Pregnancy-associated malaria affects toll-like receptor ligand-induced cytokine responses in cord blood

Correlates of malaria vaccine efficacy

Introduction: An effective vaccine against malaria forms a global health priority. Both naturally acquired immunity and sterile protection induced by irradiated sporozoite immunization were described decades ago. Still no vaccine exists that sufficiently protects children in endemic areas. Identifying immunological correlates of vaccine efficacy can inform rational vaccine design and potentially accelerate clinical development.Areas covered: We discuss recent research on immunological correlates of malaria vaccine efficacy, including: insights from state-of-the-art omics platforms and systems vaccinology analyses; functional anti-parasitic assays; pre-immunization predictors of vaccine efficacy; and comparison of correlates of vaccine efficacy against controlled human malaria infections (CHMI) and against naturally acquired infections.Expert Opinion: Effective vaccination may be achievable without necessarily understanding immunological correlates, but the relatively disappointing efficacy of malaria vaccine candidates in target populations is concerning. Hypothesis-generating omics and systems vaccinology analyses, alongside assessment of pre-immunization correlates, have the potential to bring about paradigm-shifts in malaria vaccinology. Functional assays may represent in vivo effector mechanisms, but have scarcely been formally assessed as correlates. Crucially, evidence is still meager that correlates of vaccine efficacy against CHMI correspond with those against naturally acquired infections in target populations. Finally, the diversity of immunological assays and efficacy endpoints across malaria vaccine trials remains a major confounder.

SEPSIS project: a protocol for studying biomarkers of neonatal sepsis and immune responses of infants in a malaria-endemic region

INTRODUCTION

Neonatal sepsis outreaches all causes of neonatal mortality worldwide and remains a major societal burden in low and middle income countries. In addition to limited resources, endemic morbidities, such as malaria and prematurity, predispose neonates and infants to invasive infection by altering neonatal immune response to pathogens. Nevertheless, thoughtful epidemiological, diagnostic and immunological evaluation of neonatal sepsis and the impact of gestational malaria have never been performed.

METHODS AND ANALYSIS

A prospective longitudinal multicentre follow-up of 580 infants from birth to 3 months of age in urban and suburban Benin will be performed. At delivery, and every other week, all children will be examined and clinically evaluated for occurrence of sepsis. At delivery, cord blood systematic analysis of selected plasma and transcriptomic biomarkers (procalcitonin, interleukin (IL)-6, IL-10, IP10, CD74 and CX3CR1) associated with sepsis pathophysiology will be evaluated in all live births as well as during the follow-up, and when sepsis will be suspected. In addition, whole blood response to selected innate stimuli and extensive peripheral blood mononuclear cells phenotypic characterisation will be performed. Reference intervals specific to sub-Saharan neonates will be determined from this cohort and biomarkers performances for neonatal sepsis diagnosis and prognosis tested.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Comité d'Ethique de la Recherche - Institut des Sciences Biomédicales Appliquées (CER-ISBA 85 - 5 April 2016, extended on 3 February 2017). Results will be disseminated through international presentations at scientific meetings and publications in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov registration number: NCT03780712.

Insight Into TLR4-Mediated Immunomodulation in Normal Pregnancy and Related Disorders

Unlike organ transplants where an immunosuppressive environment is required, a successful pregnancy involves an extremely robust, dynamic, and responsive maternal immune system to maintain the development of the fetus. A specific set of hormones and cytokines are associated with a particular stage of pregnancy. Any disturbance that alters this fine balance could compromise the development and function of the placenta. Although there are numerous underlying causes of pregnancy-related complications, untimely activation of Toll-like receptors (TLR), primarily TLR4, by intrauterine microbes poses the greatest risk. TLR4 is an important Pattern Recognition Receptor (PRR), which activates both innate and adaptive immune cells. TLR4 activation by LPS or DAMPs leads to the production of pro-inflammatory cytokines via the MyD88 dependent or independent pathway. Immune cells modulate the materno–fetal interface by TLR4-mediated cytokine production, which changes at different stages of pregnancy. In most pregnancy disorders, such as PTB, PE, or placental malaria, the TLR4 expression is upregulated in immune cells or in maternal derived cells, leading to the aberrant production of pro-inflammatory cytokines at the materno–fetal interface. Lack of functional TLR4 in mice has reduced the pro-inflammatory responses, leading to an improved pregnancy, which further strengthens the fact that abnormal TLR4 activation creates a hostile environment for the developing fetus. A recent study proposed that endothelial and perivascular stromal cells should interact with each other in order to maintain a homeostatic balance during TLR4-mediated inflammation. It has been reported that depleting immune cells or supplying anti-inflammatory cytokines can prevent PTB, PE, or fetal death. Blocking TLR4 signaling or its downstream molecule by inhibitors or antagonists has proven to improve pregnancy-related complications to some extent in clinical and animal models. To date, there has been a lack of knowledge regarding whether TLR4 accessories such as CD14 and MD-2 are important in pregnancy and whether these accessory molecules could be promising drug targets for combinatorial treatment of various pregnancy disorders. This review mainly focuses on the activation of TLR4 during pregnancy, its immunomodulatory functions, and the upcoming advancement in this field regarding the improvement of pregnancy-related issues by various therapeutic approaches.

Fetal-Derived MyD88 Signaling Contributes to Poor Pregnancy Outcomes During Gestational Malaria

Placental malaria (PM) remains a severe public health problem in areas of high malaria transmission. Despite the efforts to prevent infection poor outcomes in Plasmodium endemic areas, there is still a considerable number of preterm births and newborns with low birth weight resulting from PM. Although local inflammation triggered in response to malaria is considered crucial in inducing placental damage, little is known about the differential influence of maternal and fetal immune responses to the disease progression. Therefore, using a PM mouse model, we sought to determine the contribution of maternal and fetal innate immune responses to PM development. For this, we conducted a series of cross-breeding experiments between mice that had differential expression of the MyD88 adaptor protein to obtain mother and correspondent fetuses with distinct genetic backgrounds. By evaluating fetal weight and placental vascular spaces, we have shown that the expression of MyD88 in fetal tissue has a significant impact on PM outcomes. Our results highlighted the existence of a distinct contribution of maternal and fetal immune responses to PM onset. Thus, contributing to the understanding of how inflammatory processes lead to the dysregulation of placental homeostasis ultimately impairing fetal development.

