sufficient to predispose to colitis, despite robust correction of immune defects.

Impairment of T helper and T regulatory cell responses at birth

BACKGROUND

There is strong evidence that reduced exposures to microbial compounds triggering innate immune responses early in life are critical for the development of allergic illnesses. The underlying mechanisms remain unknown, but will include T-cell responses either along T helper type 1 (Th1)/Th2 pathways or via T regulatory and Th17 cells. Yet, little is known about innate immune responses and the function of T regulatory/Th17 cells at birth. The aim of this study was to investigate T-cell responses to innate (Lipid A/LpA, peptidoglycan/Ppg) and adaptive (phytohemagglutinin) stimuli at birth and to compare these findings with adult immune responses.

METHODS

Cord and peripheral blood mononuclear cells including T regulatory and Th17 cells from 25 neonates and 25 adults were examined for proliferation, cytokine secretion, surface, mRNA expression and functional suppression assays.

RESULTS

Proliferation and cytokine responses to innate stimuli were less mature at birth than in adulthood. T regulatory and Th17 cells were less expressed in cord than in adult blood (Ppg-induced Foxp3, P = 0.001, LpA-induced CD4(+) CD25(+) high, P = 0.02; Th17 : P < 0.0001). Mitogen-induced suppression of T-regulatory cells on T-effector cell function was less efficient in cord than in adult blood (P = 0.01). At both ages, Th17 cells were correlated with Th1/Th2 cells (P < 0.01), but not with interleukin-10 secretion following innate-stimulation.

CONCLUSION

Innate immune responses are immature at birth. Furthermore, the function of T regulatory and Th17 cells is impaired. Th17 cells in association with Th1/Th2 cells may be involved in early immuno-modulation. Potent innate immune stimulation early in life can potentially contribute to protection from allergic diseases.

Application of six-color flow cytometry for the assessment of dendritic cell responses in whole blood assays

Analysis of peripheral blood dendritic cells (PBDCs) is increasingly reaching clinical relevance in a wide range of pathologies, in which investigating the capacity of DC subsets to respond adequately to specific stimuli may aid the comprehension of underlying immunopathologic mechanisms. The evaluation of PBDC responses directly challenged in whole blood (WB) samples offers many advantages over other methods that require DC isolation and culture, but it is limited in multiparametric analysis, currently based on 3- or 4-color assays. Therefore, in this study we developed a 6-color assay dedicated to the analysis of PBDC responses upon WB stimulation. We incubated WB samples with ligands to toll-like receptors (TLRs) with a clear-cut distribution on myeloid DCs (mDCs) or plasmacytoid (pDCs) and analyzed DC responses in terms of upregulation of activation/maturation markers, as well as production of a wide range of regulatory cytokines. Four colors were used to gate on mDCs and pDCs that were identified as lineage-/HLA-DR+/CD11c+ and lineage-/HLA-DR+/CD123+, respectively, and two further colors were used to analyze either the surface expression of CD80, CD86, CD40 or CD83, or the intracellular accumulation of IL-12, tumor-necrosis factor (TNF)-alpha, interferon (IFN)-alpha, IL-6, IL-10 or IL-4. With this method, we could directly compare in the same flow cytometric tube the responses of mDCs and pDCs to TLR stimulation, and investigate the reciprocal coexpression of distinct activation markers or regulatory cytokines. We suggest that the 6-color WB assay presented here may represent a novel tool for investigating the complex biology of DCs.

Developmental and epigenetic regulation of the human TLR3 gene

The receptor encoded by the human TLR3 gene recognizes double-strand RNAs (dsRNAs) associated with viral infection. TLR3 expression is strongly activated upon differentiation of monocytes to dendritic cells, and can be further stimulated by the dsRNA analog polyinosine:polycytosine (PI:C). We report evidence for developmental regulation of the TLR3 gene. In dendritic cells derived from cord blood, both differentiation- and PI:C-associated TLR3 transcriptional activation are impaired as compared to cells from adults. Consistent with relative expression patterns, chromatin states and remodeling differ between newborn and adult samples. TLR3 expression in newborn dendritic cells exhibits heterocellularity and allelic imbalance (skewing), features characteristic of cis-acting epigenetic control. These findings reveal a new source for variability in innate immune system function and provide a model for further study of perinatal epigenetic transitions during development.

Phenotypic differences between cord blood and adult peripheral blood

BACKGROUND AND OBJECTIVES

Neonates are more susceptible to infections than adults, due to a less mature immune system. The objective of this study was to compare the immunophenotypes of cord blood (CB) and adult peripheral blood (APB) and to establish whether or not there are immunophenotypical differences.

METHODS

CB and APB were collected into CPD anticoagulant. Whole blood was stained with fluorochrome conjugated antibodies, cells were fixed, red cells were lysed, and samples were run in a FACSCanto flow cytometer.

