Fetal responses during placental malaria modify the risk of low birth weight

Interleukin-1 beta signals through the ERK signalling pathway to modulate human placental trophoblast migration and invasion in the first trimester of pregnancy

INTRODUCTION

Interleukin-1 beta (IL-1β) can promote cell migration, invasion and metastasis in various cancer cells. The mechanism of its role in human trophoblast has not been fully investigated. Therefore, we aimed to investigate the expression level of IL-1β in first trimester decidua and placenta and its potential role in regulation of extravillous trophoblast cell (EVT) invasion and migration.

METHODS

First trimester placenta and decidua were collected to study the expression levels of IL-1β and its receptors by immunohistochemical staining. Primary isolates of first trimester EVT or the HTR-8/SVneo trophoblast like cell line were used to assess migration and invasion. Matrix metalloproteinase levels were assessed by gelatin zymography and ELISA. The phosphorylation profile of signaling pathway proteins was detected with the Proteome Profiler Human Phospho-Kinase Array Kit. Differentially expressed proteins in cells was detected and verified by Western Blot.

RESULTS

IL-1β, its receptors and antagonist are expressed in first trimester placenta and decidua, exogenous IL-1β stimulates trophoblast cell outgrowth, migration and invasion through the ERK signaling pathway. IL-1β was significantly increased in the placenta at 6-7 weeks gestation compared with 8-9 weeks gestation (P < 0.0001). Transwell and RTCA assays indicated that IL-1β stimulates the invasion and migration of EVT. In addition, IL-1β promoted the phosphorylation of ERK 1/2. It also promoted the expression of MMP2 and MMP9 in EVT as demonstrated by gelatin zymography assay and enzyme linked immunosorbent assay.

DISCUSSION

This study demonstrated IL-1β expression in placenta and decidua, and that it regulates EVT invasion and migration.

Pathogenicity and virulence of malaria: Sticky problems and tricky solutions

Infections with Plasmodium falciparum and Plasmodium vivax cause over 600,000 deaths each year, concentrated in Africa and in young children, but much of the world's population remain at risk of infection. In this article, we review the latest developments in the immunogenicity and pathogenesis of malaria, with a particular focus on P. falciparum, the leading malaria killer. Pathogenic factors include parasite-derived toxins and variant surface antigens on infected erythrocytes that mediate sequestration in the deep vasculature. Host response to parasite toxins and to variant antigens is an important determinant of disease severity. Understanding how parasites sequester, and how antibody to variant antigens could prevent sequestration, may lead to new approaches to treat and prevent disease. Difficulties in malaria diagnosis, drug resistance, and specific challenges of treating P. vivax pose challenges to malaria elimination, but vaccines and other preventive strategies may offer improved disease control.

Complement System Activation Is a Plasma Biomarker Signature during Malaria in Pregnancy

Malaria in pregnancy (MiP) is a public health problem in malaria-endemic areas, contributing to detrimental outcomes for both mother and fetus. Primigravida and second-time mothers are most affected by severe anemia complications and babies with low birth weight compared to multigravida women. Infected erythrocytes (IE) reach the placenta, activating the immune response by placental monocyte infiltration and inflammation. However, specific markers of MiP result in poor outcomes, such as low birth weight, and intrauterine growth restriction for babies and maternal anemia in women infected with Plasmodium falciparum are limited. In this study, we identified the plasma proteome signature of a mouse model infected with Plasmodium berghei ANKA and pregnant women infected with Plasmodium falciparum infection using quantitative mass spectrometry-based proteomics. A total of 279 and 249 proteins were quantified in murine and human plasma samples, of which 28% and 30% were regulated proteins, respectively. Most of the regulated proteins in both organisms are involved in complement system activation during malaria in pregnancy. CBA anaphylatoxin assay confirmed the complement system activation by the increase in C3a and C4a anaphylatoxins in the infected plasma compared to non-infected plasma. Moreover, correlation analysis showed the association between complement system activation and reduced head circumference in newborns from Pf-infected mothers. The data obtained in this study highlight the correlation between the complement system and immune and newborn outcomes resulting from malaria in pregnancy.