Submicroscopic Plasmodium infection during pregnancy is associated with reduced antibody levels to tetanus toxoid

Submicroscopic Plasmodium infections in pregnancy are common in endemic areas, and it is important to understand the impact of these low-level infections. Asymptomatic, chronic infections are advantageous for parasite persistence, particularly in areas where the optimal eco-epidemiological conditions for parasite transmission fluctuate. In chronic infections, the persistence of the antigenic stimulus changes the expression of immune mediators and promotes constant immune regulation, including increases in regulatory T cell populations. These alterations of the immune system could compromise the response to routine vaccination. This study aimed to evaluate the effect of submicroscopic plasmodial infection with P. falciparum and P. vivax during pregnancy on the immune response to the tetanus toxoid vaccine in Colombian women. Expression of different cytokines and mediators of immune regulation and levels of anti-tetanus toxoid (TT) immunoglobulin (Ig)G were quantified in pregnant women with and without submicroscopic plasmodial infection. The anti-TT IgG levels were significantly lower in the infected group compared with the uninfected group. The expression of interferon (IFN)-γ, tumour necrosis factor (TNF) and forkhead box protein 3 (FoxP3) was significantly higher in the infected group, while the expression of cytotoxic T lymphocyte antigen 4 (CTLA-4) and transforming growth factor (TGF)-β was lower in the group of infected. In conclusion, submicroscopic Plasmodium infection altered the development of the immune response to the TT vaccine in Colombian pregnant women. The impact of Plasmodium infections on the immune regulatory pathways warrants further exploration.

How does malaria in pregnancy impact malaria risk in infants?

Malaria in pregnancy not only exerts profound negative consequences on the health of the mother and developing fetus, but may also alter the risk of malaria during infancy. Although mechanisms driving this altered risk remain unclear, in utero exposure to malaria antigens may impact the development of fetal and infant innate immunity. In an article in BMC Medicine, Natama et al. describe an ambitious analysis of basal and TLR-stimulated cord blood responses among a birth cohort in Burkina Faso. Basal levels of several cytokines, chemokines, and growth factors were shown to be significantly lower in cord blood with histopathologic evidence of placental malaria. Additionally, following TLR7/8 stimulation, samples obtained from infants of mothers with placental malaria were hyper-responsive compared to those without evidence of prenatal malaria exposure. Furthermore, several responses impacted by placental malaria were associated with differential malaria risk in infancy. Understanding how malaria in pregnancy shapes immune responses in infants will provide critical insight into the rational design of malaria control strategies during pregnancy, including intermittent preventative treatment in pregnancy and vaccines.Please see related article: https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-018-1187-3.

Modulation of innate immune responses at birth by prenatal malaria exposure and association with malaria risk during the first year of life

BACKGROUND

Factors driving inter-individual differences in immune responses upon different types of prenatal malaria exposure (PME) and subsequent risk of malaria in infancy remain poorly understood. In this study, we examined the impact of four types of PME (i.e., maternal peripheral infection and placental acute, chronic, and past infections) on both spontaneous and toll-like receptors (TLRs)-mediated cytokine production in cord blood and how these innate immune responses modulate the risk of malaria during the first year of life.

METHODS

We conducted a birth cohort study of 313 mother-child pairs nested within the COSMIC clinical trial (NCT01941264), which was assessing malaria preventive interventions during pregnancy in Burkina Faso. Malaria infections during pregnancy and infants' clinical malaria episodes detected during the first year of life were recorded. Supernatant concentrations of 30 cytokines, chemokines, and growth factors induced by stimulation of cord blood with agonists of TLRs 3, 7/8, and 9 were measured by quantitative suspension array technology. Crude concentrations and ratios of TLR-mediated cytokine responses relative to background control were analyzed.

RESULTS

Spontaneous production of innate immune biomarkers was significantly reduced in cord blood of infants exposed to malaria, with variation among PME groups, as compared to those from the non-exposed control group. However, following TLR7/8 stimulation, which showed higher induction of cytokines/chemokines/growth factors than TLRs 3 and 9, cord blood cells of infants with evidence of past placental malaria were hyper-responsive in comparison to those of infants not-exposed. In addition, certain biomarkers, which levels were significantly modified depending on the PME category, were independent predictors of either malaria risk (GM-CSF TLR7/8 crude) or protection (IL-12 TLR7/8 ratio and IP-10 TLR3 crude, IL-1RA TLR7/8 ratio) during the first year of life.

CONCLUSIONS

These findings indicate that past placental malaria has a profound effect on fetal immune system and that the differential alterations of innate immune responses by PME categories might drive heterogeneity between individuals to clinical malaria susceptibility during the first year of life.

Transplacental immune modulation with a bacterial-derived agent protects against allergic airway inflammation

Chronic allergic inflammatory diseases are a major cause of morbidity, with allergic asthma alone affecting over 300 million people worldwide. Epidemiological studies demonstrate that environmental stimuli are associated with either the promotion or prevention of disease. Major reductions in asthma prevalence are documented in European and US farming communities. Protection is associated with exposure of mothers during pregnancy to microbial breakdown products present in farm dusts and unprocessed foods and enhancement of innate immune competence in the children. We sought to develop a scientific rationale for progressing these findings toward clinical application for primary disease prevention. Treatment of pregnant mice with a defined, clinically approved immune modulator was shown to markedly reduce susceptibility of their offspring to development of the hallmark clinical features of allergic airway inflammatory disease. Mechanistically, offspring displayed enhanced dendritic cell-dependent airway mucosal immune surveillance function, which resulted in more efficient generation of mucosal-homing regulatory T cells in response to local inflammatory challenge. We provide evidence that the principal target for maternal treatment effects was the fetal dendritic cell progenitor compartment, equipping the offspring for accelerated functional maturation of the airway mucosal dendritic cell network following birth. These data provide proof of concept supporting the rationale for developing transplacental immune reprogramming approaches for primary disease prevention.