RESULTS

Plots of SSC vs. CD45 showed two lymphocyte-like populations in CB with the same low SSC characteristics while there was only one low SSC lymphoid population in APB. The CD45dim population included the majority of CD34+ cells, but it also included T, B, NKT, and NK cells. The percentages of CD3+, CD3+CD4+, CD3+CD8+, CD19+, CD3+CD56+, and CD3-CD56+ in the CD45high gate of CB were similar to the percentages obtained for APB. Meanwhile, in the CD45dim gate, the percentages were either lower (CD3+, CD3+CD4+, CD3+CD8+) or higher (CD19+, CD3+CD56+, CD3-CD56+) than in the CD45high gate.

CONCLUSIONS

CB presents two lymphoid populations defined by different levels of expression of the phosphatase CD45; the CD45dim subsets likely represent cells with elevated proliferative activity possibly due to the differential expression of CD45 but still not yet immunologically mature with regard to immunophenotype and function.

Defective innate immunity predisposes murine neonates to poor sepsis outcome but is reversed by TLR agonists

Neonates exhibit an increased risk of sepsis mortality compared with adults. We show that in contrast to adults, survival from polymicrobial sepsis in murine neonates does not depend on an intact adaptive immune system and is not improved by T cell-directed adaptive immunotherapy. Furthermore, neonates manifest an attenuated inflammatory and innate response to sepsis, and have functional defects in their peritoneal CD11b(+) cells. Activation of innate immunity with either a Toll-like receptor 4 (TLR4) or TLR7/8 agonist, but not a TLR3 agonist, increased the magnitude, but abbreviated the early systemic inflammatory response, reduced bacteremia, and improved survival to polymicrobial sepsis. TLR4 agonist pretreatment enhanced peritoneal neutrophil recruitment with increased oxidative burst production, whereas the TLR7/8 agonist also enhanced peritoneal neutrophil recruitment with increased phagocytic ability. These benefits were independent of the adaptive immune system and type I interferon signaling. Improving innate immune function with select TLR agonists may be a useful strategy to prevent neonatal sepsis mortality.

Increased mortality and altered immunity in neonatal sepsis produced by generalized peritonitis

Neonates have a higher prevalence of bacterial sepsis and have greater morbidity and mortality from sepsis than other infants and children. Our understanding of the inflammatory and immunological responses to sepsis is hampered by the lack of appropriate neonatal murine models. In the present report, we have developed a cecal slurry model of generalized peritonitis in neonatal mice (age range, 5-7 days) and compared the outcome and the innate and adaptive cellular responses of these animals with those of the young adult animals (age range, 7-10 weeks) with sepsis induced either by cecal slurry administration or by cecal ligation and puncture. Neonatal mice were more susceptible to sepsis and mounted a markedly attenuated systemic inflammatory response compared with young adult animals (specifically, decreased plasma interferon gamma; interleukins 1alpha and 1beta; regulated on activation, normal T expressed and secreted (RANTES); and tumor necrosis factor alpha concentrations). Compared with young adult animals, septic neonatal mice did not lose significant percentage or absolute number of splenic CD4+ T cells. These findings suggest that the cecal slurry model of generalized peritonitis can produce sepsis in neonatal mice with dose-dependent lethality. Inherent differences in the host response to polymicrobial sepsis between neonatal and young adult animals may explain the increased sensitivity of the neonatal mouse to generalized peritonitis.

Hyper innate responses in neonates lead to increased morbidity and mortality after infection

Neonates suffer high morbidity and mortality in infection, presumably because of the lack of a fully developed adaptive and innate immune system. Evidence of poor innate responses in neonates has been shown by using a model that sensitizes the host to Toll-like receptor (TLR)-mediated inflammation with d-galactosamine (d-GalN). However, we show that neonatal mice demonstrate much stronger inflammatory responses than adult mice in response to LPS stimulation, and such hypersensitivity extends to other TLR agonists including actual viral infection. Our study reveals that the ensuing inflammatory reaction after d-GalN sensitization reflects preferential toxicity of d-GalN to adult liver cells, rather than accurately reflecting the TLR response to LPS. We show further that an uncontrolled proinflammatory innate response due to inadequate T cells makes neonates more vulnerable to TLR agonists or viral infection. Remarkably, through transfer of T cells into neonates or depletion of T cells in adult mice, we show that T cells are sufficient and necessary to control the early inflammatory response to LPS. Therefore, neonates might suffer from the unleashed innate responses caused by an insufficient number of T cells, which leads to increased morbidity and mortality.

Neonatal goats display a stronger TH1-type cytokine response to TLR ligands than adults

In mammals, Toll-like receptors play a critical role in initiating innate immune responses and modulating adaptive immunity, by recognizing conserved microbial molecular patterns. This study was undertaken to identify specific features of the responses to synthetic toll-like receptor (TLR) agonists in goats, for the definition of tailored immunostimulation strategies. We show here, in contrast to what has been shown in mice, that mesenteric lymph nodes (MLNs) cells and splenocytes from neonatal goats produce much higher levels of TH1-type cytokines than adults in response to various TLR agonists. IL-12 was identified as a critical cytokine for IFNgamma production by CD8(+) neonatal cells. The higher level of IL-12 production by neonatal MLN and spleen cells than by adult cells was not correlated with a higher level of TLR expression or lower levels of production of the regulatory cytokine IL-10. In neonates, two cell populations-class II(+) CD8(+) and class II(+) CD8(-) cells-produce IL-12 in response to R848 and Poly I:C, respectively. Thus, goat kids have characteristics that could be exploited to favor development of the TH1-type responses critical for the control of intracellular pathogens.