Fetal Cytokine Balance, Erythropoietin and Thalassemia but Not Placental Malaria Contribute to Fetal Anemia Risk in Tanzania

Fetal anemia is common in malaria-endemic areas and a risk factor for anemia as well as mortality during infancy. Placental malaria (PM) and red cell abnormalities have been proposed as possible etiologies, but the relationship between PM and fetal anemia has varied in earlier studies, and the role of red cell abnormalities has not been studied in malaria-endemic areas. In a Tanzanian birth cohort study designed to elucidate the pathogenesis of severe malaria in young infants, we performed a cross-sectional analysis of risk factors for fetal anemia. We determined PM status, newborn red cell abnormalities, and maternal and cord blood levels of iron regulatory proteins, erythropoietin (EPO), cytokines and cytokine receptors. We examined the relationship between these factors and fetal anemia. Fetal anemia was present in 46.2% of the neonates but was not related to PM. Maternal iron deficiency was common (81.6%), most frequent in multigravidae, and interacted with parity to modify risk of fetal anemia, but it was not directly related to risk. Among offspring of iron-deficient women, the odds of fetal anemia increased with fetal α⁺-thalassemia, as well as these patterns of cord blood cytokines: increased cord IL-6, decreased TNF-RI, and decreased sTfR. The EPO response to fetal anemia was low or absent and EPO levels were significantly decreased in newborns with the most severe anemia. This study from an area of high malaria transmission provides evidence that 1) fetal α⁺-thalassemia and cytokine balance, but not PM at delivery, are related to fetal anemia; 2) maternal iron deficiency increases the risk that other factors may cause fetal anemia; and 3) fetal anemia has a multifactorial etiology that may require a variety of interventions, although measures that reduce maternal iron deficiency may be generally beneficial.

Early malaria infection, dysregulation of angiogenesis, metabolism and inflammation across pregnancy, and risk of preterm birth in Malawi: A cohort study

BACKGROUND

Malaria in pregnancy is associated with adverse birth outcomes. However, the underlying mechanisms remain poorly understood. Tight regulation of angiogenic, metabolic, and inflammatory pathways are essential for healthy pregnancies. We hypothesized that malaria disrupts these pathways leading to preterm birth (PTB).

METHODS AND FINDINGS

We conducted a secondary analysis of a randomized trial of malaria prevention in pregnancy conducted in Malawi from July 21, 2011, to March 18, 2013. We longitudinally assessed circulating mediators of angiogenic, metabolic, and inflammatory pathways during pregnancy in a cohort of HIV-negative women (n = 1,628), with a median age of 21 years [18, 25], and 562 (35%) were primigravid. Pregnancies were ultrasound dated, and samples were analyzed at 13 to 23 weeks (Visit 1), 28 to 33 weeks (Visit 2), and/or 34 to 36 weeks (Visit 3). Malaria prevalence was high; 70% (n = 1,138) had PCR-positive Plasmodium falciparum infection at least once over the course of pregnancy and/or positive placental histology. The risk of delivering preterm in the entire cohort was 20% (n = 304/1506). Women with malaria before 24 weeks gestation had a higher risk of PTB (24% versus 18%, p = 0.005; adjusted relative risk [aRR] 1.30, 95% confidence interval [CI] 1.04-1.63, p = 0.021); and those who were malaria positive only before week 24 had an even greater risk of PTB (28% versus 17%, p = 0.02; with an aRR of 1.67, 95% CI 1.20-2.30, p = 0.002). Using linear mixed-effects modeling, malaria before 24 weeks gestation was associated with altered kinetics of inflammatory (C-Reactive Protein [CRP], Chitinase 3-like protein-1 [CHI3L1], Interleukin 18 Binding Protein [IL-18BP], soluble Tumor Necrosis Factor receptor II [sTNFRII], soluble Intercellular Adhesion Molecule-1 [sICAM-1]), angiogenic (soluble Endoglin [sEng]), and metabolic mediators (Leptin, Angiopoietin-like 3 [Angptl3]) over the course of pregnancy (χ2 > 13.0, p ≤ 0.001 for each). Limitations include being underpowered to assess the impact on nonviable births, being unable to assess women who had not received any antimalarials, and, because of the exposure to antimalarials in the second trimester, there were limited numbers of malaria infections late in pregnancy.

CONCLUSIONS

Current interventions for the prevention of malaria in pregnancy are initiated at the first antenatal visit, usually in the second trimester. In this study, we found that many women are already malaria-infected by their first visit. Malaria infection before 24 weeks gestation was associated with dysregulation of essential regulators of angiogenesis, metabolism, and inflammation and an increased risk of PTB. Preventing malaria earlier in pregnancy may reduce placental dysfunction and thereby improve birth outcomes in malaria-endemic settings.