Correlating efficacy and immunogenicity in malaria vaccine trials

The availability of an effective and appropriately implemented malaria vaccine would form a crucial cornerstone of public health efforts to fight this disease. Despite many decades of research, however, no malaria vaccine has yet shown satisfactory protective efficacy or been rolled-out. Validated immunological substitute endpoints have the potential to accelerate clinical vaccine development by reducing the required complexity, size, duration and cost of clinical trials. Besides facilitating clinical development of existing vaccine candidates, understanding immunological mechanisms of protection may drive the development of fundamentally new vaccination approaches. In this review we focus on correlates of protection in malaria vaccine development: Does immunogenicity predict malaria vaccine efficacy and why is this question particularly difficult? Have immunological correlates accelerated malaria vaccine development in the past and will they facilitate it in the future? Does Controlled Human Malaria Infection represent a valid model for identifying such immunological correlates, or a correlate of protection against naturally-acquired malaria in itself?

Malaria in pregnancy shapes the development of foetal and infant immunity

Malaria, particularly Plasmodium falciparum, continues to disproportionately affect pregnant women. In addition to the profoundly deleterious impact of maternal malaria on the health of the mother and foetus, malaria infection in pregnancy has been shown to affect the development of the foetal and infant immune system and may alter the risk of malaria and nonmalarial outcomes during infancy. This review summarizes our current understanding of how malaria infection in pregnancy shapes the protective components of the maternal immune system transferred to the foetus and how foetal exposure to parasite antigens impacts the development of foetal and infant immunity. It also reviews existing evidence linking malaria infection in pregnancy to malaria and nonmalarial outcomes in infancy and how preventing malaria in pregnancy may alter these outcomes. A better understanding of the consequences of malaria infection in pregnancy on the development of foetal and infant immunity will inform control strategies, including intermittent preventive treatment in pregnancy and vaccine development.

High production of pro-inflammatory cytokines by maternal blood mononuclear cells is associated with reduced maternal malaria but increased cord blood infection

Background

Increased susceptibility to malaria during pregnancy is not completely understood. Cellular immune responses mediate both pathology and immunity but the effector responses involved in these processes have not been fully characterized. Maternal and fetal cytokine and chemokine responses to malaria at delivery, and their association with pregnancy and childhood outcomes, were investigated in 174 samples from a mother and child cohort from Mozambique. Peripheral and cord mononuclear cells were stimulated with Plasmodium falciparum lysate and secretion of IL-12p70, IFN-γ, IL-2, IL-10, IL-8, IL-6, IL-4, IL-5, IL-1β, TNF, TNF-β was quantified in culture supernatants by multiplex flow cytometry while cellular mRNA expression of IFN-γ, TNF, IL-2, IL-4, IL-6, IL-10 and IL-13 was measured by quantitative PCR.

Results

Higher concentrations of IL-6 and IL-1β were associated with a reduced risk of P. falciparum infection in pregnant women (p < 0.049). Pro-inflammatory cytokines IL-6, IL-1β and TNF strongly correlated among themselves (ρ > 0.5, p < 0.001). Higher production of IL-1β was significantly associated with congenital malaria (p < 0.046) and excessive TNF was associated with peripheral infection and placental lesions (p < 0.044).

Conclusions

Complex network of immuno-pathological cytokine mechanisms in the placental and utero environments showed a potential trade-off between positive and negative effects on mother and newborn susceptibility to infection.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2317-2) contains supplementary material, which is available to authorized users.

Malaria incidence and prevalence during the first year of life in Nanoro, Burkina Faso: a birth-cohort study

Background

Infants are thought to be protected against malaria during the first months of life mainly due to passage of maternal antibodies. However, in high transmission settings, malaria in early infancy is not uncommon and susceptibility to the infections varies between individuals. This study aimed to determine malaria morbidity and infection during early childhood in rural Burkina Faso.

Methods

Malariometric indices were determined over 1-year follow-up in a birth cohort of 734 infants living in Nanoro health district. Clinical malaria episodes were determined by passive case detection at peripheral health centres while asymptomatic malaria infections were identified during  4 cross-sectional surveys at 3, 6, 9 and 12 months of age. Plasmodium falciparum infections were detected by rapid diagnostic test and/or light microscopy (LM) and quantitative PCR (qPCR).

Results

In total, 717 clinical episodes were diagnosed by qPCR over 8335.18 person-months at risk. The overall malaria incidence was 1.03 per child-year and increased from 0.27 per child-year at 0–3 months of age to 1.92 per child-year at 9–12 months of age. Some 59% of children experienced at least one clinical episode with a median survival time estimated at 9.9 months, while 20% of infants experienced the first episode before 6 months of age. The majority of the clinical episodes were attributable to microscopic parasitaemia (84.2%), and there was a positive correlation between parasite density and age (Spearman’s rho = 0.30; P < 0.0001). Prevalence of asymptomatic infections was similar at 3, 6 and 9 months of age (17.7–20.1%) and nearly 1.6 times higher at 12 months (31.3%). Importantly, gametocyte prevalence among the LM-positive study population was 6.7%, but increased to 10% among asymptomatic infections. In addition, 46% of asymptomatic infections were only detected by qPCR suggesting that infants below 1 year are a potential reservoir for sustaining malaria transmission. Both symptomatic and asymptomatic infections showed marked seasonal distribution with the highest transmission period (July to December) accounting for about 89 and 77% of those infections, respectively.

Conclusions

These findings indicate high and marked age and seasonal-dependency of malaria infections and disease during the first year of life in Nanoro, calling for intensified efforts to control malaria in rural Burkina Faso.