Necrotizing enterocolitis: A multifactorial disease with no cure

Necrotizing enterocolitis is an inflammatory bowel disease of neonates with significant morbidity and mortality in preterm infants. Due to the multifactorial nature of the disease and limitations in disease models, early diagnosis remains challenging and the pathogenesis elusive. Although preterm birth, hypoxic-ischemic events, formula feeding, and abnormal bacteria colonization are established risk factors, the role of genetics and vasoactive/inflammatory mediators is unclear. Consequently, treatments do not target the specific underlying disease processes and are symptomatic and surgically invasive. Breast-feeding is the most effective preventative measure. Recent advances in the prevention of necrotizing enterocolitis have focused on bioactive nutrients and trophic factors in human milk. Development of new disease models including the aspect of prematurity that consistently predisposes neonates to the disease with multiple risk factors will improve our understanding of the pathogenesis and lead to discovery of innovative therapeutics.

Immunostimulatory activity of Toll-like receptor 8 agonists towards human leucocytes: basic mechanisms and translational opportunities

TLR8 (Toll-like receptor 8) is activated by ssRNAs (single-stranded RNAs) and synthetic imidazoquinoline compounds that resemble purines and have immunostimulatory activity. TLR8 agonists are particularly effective at inducing Th1-polarizing responses from human monocytes and myeloid dendritic cells, with the magnitude of response substantially exceeding that induced by agonists of other TLRs. Mechanisms underlying the remarkable efficacy of TLR8 agonists may include: (i) particularly robust activation of intracellular signalling cascades culminating in nuclear translocation of NF-kappaB (nuclear factor kappaB), (ii) activation of BTK (Bruton's tyrosine kinase), and (iii) the ability of some imidazoquinolines to induce TLR-independent effects via antagonism of adenosine receptors. The strong agonist activities of TLR8 agonists also extend to human neonatal leucocytes, which usually display impaired Th1-polarizing responses to many diverse stimuli including agonists of other TLRs. Their strong Th1-polarizing properties render TLR8 agonists attractive targets of biopharmaceutical development as agents that may induce protective immune responses in diverse populations, including newborns.

Analysis of toll-like receptor-dependent production of proinflammatory cytokines in vitro by human peripheral blood mononuclears of donors and patients with primary immunodeficiency

The production of TNF-alpha and IFN-alpha cytokines by peripheral blood mononuclears in response to stimulation by TLR2/6, TLR4, TLR5, TLR9 ligands (zymosan, LPS, flagellin, and CpG-oligodeoxynucleotide, respectively) was studied in donors and patients with common variable immunodeficiency. Individual characteristics of TNF-alpha production by mononuclears were revealed in donors. Reduced stimulated production of TNF-alpha in response to stimulation with TLR4 and TLR5 ligands in vitro was detected in patients with common variable immunodeficiency.

Invasive Candida species disease in infants and children: occurrence, risk factors, management, and innate host defense mechanisms

PURPOSE OF REVIEW

Invasive infections by opportunistic Candida species significantly impact morbidity and mortality. This review provides an update of the incidence, risk factors, and management of invasive candidal disease in infants and children, focusing on very-low-birth-weight neonates, and highlights recent advances in understanding candidal virulence factors and innate anti-Candida species host defense mechanisms.

RECENT FINDINGS

Invasive infections with Candida species are the most common cause of late-onset, blood culture-proven nosocomial sepsis in very-low-birth-weight neonates. Risk factors include colonization, long stay in neonatal intensive care units, and use of broad-spectrum antibiotics, central venous catheters, parenteral nutrition, and mechanical ventilation. These risks are compounded by increasing resistance of Candida species to standard antifungal agents. Recent data suggest that, in addition to the macrophage mannose receptor, beta-glucan receptors, Toll-like receptors, and galectin-3 play an important role in host recognition of Candida species.

SUMMARY

Reduction of proven risk factors, more aggressive eradication of colonizing fungi by anticandidal agents, and possibly Candida species vaccines may reduce Candida species-associated morbidity and mortality. Accumulating data of molecular mechanisms that underlie innate immune functions against Candida species may provide a basis to prevent and treat candidal infections more efficiently.