A Malaria-Resistant Phenotype with Immunological Correlates in a Tanzanian Birth Cohort Exposed to Intense Malaria Transmission

AbstractMalaria incidence is highly heterogeneous even in areas of high transmission, although no conclusive evidence exists that innate or naturally acquired resistance can prevent infection over an extended period of time. This longitudinal study examined immunoparasitological evidence for a malaria-resistant phenotype in which children do not develop malaria despite an extended period of exposure to parasites. Within a birth cohort followed from 2002 to 2006 in Muheza, Tanzania, an area of intense transmission, children (N = 687) provided blood smears biweekly during infancy and monthly thereafter. Maternal and childhood characteristics were obtained, cord-blood cytokines were measured, and antibody responses were assayed as measures of stage-specific exposure. Sixty-three (9.2%) children had no blood smear-positive slides over 2 years of follow-up (range: 1-3.5 years) and were identified as malaria resistant. Malaria-resistant children were similar to other children with respect to completeness of follow-up and all maternal and childhood characteristics except residence area. Antibody seroprevalence was similar for two sporozoite antigens, but malaria-resistant children had a lower antibody seroprevalence to merozoite antigens merozoite surface protein 1 (5.4% versus 30.2%; P < 0.0001) and apical membrane antigen 1 (7.2% versus 33.3%; P < 0.0001). Malaria-resistant children had higher cytokine levels in cord blood, particularly interleukin-1β. In summary, a subset of children living in an area of intense transmission was exposed to malaria parasites, but never developed patent parasitemia; this phenotype was associated with a distinct cytokine profile at birth and antibody profile during infancy. Further research with malaria-resistant children may identify mechanisms for naturally acquired immunity.

Plasmodium falciparum infection is associated with Epstein-Barr virus reactivation in pregnant women living in malaria holoendemic area of Western Kenya

The role of Plasmodium falciparum malaria in Epstein-Barr virus (EBV) transmission among infants early in life remain elusive. We hypothesized that infection with malaria during pregnancy could cause EBV reactivation leading to high EBV load in circulation, which could subsequently enhance early age of EBV infection. Pregnant women in Kisumu, where P. falciparum malaria is holoendemic, were actively followed monthly through antenatal visits (up to 4 per mother) and delivery. Using real-time quantitative (Q)-PCR, we quantified and compared EBV and P. falciparum DNA levels in the blood of pregnant women with and without P. falciparum malaria. Pregnant women that had malaria detected during pregnancy were more likely to have detectable EBV DNA than pregnant women who had no evidence of malaria infection during pregnancy (64 vs. 36 %, p = 0.01). EBV load as analyzed by quantifying area under the longitudinal observation curve (AUC) was significantly higher in pregnant women with P. falciparum malaria than in women without evidence of malaria infection (p = 0.01) regardless of gestational age of pregnancy. Increase in malaria load correlated with increase in EBV load (p < 0.0001). EBV load was higher in third trimester (p = 0.04) than first and second trimester of pregnancy independent of known infections. Significantly higher frequency and elevated EBV loads were found in pregnant women with malaria than in women without evidence of P. falciparum infection during pregnancy. The loss of control of EBV latency following P. falciparum infection during pregnancy and subsequent increase in EBV load in circulation could contribute to enhanced shedding of EBV in maternal saliva and breast milk postpartum, but further studies are needed.

Infants' Peripheral Blood Lymphocyte Composition Reflects Both Maternal and Post-Natal Infection with Plasmodium falciparum

Maternal parasitoses modulate fetal immune development, manifesting as altered cellular immunological activity in cord blood that may be linked to enhanced susceptibility to infections in early life. Plasmodium falciparum typifies such infections, with distinct placental infection-related changes in cord blood exemplified by expanded populations of parasite antigen-specific regulatory T cells. Here we addressed whether such early-onset cellular immunological alterations persist through infancy. Specifically, in order to assess the potential impacts of P. falciparum infections either during pregnancy or during infancy, we quantified lymphocyte subsets in cord blood and in infants' peripheral blood during the first year of life. The principal age-related changes observed, independent of infection status, concerned decreases in the frequencies of CD4⁺, NK^dim and NKT cells, whilst CD8⁺, Treg and Teff cells' frequencies increased from birth to 12 months of age. P. falciparum infections present at delivery, but not those earlier in gestation, were associated with increased frequencies of Treg and CD8⁺ T cells but fewer CD4⁺ and NKT cells during infancy, thus accentuating the observed age-related patterns. Overall, P. falciparum infections arising during infancy were associated with a reversal of the trends associated with maternal infection i.e. with more CD4⁺ cells, with fewer Treg and CD8⁺ cells. We conclude that maternal P. falciparum infection at delivery has significant and, in some cases, year-long effects on the composition of infants' peripheral blood lymphocyte populations. Those effects are superimposed on separate and independent age- as well as infant infection-related alterations that, respectively, either match or run counter to them.

The impact of HIV exposure and maternal Mycobacterium tuberculosis infection on infant immune responses to bacille Calmette-Guérin vaccination

Objective:

The objective of this study is to assess the effect of maternal HIV and Mycobacterium tuberculosis (Mtb) infection on cellular responses to bacille Calmette-Guérin (BCG) immunization.

Design:

A mother–infant cohort study.

Methods:

Samples were collected from mother–infant pairs at delivery. Infants were BCG-vaccinated at 6 weeks of age and a repeat blood sample was collected from infants at 16 weeks of age. BCG-specific T-cell proliferation and intracellular cytokine expression were measured by flow cytometry. Secreted cytokines and chemokines in cell culture supernatants were analysed using a Multiplex assay.

Results:

One hundred and nine (47 HIV-exposed and 62 HIV-unexposed) mother–infants pairs were recruited after delivery and followed longitudinally. At birth, proportions of mycobacteria-specific proliferating T cells were not associated with either in-utero HIV exposure or maternal Mtb sensitization. However, in-utero HIV exposure affected infant-specific T-cell subsets [tumour necrosis factor-alpha (TNF-α) single positive proliferating CD4⁺ T cells and interferon-gamma (IFN-γ), TNF-α dual-positive CD4⁺ T cells]. Levels of TNF-α protein in cell culture supernatants were also significantly higher in HIV-exposed infants born to Mtb-sensitized mothers. In the presence of maternal Mtb sensitization, frequencies of maternal and newborn BCG-specific proliferating CD4⁺ T cells were positively correlated. Following BCG vaccination, there was no demonstrable effect of HIV exposure or maternal Mtb infection on infant BCG-specific T-cell proliferative responses or concentrations of secreted cytokines and chemokines.

Conclusion:

Effects of maternal HIV and Mtb infection on infant immune profiles at birth are transient only, and HIV-exposed, noninfected infants have the same potential to respond to and be protected by BCG vaccination as HIV-unexposed infants.

CD4+CD25hiFOXP3+ cells in cord blood of neonates born from filaria infected mother are negatively associated with CD4+Tbet+ and CD4+RORγt+ T cells

Background

Children who have been exposed in utero to maternal filarial infection are immunologically less responsive to filarial antigens, have less pathology, and are more susceptible to acquire infection than offspring of uninfected mothers. Moreover children from filaria infected mothers have been shown to be less responsive to vaccination as a consequence of an impairment of their immune response. However, it is not well known how in utero exposure to parasite antigens affects cellular immune responses.

Methodology

Here, 30 pregnant women were examined for the presence of microfilaria of Loa loa and Mansonella perstans in peripheral blood. At delivery, cord blood mononuclear cells (CBMC) were obtained and the CD4⁺T cells were phenotyped by expression of the transcription factors Tbet, RORγt, and FOXP3.

Results

No significant difference was observed between newborns from infected versus uninfected mothers in the frequencies of total CD4⁺T cells and CD4⁺T cells subsets including CD4⁺Tbet⁺, CD4⁺RORγt⁺ T and CD4⁺CD25^hiFOXP3⁺ T cells. However, there was a negative association between CD4⁺CD25^hiFOXP3⁺T cells and CD4⁺Tbet⁺ as well as CD4⁺RORγt⁺ T cells in the infected group only (B = −0.242, P = 0.002; B = −0.178, P = 0.013 respectively).

Conclusion

Our results suggest that filarial infection during pregnancy leads to an expansion of functionally active regulatory T cells that keep TH1 and TH17 in check.

Fetal origins of malarial disease: cord blood cytokines as risk markers for pediatric severe malarial anemia

BACKGROUND

Severe malarial anemia (SMA) remains a major cause of pediatric illness and mortality in Sub-Saharan Africa. Here we test the hypothesis that prenatal exposures, reflected by soluble inflammatory mediators in cord blood, can condition an individual's susceptibility to SMA.

METHODS

In a Tanzanian birth cohort (n = 743), we measured cord blood concentrations of tumor necrosis factor (TNF), TNF receptors I and II (TNF-RI and TNF-RII), interleukin (IL)-1β, IL-4, IL-5, IL-6, IL-10, and interferon gamma (IFN-γ). After adjusting for conventional covariates, we calculated the hazard ratios (HR) for time to first SMA event with log(e) cytokine concentrations dichotomized at the median, by quartile, and per standard deviation (SD) increase.

RESULTS

Low levels of TNF, TNF-RI, IL-1β, and IL-5 and high levels of TNF-RII were associated statistically significantly and respectively with approximately 3-fold, 2-fold, 8-fold, 4-fold, and 3-fold increased risks of SMA (Hb < 50 g/L). TNF, TNF-RI, and IL-1β concentrations were inversely and log-linearly associated with SMA risk; the HR (95% confidence interval [CI]) per 1-SD increase were respectively 0.81 (.65, 1.02), 0.76 (.62, .92), and 0.50 (.40, .62).

CONCLUSIONS

These data suggest that proinflammatory cytokine levels at birth are inversely associated with SMA risk and support the hypothesis that pediatric malarial disease has fetal origins.

Maturation of innate responses to mycobacteria over the first nine months of life

Newborns and young infants are particularly susceptible to infections, including Mycobacterium tuberculosis. Further, immunogenicity of vaccines against tuberculosis and other infectious diseases appears suboptimal early in life compared with later in life. We hypothesized that developmental changes in innate immunity would underlie these observations. To determine the evolution of innate responses to mycobacteria early in life, whole blood or PBMC from newborns, as well as 10- and 36-wk-old infants, was incubated with viable Mycobacterium bovis bacillus Calmette-Guérin or TLR ligands. Innate cell expression of cytokines and maturation markers was assessed, as well as activation of the proinflammatory NF-κB- and MAPK-signaling pathways. Bacillus Calmette-Guérin-induced production of the proinflammatory cytokines TNF-α, IL-6, and IL-12p40 increased from the newborn period to 9 mo of age in monocytes but not in myeloid dendritic cells. No changes in production of anti-inflammatory IL-10 were observed. CD40 expression increased with age in both cell populations. Older infants displayed substantial activation of all three signal transduction molecules: degradation of NF-κB inhibitor IκBα and phosphorylation of MAPK Erk and p38 upon TLR1/2 triggering, compared with predominant activation of only one of any of these molecules in newborns. Maturation of innate proinflammatory responses during the first 9 mo of life may underlie more effective control of mycobacteria and other pathogens observed later in infancy and age-related differential induction of Th1 responses by vaccination.

Cord blood Vγ2Vδ2 T cells provide a molecular marker for the influence of pregnancy-associated malaria on neonatal immunity

BACKGROUND

Plasmodium falciparum placental infection primes the fetal immune system and alters infant immunity. Mechanisms leading to these outcomes are not completely understood. We focused on Vγ2Vδ2 cells, which are part of the immune response against many pathogens, including P. falciparum. These unconventional lymphocytes respond directly to small, nonpeptidic antigens, independent of major histocompatibility complex presentation. We wondered whether placental malaria, which may increase fetal exposure to P. falciparum metabolites, triggers a response by neonatal Vγ2Vδ2 lymphocytes that can be a marker for the extent of fetal exposure to malarial antigens.

METHODS

Cord blood mononuclear cells were collected from 15 neonates born to mothers with P. falciparum infection during pregnancy (8 with placental malaria) and 25 unexposed neonates. Vγ2Vδ2 cell phenotype, repertoire, and proliferative responses were compared between newborns exposed and those unexposed to P. falciparum.