Genetic polymorphisms of viral infection-associated Toll-like receptors in Chinese population

Toll-like receptors (TLRs) play a pivotal role in an innate immunity system, which controls inflammation responses and further instructs development of adaptive immunity. We enrolled 250 Han Chinese in Taiwan screening for the single nucleotide polymorphisms (SNPs) in TLRs associated with viral infection, including TLR2, TLR3, TLR4, TLR7, TLR8, and TLR9. The 6 SNPs not hitherto identified in Chinese populations, including TLR3 1377 C>T, TLR3 -7 C>A, TLR7 Gln11Leu, TLR7 IVS1+1817 G>T, TLR8 Met1Val, and TLR8 -129 G>C, had minor allele frequencies of 38%, 23%, 22.3%, 3%, 16.0%, and 16.0%, respectively. The frequencies of 2 common SNPs, TLR9, -1486 T>C and 2848 G>A, were 28% and 44%, respectively. As compared with other ethnic populations, Chinese displayed an opposite allele frequency of TLR8 Met1Val and TLR8 -129 G>C to Caucasians and African Americans. In addition, TLR2 Arg677Try, TLR2 Arg753Gln, TLR4 Asp299Gly, and TLR4 Thr399Ile that were apparent in approximately 10% of Caucasians were not detected in Chinese. In conclusion, obvious ethnic differences in TLR polymorphisms may in part reflect the ethnic diversity of host viral susceptibility.

Postnatal development of monocyte cytokine responses to bacterial lipopolysaccharide

Early childhood is a period of heightened susceptibility to infection due to immaturity of the immune system, and the nature of these developmental deficiencies is only partially understood. In this study, we focused on the ontogeny of the innate immune system by investigating the capacity of mononuclear cells to secrete a wide spectrum of inflammatory cytokines in response to interferon (IFN)-gamma priming and lipopolysaccharide (LPS) stimulation, namely IL-6, IL-10, IL-12, IL-18, IL-23, tumor necrosis factor (TNF)-alpha, and myxovirus resistance protein A, induced by type-I IFN, at several time points between birth (cord blood) and adulthood. Competence to produce all these cytokines followed a similar developmental pattern, with slow postnatal up-regulation from the response observed in cord blood. Unexpectedly, IL-6, IL-10, TNF-alpha, and IFN-gamma showed slow postnatal up-regulation but also elevated cord blood responses equal to or greater than the adult level. This was transient and not observed at 2 mo of age, and was not related to predelivery stress of the newborns. Variations in Toll-like receptor (TLR)4 function may account for these age related differences in cytokine responses, as TLR4 expression on neonatal monocytes post LPS stimulation was elevated and sustained relative to infants and adults.

Langerhans Cell Receptors

Langerhans cells (LC) are a subtype of dendritic cells, which reside in the epidermis. LCs are antigen-presenting cells that originate in bone marrow and enter the epidermis through blood vessels. LCs exhibit a variety of antigen receptors that are able to respond to a wide range of antigens. Within the last two decades, these receptors have been the subject of considerable research. This article focuses on the rapidly growing body of knowledge with respect to the functions of LC receptors.

Neonatal B cells suppress innate toll-like receptor immune responses and modulate alloimmunity

It has been known for decades that neonates are susceptible to transplant tolerance, but the immunological mechanisms involved remain to be fully elucidated. Recent evidence indicates that the maturation state of DCs responding to an allograft may have a profound impact on whether immunity or tolerance ensues. Given that TLR activation is a key process leading to DC maturation, we hypothesized that DCs from neonates have defective TLR immune responses. Contrary to our hypothesis, we found that murine neonatal DCs demonstrated enhanced TLR responses in comparison to adult counterparts in vitro. However, we found that neonatal B cells possess unique immunoregulatory functions as they impaired DC responses to TLR activation in an IL-10-dependent fashion. Functionally, we demonstrated that TLR-activated neonatal, but not adult, B cells impaired Th1, but not Th2, T cell alloimmune responses in vitro and in vivo, in models of alloimmune priming and allotransplantation. We conclude that neonatal B cells possess unique immunoregulatory properties that inhibit DC function and modulate alloimmunity in our murine experimental systems.

Combined Toll-like receptor agonists synergistically increase production of inflammatory cytokines in human neonatal dendritic cells

Dendritic cells (DC) are thought to be responsible for the reduced ability of human newborns to induce protective T-helper 1 (Th1) immune responses. The key player in Th1 differentiation, interleukin-12 (IL-12), is primarily produced in response to Toll-like receptor (TLR) binding by adult DC but not by neonatal DC. The potential use of various TLR agonist combinations for initiating neonatal monocyte-derived DC to prime Th1 responses was investigated. Single TLR ligands induced maturation only in adult DC; neonatal DC matured with combined targeting of TLR3/TLR8 or TLR4/TLR8, based on the expression of maturation markers. Similarly, the synergistic effects of combined TLR ligands could also be shown with adult and neonatal cytokine production, but different expression patterns were noted. In particular, IL-12p70 was produced by neonatal DC exclusively after combined TLR stimulation. Surprisingly, it was found that supernatants of combined stimulated neonatal DC could induce interferon-gamma production in autologous naïve T cells. Moreover, this interferon-gamma secretion was blocked by anti-IL-12p70 antibodies and increased after addition of recombined IL-12. In conclusion, these findings underline the differences between adult and neonatal DC and might suggest new strategies for promoting newborn Th1 immunity in response to pathogens and vaccine antigens.