RESULTS

Placental malaria-exposed neonates had increased proportions of central memory Vγ2Vδ2 cells in cord blood, with an altered Vγ2 chain repertoire ex vivo and after stimulation.

CONCLUSION

Our results suggest that placental malaria affects the phenotype and repertoire of neonatal Vγ2Vδ2 lymphocytes. Placental malaria may lower the capacity for subsequent Vγ2Vδ2 cell responses and impair the natural resistance to infectious diseases or the response to pediatric vaccination.

Malaria diagnostics in clinical trials

Malaria diagnostics are widely used in epidemiologic studies to investigate natural history of disease and in drug and vaccine clinical trials to exclude participants or evaluate efficacy. The Malaria Laboratory Network (MLN), managed by the Office of HIV/AIDS Network Coordination, is an international working group with mutual interests in malaria disease and diagnosis and in human immunodeficiency virus/acquired immunodeficiency syndrome clinical trials. The MLN considered and studied the wide array of available malaria diagnostic tests for their suitability for screening trial participants and/or obtaining study endpoints for malaria clinical trials, including studies of HIV/malaria co-infection and other malaria natural history studies. The MLN provides recommendations on microscopy, rapid diagnostic tests, serologic tests, and molecular assays to guide selection of the most appropriate test(s) for specific research objectives. In addition, this report provides recommendations regarding quality management to ensure reproducibility across sites in clinical trials. Performance evaluation, quality control, and external quality assessment are critical processes that must be implemented in all clinical trials using malaria tests.

Malaria modifies neonatal and early-life toll-like receptor cytokine responses

Protection from infections in early life relies extensively on innate immunity, but it is unknown whether and how maternal infections modulate infants' innate immune responses, thereby altering susceptibility to infections. Plasmodium falciparum causes pregnancy-associated malaria (PAM), and epidemiological studies have shown that PAM enhances infants' susceptibility to infection with P. falciparum. We investigated how PAM-mediated exposures in utero affect innate immune responses and their relationship with infection in infancy. In a prospective study of mothers and their babies in Benin, we investigated changes in Toll-like receptor (TLR)-mediated cytokine responses related to P. falciparum infections. Whole-blood samples from 134 infants at birth and at 3, 6, and 12 months of age were stimulated with agonists specific for TLR3, TLR4, TLR7/8, and TLR9. TLR-mediated interleukin 6 (IL-6) and IL-10 production was robust at birth and then stabilized, whereas tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ) responses were weak at birth and then increased. In multivariate analyses, maternal P. falciparum infections at delivery were associated with significantly higher TLR3-mediated IL-6 and IL-10 responses in the first 3 months of life (P < 0.05) and with significantly higher TLR3-, TLR7/8-, and TLR9-mediated TNF-α responses between 6 and 12 months of age (P < 0.05). Prospective analyses showed that higher TLR3- and TLR7/8-mediated IL-10 responses at birth were associated with a significantly higher risk of P. falciparum infection in infancy (P < 0.05). Neonatal and infant intracellular TLR-mediated cytokine responses are conditioned by in utero exposure through PAM late in pregnancy. Enhanced TLR-mediated IL-10 responses at birth are associated with an increased risk of P. falciparum infection, suggesting a compromised ability to combat infection in early life.

Variation between Populations in the Innate Immune Response to Vaccine Adjuvants

The success of the World Health Organization recommended “Expanded Program of Immunization” (EPI) and similar regional or national programs has been astounding. However, infectious threats currently not covered by these programs continue to infect millions of infants around the world. Furthermore, many infants do not receive existing vaccines either on time or for the required number of doses to provide optimal protection. Nor do all infants around the world develop the same protective immune response to the same vaccine. As a result approximately three million infants die every year from vaccine preventable infections. To tackle these issues, new vaccines need to be developed as well as existing ones made easier to administer. This requires identification of age-optimized vaccine schedules and formulations. In order to be most effective this approach will need to take population-based differences in response to vaccines and adjuvants into account. This review summarizes what is currently known about differences between populations around the world in the innate immune response to existing as well as new and promising vaccine adjuvants.

Do multiple concurrent infections in African children cause irreversible immunological damage?

Much of the developing world, particularly sub-Saharan Africa, has high levels of morbidity and mortality associated with infectious diseases. The greatest risk of invasive disease is in the young, the malnourished and HIV-infected individuals. In many regions in Africa these vulnerable groups and the wider general population are under constant immune pressure from a range of environmental factors, under-nutrition and multiple concurrent infections from birth through to adulthood. Intermittent microbial exposure during childhood is required for the generation of naturally acquired immunity capable of protection against a range of infectious diseases in adult life. However, in the context of a resource-poor setting, the heavy burden of malarial, diarrhoeal and respiratory infections in childhood may subvert or suppress immune responses rather than protect, resulting in sub-optimal immunity. This review will explore how poor maternal health, HIV exposure, socio-economic and seasonal factors conspire to weaken childhood immune defences to disease and discuss the hypothesis that recurrent infections may drive immune dysregulation, leading to relative immune senescence and premature immunological aging.

Uninfected but not unaffected: chronic maternal infections during pregnancy, fetal immunity, and susceptibility to postnatal infections

Chronic infections during pregnancy are highly prevalent in some parts of the world. Infections with helminths, Trypanosoma cruzi, Plasmodium spp, and HIV might affect the development of fetal immunity and susceptibility to postnatal infections independently of in-utero transmission of the pathogens. Fetal adaptive immune responses are common in neonates who have been exposed to maternal infection during pregnancy but not infected themselves. Such responses could affect the development of immunity to the homologous pathogens and their control during the first few years of life. Fetal innate and regulatory responses might also affect immunity to unrelated pathogens and responses to vaccines. Strategies to improve child health should integrate the possible clinical implications of in-utero exposure to chronic maternal infections.

Placental malaria-associated suppression of parasite-specific immune response in neonates has no major impact on systemic CD4 T cell homeostasis

In areas where Plasmodium falciparum is endemic, pregnancy is associated with accumulation of infected red blood cells (RBCs) in the placenta, a condition referred to as placental malaria (PM). Infants born to PM-positive mothers are at an increased risk of malaria, which is putatively related to the transplacental passage of parasite-derived antigens, with consequent tolerization of the fetal immune system. Here we addressed the impact of PM on the regulation of neonatal T cell responses. We found that the frequency of regulatory CD25(+) CD127(-/low) Foxp3(+) CD4(+) T cells was significantly decreased in neonates born to mothers with high levels of P. falciparum-induced placental inflammation, consisting mainly of primigravid mothers. However, at the individual level, the ratio between regulatory and effector (CD25(+) CD127(+) Foxp3(-)) CD4(+) T cells was unaffected by PM. In addition, parasite-induced CD4(+) T cell activation and production of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and IL-10 were strongly reduced in neonates born to PM-positive mothers. Thus, our results show that active PM at delivery is associated with a marked suppression of P. falciparum-specific cellular neonatal immune responses, affecting secretion of both pro- and anti-inflammatory cytokines. Additionally, our results suggest that, as in adults, effector and regulatory CD4(+) T cell populations are tightly coregulated in all neonates, irrespective of the maternal infection status.

Neonatal immune function and inflammatory illnesses in later life: lessons to be learnt from the developing world?

With the emergence of allergic and autoimmune diseases in populations that have started to transit to a western lifestyle, there has been an increasing interest in the role of environmental factors modulating early immune function. Yet, most of the information concerning neonatal immune function has been derived from studies in westernized countries. We postulate that comparative studies of early immune development in children born under conditions that are typical for a westernized vs. that of a still more traditional setting will provide a crucial insight into the environmental-driven immunological mechanisms that are responsible for the world-wide rise in inflammatory disorders. In this review, we summarize the current understanding of early-life immune function in humans in general and the literature on some major lifestyle factors that may influence neonatal immune function and potentially the risk for disease in later life. An understanding of the mechanisms of 'prenatal/early-life programming' in populations living in traditional compared with modern societies is crucial to develop strategies to prevent a further rise in 'western diseases' such as allergic disorders. Indications exist that prenatal conditioning of the innate immune system by low-grade inflammatory responses is key to inducing more tightly regulated postnatal adaptive immune responses.

Interferon-γ--central mediator of protective immune responses against the pre-erythrocytic and blood stage of malaria

Immune responses against Plasmodium parasites, the causative organisms of malaria, are traditionally dichotomized into pre-erythrocytic and blood-stage components. Whereas the central role of cellular responses in pre-erythrocytic immunity is well established, protection against blood-stage parasites has generally been ascribed to humoral responses. A number of recent studies, however, have highlighted the existence of cellular immunity against blood-stage parasites, in particular, the prominence of IFN-γ production. Here, we have undertaken to chart the contribution of this prototypical cellular cytokine to immunity against pre-erythrocytic and blood-stage parasites. We summarize the various antiparasitic effector functions that IFN-γ serves to induce, review an array of data about its protective effects, and scrutinize evidence for any deleterious, immunopathological outcome in malaria patients. We discuss the activation and contribution of different cellular sources of IFN-γ production during malaria infection and its regulation in relation to exposure. We conclude that IFN-γ forms a central mediator of protective immune responses against pre-erythrocytic and blood-stage malaria parasites and identify a number of implications for rational malaria vaccine development.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: neonatal immune function and vaccine responses in children born in low-income versus high-income countries

There is increasing evidence that the functional state of the immune system at birth is predictive of the kinetics of immune maturation in early infancy. Moreover, this maturation process can have a major impact on early vaccine responses and can be a key determinant of risk for communicable and non-communicable diseases in later life. We hypothesize that environmental and genetic factors that are often typical for poor-resource countries may have an important impact on prenatal immune development and predispose populations in low-income settings to different vaccine responses and disease risks, compared to those living in high-income countries. In this paper we aimed to summarize the major differences between neonatal and adult immune function and describe what is known so far about discrepancies in immune function between newborns in high- and low-income settings. Further, we discuss the need to test the immunological feasibility of accelerated vaccination schedules in high-risk populations and the potential of variation in disease specific and non-specific vaccine effects.

Determinants of the relationship between cytokine production in pregnant women and their infants

Exposure to environmental factors during fetal life and infancy is thought to play an important role in the early development of innate and adaptive immunity. The immunological relationship between mother and infant and the effect that environmental exposures have during pregnancy and early childhood have not been studied extensively. Here the production of cytokines was measured in 146 pairs of mothers and their 2- month-old infants. The effect of place of residence, socio-economic variables, parasitic infections as well as maternal and child characteristics on measured cytokine production was determined. Mothers producing high levels of IL-10, IFN-gamma and IL-5 were more likely to have infants who also produced high levels of these cytokines either spontaneously (OR 2.6(95%CI 1.2-5.4), OR 2.9(CI 1.3-6.6), OR 11.2(CI 4.6-27.2), respectively) or in response to PHA (IL-10: OR 3.0(CI 1.4-6.6), IFN-gamma: OR 2.0(CI 1.0-4.2), respectively) even after adjustment for potential confounding variables. This was not the case for TNF-alpha. In response to LPS, place of residence was a strong determinant of infant IL-10 (OR 0.2(CI 0.1-0.9)) and TNF-alpha (OR 0.3(CI 0.1-0.9)) production. Maternal protozoan infections was independently associated with reduced infant IL10 in response to PHA and to LPS as well as reduced TNF-alpha and IFN-gamma in response to PHA. These results indicate strong relationship between maternal and infant's cellular immune responses even after taking into account many environmental influences that could affect infant's response directly or indirectly through uterine microenvironment. However, place of residence and intestinal infections may still directly affect the immune responses of the infant. Taken together, the study provides evidence for imprinted cytokine responses of an infant which may have implications for their reaction to incoming antigens, warranting further investigation into the role that genetics or epigenetics play in shaping the cytokine response by an infant to self or external antigens.