Neonatal immune responses to coagulase-negative staphylococci

PURPOSE OF REVIEW

Coagulase-negative staphylococci have emerged as the most common nosocomial pathogen in neonatal intensive care units worldwide. Our understanding of the interactions between coagulase-negative staphylococci and the immune system is incomplete, especially in the newborn. This review summarizes current knowledge on the human immune response to coagulase-negative staphylococci, with particular emphasis on the neonatal innate immune system.

RECENT FINDINGS

There are very limited data on innate immune responses to coagulase-negative staphylococci in neonates. Levels of serum proteins, including transplacental anti-coagulase-negative staphylococci immunoglobulin and complement, correlate with gestational age, and this relative deficiency in preterm infants contributes to their suboptimal opsonization and impaired bacterial killing of coagulase-negative staphylococci. In adults, coagulase-negative staphylococci elicit significant cytokine responses in vitro, which are probably partly mediated by Toll-like receptors, including Toll-like receptor type 2, but these pathways have not been characterized in the high-risk neonatal population.

SUMMARY

The susceptibility of human preterm neonates to coagulase-negative staphylococci relates partly to the immaturity of the neonatal immune response. Strategies to reduce the burden of coagulase-negative staphylococci infections require a thorough understanding of host-pathogen interactions, particularly the engagement of coagulase-negative staphylococci by the neonatal innate immune system.

Innate immunity of the newborn: basic mechanisms and clinical correlates

The fetus and newborn face a complex set of immunological demands, including protection against infection, avoidance of harmful inflammatory immune responses that can lead to pre-term delivery, and balancing the transition from a sterile intra-uterine environment to a world that is rich in foreign antigens. These demands shape a distinct neonatal innate immune system that is biased against the production of pro-inflammatory cytokines. This bias renders newborns at risk of infection and impairs responses to many vaccines. This Review describes innate immunity in newborns and discusses how this knowledge might be used to prevent and treat infection in this vulnerable population.

Negative regulation of TLR9-mediated IFN-alpha induction by a small-molecule, synthetic TLR7 ligand

Toll-like receptors (TLRs) are a family of molecules that function as sensors for the detection of foreign pathogens through the recognition of nonvariable microbial motifs. Although numerous studies have focused on singular TLRs, less attention has been focused on how simultaneous signaling of multiple TLRs may result in counter-regulation of the effects of each. Here, we examine the counter-regulation that occurs during simultaneous stimulation of TLR7 and TLR9 on human plasmacytoid dendritic cells (PDCs) and B cells. Interestingly, we observed that the capacity for potent IFN-alpha-induction by TLR9 ligands like CpG-C and CpG-A is markedly reduced by concurrent small molecule TLR7 stimulation. However, this inhibition is specific to particular CpG motif-containing immunostimulatory sequence (ISS) functions such as IFN-alpha induction and BDCA-2 down-regulation. Other ISS activities such as PDC expression of CD80/CD86, secretion of IL-6, and B cell proliferation are not altered by the presence of TLR7 ligands (TLR7Ls). In concordance with the ability of TLR7Ls to decrease IFN-alpha secretion induced by ISS, we also find that the expression of interferon regulatory factor-7 (IRF-7), a transcriptional factor critical for IFN-alpha expression, is reduced. Furthermore, down-regulation of TLR9 mRNA expression is accelerated after TLR7 stimulation. These data indicate that TLR7 and TLR9 costimulation do not combine synergistically for IFN-alpha induction and demonstrate that, instead, a negative feedback mechanism has evolved, possibly to prevent levels of IFN-alpha secretion potentially detrimental to the host.

Immune responsiveness in the neonatal period

The maintenance of pregnancy requires suppression of the maternal immune system which would naturally recognize the developing fetus as an allograft and seek to destroy it by mounting a Th1 regulated cytotoxic immune response. During pregnancy a range of soluble factors are produced by the placenta which switch maternal immune regulation towards a protective Th2 phenotype. These factors also influence the developing fetal immune system and all newborns initially have an immunological milieu skewed towards Th2 immunity. Vaccination during the neonatal period must therefore overcome the dual challenge of the inhibitory effect of maternally derived antibody and this natural Th2 regulatory environment. One means of overcoming these obstacles is by the use of adjuvant systems that can redirect the neonatal immune response towards an appropriate Th1 regulated reaction that affords protection from infectious disease. In this overview, experiments are described in which viral antigens incorporated into immune stimulatory complexes (ISCOMs) are able to induce immune responses with balanced Th1 and Th2 regulation in neonatal mice, as evidenced by the nature of the IgG subclass response and cytokine profile, and the induction of cytotoxic lymphocytes. ISCOM adjuvanted vaccines are able to induce similar protective immunity in the newborn of larger animal species including cattle, horses and dogs.

Molecular mechanisms underlying anti-inflammatory phenotype of neonatal splenic macrophages

Neonatal humans and rodents are susceptible to infection with encapsulated bacteria as a result of an inability to make antibodies to capsular polysaccharides. This is partly a result of decreased production of proinflammatory cytokines by splenic macrophages (MPhi) from neonates. In this study, we show that when stimulated with a variety of agonists to TLR2, -4, and -9, neonatal MPhi make less proinflammatory cytokines and more IL-10 than adult MPhi. IL-10 appears to have a role in the decreased proinflammatory cytokine production, as neonatal MPhi treated with anti-IL-10 receptor antibody or from IL-10(-/-) mice produced levels of proinflammatory cytokines at a level comparable with that produced by adult MPhi. A microarray analysis of RNA from resting and LPS-stimulated MPhi from neonatal and adult mice showed that expression of a large number of genes encoding cytokines, chemokines, and their receptors was decreased dramatically in the neonatal MPhi, although some cytokines, including IL-10 and IL-16, were enhanced. Several genes in the TLR signaling pathway leading to NF-kappaB activation were down-regulated, which may account for the decreased chemokine and cytokine synthesis. It is surprising that p38alpha MAPK, known to be required for TLR-induced cytokine secretion, was enhanced in the neonatal MPhi. Our studies with the p38 MAPK inhibitor SB203580 suggested that excess p38 MAPK activity can be inhibitory for TLR2-, -4-, and -9-induced production of proinflammatory cytokines but not IL-10. The anti-inflammatory phenotype of the neonatal Mphi may be unique to the developing organism, although it compromises the neonate's ability to respond to encapsulated bacteria.

Type I interferons protect neonates from acute inflammation through interleukin 10-producing B cells

Newborns and infants are highly susceptible to viral and bacterial infections, but the underlying mechanism remains poorly understood. We show that neonatal B cells effectively control the production of proinflammatory cytokines by both neonatal plasmacytoid and conventional dendritic cells, in an interleukin (IL) 10-dependent manner, after Toll-like receptor (TLR) 9 triggering. This antiinflammatory property of neonatal B cells may extend to other TLR agonists (Pam3CSK4, lipopolysaccharide, and R848) and viruses. In the absence of B cells or of CD5(+) B cell subsets, neonatal mice developed stronger inflammatory responses and became lethally susceptible to CpG challenge after galactosamine sensitization, whereas wild-type (WT) mice were resistant. Paradoxically, interferon (IFN)-alpha/beta enhanced the inflammatory response to CpG challenge in adult mice, whereas they helped to control neonatal acute inflammation by stimulating the secretion of IL-10 by neonatal B cells. Finally, WT neonatal B cells rescued IL-10(-/-) neonates from a lethal CpG challenge, whereas IFN-alpha/beta receptor-deficient B cells did not. Our results show that type I IFNs support a negative regulatory role of neonatal B cells on TLR-mediated inflammation, with important implications for neonatal inflammation and infection.

Maternal smoking in pregnancy: do the effects on innate (toll-like receptor) function have implications for subsequent allergic disease?

Subtle increases in immaturity of immune function in early infancy have been implicated in the rising susceptibility to allergic disease, particularly relative impairment of type 1 interferon (IFN)-γ responses in the neonatal period. Although genetic predisposition is a clear risk factor, the escalating rates of allergic disease in infancy suggest that environmental factors are also implicated. We previously showed that maternal smoking in pregnancy may impair neonatal IFN-γ responses. Our more recent studies now indicate that this common avoidable toxic exposure is also associated with attenuation of innate immune function, with attenuated Toll-like receptor (TLR)-mediated microbial responses (including TLR-2, -3, -4, and -9 responses). Most notably, the effects were more marked if the mothers were also allergic. In this review, we discuss the significance of these observations in the context of the emerging hypothesis that variations in TLR function in early life may be implicated in allergic propensity. There is now growing evidence that many of the key pathways involved in subsequent T-cell programming and regulation (namely, antigen-presenting cells and regulatory T cells) rely heavily on microbe-driven TLR activation for maturation and function. Factors that influence the function and activity of these innate pathways in early life may contribute to the increasing predisposition for allergic disease. Although "cleaner" environments have been implicated, here we explore the possibility that other common environmental exposures (such as maternal smoking) could also play a role.