Plasmodium falciparum exposure in utero, maternal age and parity influence the innate activation of foetal antigen presenting cells

Background

Malaria in pregnancy is associated with immunological abnormalities in the newborns, such as hampered T-helper 1 responses and increased T-regulatory responses, while the effect of maternal Plasmodium falciparum infection on foetal innate immunity is still controversial.

Materials and methods

The immunophenotype and cytokine release by dendritic cells (DC) and monocytes were evaluated in cord blood from 59 Beninese women with or without malaria infection by using flow cytometry.

Results

Accumulation of malaria pigment in placenta was associated with a partial maturation of cord blood myeloid and plasmacytoid DC, as reflected by an up-regulated expression of the major histocompatibility complex class II molecules, but not CD86 molecules. Cells of newborns of mothers with malaria pigment in their placenta also exhibited significantly increased cytokine responses upon TLR9 stimulation. In addition, maternal age and parity influenced the absolute numbers and activation status of cord blood antigen-presenting cells. Lastly, maternal age, but not parity, influenced TLR3, 4 and 9 responses in cord blood cells.

Discussion

Our findings support the view that placental parasitization, as indicated by the presence of malaria pigment in placental leukocytes, is significantly associated with partial maturation of different DC subsets and also to slightly increased responses to TLR9 ligand in cord blood. Additionally, other factors, such as maternal age and parity should be taken into consideration when analysing foetal/neonatal innate immune responses.

Conclusion

These data advocate a possible mechanism by which PAM may modulate foetal/neonatal innate immunity.

How might infant and paediatric immune responses influence malaria vaccine efficacy?

Naturally acquired immunity to malaria requires repeat infections yet does not engender sterile immunity or long-lasting protective immunologic memory. This renders infants and young children the most susceptible to malaria-induced morbidity and mortality, and the ultimate target for a malaria vaccine. The prevailing paradigm is that infants initially garner protection due to transplacentally transferred anti-malarial antibodies and other intrinsic factors such as foetal haemoglobin. As these wane infants have an insufficient immune repertoire to prevent genetically diverse Plasmodium infections and an inability to control malaria-induced immunopathology. This Review discusses humoral, cell-mediated and innate immune responses to malaria and how each contributes to protection – focusing on how deficiencies in infant and paediatric immune responses might influence malaria vaccine efficacy in this population. In addition, burgeoning evidence suggests a role for inhibitory receptors that limit immunopathology and guide the development of long-lived immunity. Precisely how age or malaria infections influence the function of these regulators is unknown. Therefore the possibility that infants may not have the immune-dexterity to balance effective parasite clearance with timely immune-regulation leading to protective immunologic memory is considered. And thus, malaria vaccines tested in adults and older children may not be predictive for trials conducted in infants.

Unraveling the impact of malaria exposure before birth

Lars Hviid discusses a research article in PLoS Medicine that explores whether prenatal exposure to malaria is associated with increased susceptibility to malarial infection and anemia in infancy.

Neonatal innate cytokine responses to BCG controlling T-cell development vary between populations

BACKGROUND

The protective effect of Mycobacterium bovis BCG vaccination against infection and atopy varies between populations.

OBJECTIVE

To identify differences in neonatal responses to BCG between diverse populations and study longitudinal associations with memory T-cell responses.

METHODS

Cord blood mononuclear cells were collected from Papua New Guinean (PNG) and Western Australian (WA) newborns. Toll-like receptor (TLR)-2, TLR4, and TLR9 mRNA expression and in vitro BCG-stimulated (+/-IFN-gamma priming) innate cytokine responses were compared. When PNG infants were 3 months old, PBMCs were stimulated in vitro with Mycobacterium-purified protein derivative (PPD) to determine memory T-cell responses.

RESULTS

BCG-induced IL-10 and IFN-gamma responses were significantly higher in cord blood mononuclear cells of PNG newborns, and TLR2 and TLR9 expression was significantly higher and TLR4 expression lower compared with WA newborns. High neonatal IL-10 and low IFN-gamma responses to BCG were found to promote the development of PPD-memory T(H)2 responses in infancy, whereas neonatal BCG-TNFalpha responses inhibited the development of PPD-IL 10 responses. When primed with IFN-gamma, BCG-induced TNF-alpha, IL-12p70, and in particular IFN-gamma responses were enhanced to a significantly higher extent in WA than in PNG newborns. In response to IFN-gamma priming and BCG stimulation, natural killer cells of WA newborns produced IFN-gamma, whereas natural killer cells of PNG newborns contributed only indirectly to this response.

CONCLUSION

Neonatal BCG-related innate immune responses control the differentiation of T(H) memory responses and vary between populations. This may explain differences in the effects of BCG vaccination between populations.

Placental malaria increases malaria risk in the first 30 months of life

BACKGROUND

Plasmodium falciparum infection during pregnancy is associated with stillbirth, fetal growth restriction, and low birth weight. An additional consequence may be increased risk of malaria in early life, although the epidemiological evidence of this consequence is limited.

METHODS

A cohort of 527 children were observed actively every month for 30 months after delivery. Offspring of mothers with microscopically detectable placental P. falciparum infection at the time of delivery were defined as exposed. The outcome measure was malaria (parasitemia and fever). Analyses were performed using Cox proportional hazard models and were stratified by gravidity.

RESULTS

Overall, offspring of mothers with placental P. falciparum infection had a significantly higher risk of clinical malaria during the first 30 months of life (adjusted hazard ratio, 2.1; 95% confidence interval [CI], 1.2-3.7). The adjusted hazard ratio for offspring of multigravidae was 2.6 (95% CI, 1.3-5.3), and that for primigravidae was 1.5 (95% CI, 0.6-3.8). The offspring of placenta-infected primigravidae had no episodes of malaria during the first year of life.

CONCLUSIONS

Our findings show that active placental P. falciparum infection detected at delivery is associated with an approximately 2-fold greater risk of malaria during early life, compared with noninfection. The fact that persons born to infected multigravidae rather than primigravidae appear to be at greater risk emphasizes the importance of preventing malaria in mothers of all gravidities.