Allergic disorders in African countries: linking immunology to accurate phenotype

Identification and characterization of risk and protective factors for allergy is important for developing strategies for prevention or treatment. The prevalence of allergy is clearly higher in affluent countries than in developing countries like, e.g. Africa. Especially in urban areas of developing countries, allergy is however on the increase. In Africa, we have the unique opportunity to investigate risk and protective factors and the influence of urbanization and westernization, i.e. almost to take a look at Europe, Australia or the USA as they were before their allergy epidemics. Moreover, migrants from developing to affluent countries experiencing an increased burden of allergy provide new insights into risk and protective factors. Allergen exposure, diet and infections are the major exogenous influences playing a role as risk and protective factors. Depending on the nature, timing, chronicity and level of exposure, each of them can promote or inhibit allergy. Perhaps with the exception of infections, availability of data from Africa on their role in the development of allergy is limited. Detailed epidemiological studies in rural and urban Africa combined with basic immunological research are needed to unravel mechanisms of increase in allergy and of protection. The maturation of the immune system at young age under influence of exogenous factors results in differences in T-cell-skewing (Th1/Th2/Treg) and humoral responses. It is essential to perform studies from a 'non-Eurocentric' angle (e.g. local allergens, locally validated questionnaires and diagnostic procedures). Such studies will provide the affluent countries with new leads to combat the allergy epidemic and more importantly help prevent it in Africa.

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 effect of CpG-ODN on antigen presenting cells of the foal

Background

Cytosine-phosphate-guanosine oligodeoxynucleotide (CpG-ODN) has been used successfully to induce immune responses against viral and intracellular organisms in mammals. The main objective of this study was to test the effect of CpG-ODN on antigen presenting cells of young foals.

Methods

Peripheral blood monocytes of foals (n = 7) were isolated in the first day of life and monthly thereafter up to 3 months of life. Adult horse (n = 7) monocytes were isolated and tested once for comparison. Isolated monocytes were stimulated with IL-4 and GM-CSF (to obtain dendritic cells, DC) or not stimulated (to obtain macrophages). Macrophages and DCs were stimulated for 14–16 hours with either CpG-ODN, LPS or not stimulated. The stimulated and non-stimulated cells were tested for cell surface markers (CD86 and MHC class II) using flow cytometry, mRNA expression of cytokines (IL-12, IFNα, IL-10) and TLR-9 using real time quantitative RT-PCR, and for the activation of the transcription factor NF-κB p65 using a chemiluminescence assay.

Results

The median fluorescence of the MHC class II molecule in non-stimulated foal macrophages and DCs at birth were 12.5 times and 11.2 times inferior, respectively, than adult horse cells (p = 0.009). That difference subsided at 3 months of life (p = 0.3). The expression of the CD86 co-stimulatory molecule was comparable in adult horse and foal macrophages and DCs, independent of treatment. CpG-ODN stimulation induced IL-12p40 (53 times) and IFNα (23 times) mRNA expression in CpG-ODN-treated adult horse DCs (p = 0.078), but not macrophages, in comparison to non-stimulated cells. In contrast, foal APCs did not respond to CpG-ODN stimulation with increased cytokine mRNA expression up to 3 months of age. TLR-9 mRNA expression and NF-kB activation (NF-kB p65) in foal DCs and macrophages were comparable (p > 0.05) to adult horse cells.

Conclusion

CpG-ODN treatment did not induce specific maturation and cytokine expression in foal macrophages and DCs. Nevertheless, adult horse DCs, but not macrophages, increased their expression of IL-12 and IFNα cytokines upon CpG-ODN stimulation. Importantly, foals presented an age-dependent limitation in the expression of MHC class II in macrophages and DCs, independent of treatment.

Contribution of T Cells and Neutrophils in Protection of Young Susceptible Rats from Fatal Experimental Malaria

In human malaria, children suffer very high rates of morbidity and mortality. To analyze the mechanisms involved in age-dependent protection against malaria, we developed an experimental model of infection in rats, where young rats are susceptible to Plasmodium berghei and adult rats control blood parasites and survive thereafter. In this study, we showed that protection of young rats could be achievable by adoptive transfer of spleen cells from adult protected rats, among which T cells could transfer partial protection. Transcriptome analysis of spleen cells transferring immunity revealed the overexpression of genes mainly expressed by eosinophils and neutrophils. Evaluation of the role of neutrophils showed that these cells were able to transfer partial protection to young rats. This antiparasitic effect was shown to be mediated, at least in part, through the neutrophil protein-1 defensin. Further adoptive transfer experiments indicated an efficient cooperation between neutrophils and T cells in protecting all young recipients. These observations, together with those from in vitro studies in human malaria, suggest that the failure of children to control infection could be related not only to an immaturity of their adaptive immunity but also to a lack in an adequate innate immune response.

An evaluation of the neonatal immune system using a listeria infection model

BACKGROUND

T helper 1 (Th1)/T helper 2 (Th2)-biased cytokine regulation may be another reason that neonates are much more susceptible to infectious disease than are adults.

OBJECTIVES

We attempted to determine the ability of neonatal mice to direct the Th1 phenotype against Listeria monocytogenes (LM), because LM, an intracellular Gram-positive bacterium, induces profound cellular immunity by Th1 cells in vivo.

METHODS

In order to determine whether neonatal mice evidence strong Th1 activity during LM infection, neonatal mice were compared with adult mice with regard to susceptibility to LM, cytotoxic T lymphocyte activity, and cytokine profiles. Neonatal gene profiles relevant to Th1 and Th2 differentiation during LM infection were also compared between neonatal and adult mice, via real-time PCR and RT-PCR.

RESULTS

Neonatal mice were found to be far more susceptible to LM infection than adult mice, due to a lack in the induction of cytotoxic T cell activity, coupled with poor IFN-gamma secretion. Further, LM-infected neonatal mice evidenced much lower levels of expression of Th1-type immune components, including IL-12, IFN-gamma, Delta-4 and T-bet, as compared to those features in adult mice. These results may be due to the comparably lower expressions of mannose-bind lectins and some of toll-like receptors (TLRs) such as TLR-5, -6 and -9, necessary mediators to develop Th1 immune responses.

CONCLUSIONS

Neonatal mice may not mount an adequate Th1 type immune response due to a significantly lower expression of Th1-type immune components as compared to adult mice, even when forced into a Th1-prone environment.

Innate immunity: toll-like receptors and some more. A brief history, basic organization and relevance for the human newborn

The discovery of Toll-like receptors (TLRs) as essential components of the innate immune system has greatly advanced our knowledge and understanding of immune responses to infection and how these are regulated. Innate immunity in general and TLRs in particular play a crucial role in the front line of host defenses against microbes, but also are a key element in the proper functioning of the immune system at large in vertebrate animals. The innate immune system has been identified as a collection of factors, both cell-associated and cell-free, that comprises an impressively effective and well-organized system that is capable of immediate recognition of a whole array of microbes and microbial components. The cell-bound TLRs fulfill a central role in the process from pathogen recognition to activation of adaptive immunity. From the cell-free factors the plasma protein mannose-binding lectin (MBL) has been studied most extensively. Associations have already been documented between TLR polymorphisms in man and TLR deficiency in animals and an increased susceptibility to infection. The effect of MBL on infectious disease susceptibility only seems to emerge when host defenses are compromised by a severe underlying condition. The functional state of the various components of innate immunity at birth is largely unknown and only recently a number of studies have assessed this feature of the innate immune system. In addition, for the human newborn the innate immune system may have a broader significance; it may well be the key system determining the course of inflammatory events associated with premature birth, a notion that is emphasized by the recently described association between TLR polymorphisms and prematurity. However, there are still many open questions, particularly about the exact relation between individual TLRs and infectious disease susceptibility and how TLRs cooperate in resistance to infection and in initiating adaptive immune responses. With regard to the human newborn, the most relevant question that needs to be resolved is the precise role of innate immunity in the pathogenesis of prematurity.

Prevalence of Toll-like receptor signalling defects in apparently healthy children who developed invasive pneumococcal infection

Human primary immunodeficiencies affecting Toll-like receptor (TLR) signalling reveal a non-redundant role for TLR function in defense against pneumococcal infection. To determine the clinical relevance of TLR abnormalities, we studied a population predicted to be enriched for TLR defects-healthy children who had developed invasive pneumococcal infection in the absence of classic risk factors for infection. We describe the development and optimization of a peripheral blood TLR assay. By testing 38 healthy control neonates, children and adults we demonstrated that TLR function was stable over the first six decades of life. We tested 50 children with a history of invasive pneumococcal infection and although TLR defects were predicted to be over-represented in this population, we did not identify any TLR abnormalities. Although TLR signalling defects are associated with greatly enhanced susceptibility to invasive pneumococcal infection, our results suggest that routine clinical screening for TLR defects in healthy children who develop invasive pneumococcal infection is not justified.

Interferon regulatory factor 3-dependent responses to lipopolysaccharide are selectively blunted in cord blood cells

The synthesis of interferon-β (IFNβ) and IFN-inducible factors elicited by lipopolysaccharide (LPS) depends on the transcriptional activity of interferon regulatory factor 3 (IRF-3) downstream of Toll-like receptor-4 (TLR4). To examine the ability of human newborns to mount TLR4-mediated IRF-3–dependent responses, we analyzed the pattern of genes expressed on the addition of LPS to cord blood or cord blood monocyte-derived dendritic cells (moDCs). Expression of IFNβ and IFN-inducible genes was selectively impaired in neonatal blood and moDCs as compared with their adult counterparts. This selective defect was confirmed by microarray experiments on moDCs. Altered expression of IFN-inducible genes was related to impaired IFNβ synthesis because IFNβ signaling was functional in neonatal moDCs. However, addition of exogenous IFNβ failed to restore LPS-induced IL-12p70 synthesis which was previously shown to be defective in neonatal moDCs. Although LPS-induced IRF-3 nuclear translocation was observed both in adult and neonatal moDCs, IRF-3 DNA-binding activity and association with the coactivator CREB-binding protein (CBP) were decreased in neonatal as compared with adult moDCs. We conclude that impaired IRF-3/CBP interaction in neonatal blood cells exposed to LPS is associated with impaired expression of IFNβ and IFN-inducible genes. Because IRF-3 activity is also required for IL-12p70 synthesis, our findings provide a molecular basis for the decreased ability of LPS-stimulated neonatal moDCs to elicit Th1-type responses.