Differential Activation of Fetal Hofbauer Cells in Primigravidas Is Associated with Decreased Birth Weight in Symptomatic Placental Malaria

Background

Placental malaria is a leading global cause of low birth weight neonates, especially in first-time mothers. To better understand the role of innate immunity in placental malaria, we investigated the relationships between histopathological markers of placental malaria, fetal and maternal macrophage responses, and perinatal outcomes in a cross-sectional case control study of pregnant women presenting with symptomatic malaria at the time of delivery.

Results

Primigravidas showed increased hemozoin deposition in placental villi (p=0.02), syncytiotrophoblasts (p=0.01), and fetal Hofbauer cells (p=0.01). The percentage of hemozoin-positive villi negatively correlated with infant birth weight (regression coefficient [b] = -0.03 kg decrease in birth weight per % increase in hemozoin-positive villi, p=0.035). Malaria-infected placentas showed a twofold increase in Hofbauer cells (p<0.001) and maternal macrophages (p<0.001). Placental malaria was associated with a threefold increase in the percentage of M2 maternal macrophages (19.2% vs 6.4%, p=0.01). Primigravidas showed a significant decrease in the Hofbauer cell M2-percentage in placental malaria (92.7% vs. 97.0%, p=0.04), which was predictive of infant birth weight (b=0.08 kg increase in birth weight per % increase in M2 Hofbauer cells, p=0.001). There was no association between maternal macrophage response and infant birth weights.

Conclusions

Placentas with malarial infection had increased numbers of fetal Hofbauer cells in the villous stroma and maternal macrophages in the intervillous space. In primigravidas, decreased anti-inflammatory M2-type Hofbauer cells were predictive of lower birth weight. M2-type maternal macrophages were increased in placental malaria, but there was no association with gravidity or birth weight. These results suggested a protective role of M2 Hofbauer cells in fetal growth restriction.

Systemic Inflammatory Response to Malaria During Pregnancy Is Associated With Pregnancy Loss and Preterm Delivery

Background

Pregnancy malaria (PM) is associated with a proinflammatory immune response characterized by increased levels of cytokines and chemokines such as tumor necrosis factor-α, interferon-γ, interleukin 10 (IL-10), and CXCL9. These changes are associated with poor outcomes including low birthweight delivery and maternal anemia. However, it is unknown if inflammatory pathways during malaria are related to pregnancy loss and preterm delivery (PTD).

Methods

Cytokine and chemokine levels were measured in maternal peripheral blood at enrollment, gestational week 30-32, and delivery, and in placental blood, of 638 women during a longitudinal cohort study in Ouelessebougou, Mali. Plasmodium falciparum infection was assessed by blood smear microscopy at all visits.

Results

PM was associated with increased levels of cytokines and chemokines including IL-10 and CXCL9. In a competing risks model adjusted for known covariates, high CXCL9 levels measured in the peripheral blood during pregnancy were associated with increased risk of pregnancy loss and PTD. At delivery, high IL-10 levels in maternal blood were associated with an increase in pregnancy loss, and increased IL-1β levels in placental blood were associated with pregnancy loss and PTD.

Conclusions

PM is associated with increased proinflammatory cytokine and chemokine levels in placental and maternal peripheral blood. Systemic inflammatory responses to malaria during pregnancy predict increased risk of pregnancy loss and PTD.

Clinical Trials Registration

NCT01168271.

Malaria during Pregnancy

One hundred and twenty-five million women in malaria-endemic areas become pregnant each year (see Dellicour et al. PLoS Med7: e1000221 [2010]) and require protection from infection to avoid disease and death for themselves and their offspring. Chloroquine prophylaxis was once a safe approach to prevention but has been abandoned because of drug-resistant parasites, and intermittent presumptive treatment with sulfadoxine-pyrimethamine, which is currently used to protect pregnant women throughout Africa, is rapidly losing its benefits for the same reason. No other drugs have yet been shown to be safe, tolerable, and effective as prevention for pregnant women, although monthly dihydroartemisinin-piperaquine has shown promise for reducing poor pregnancy outcomes. Insecticide-treated nets provide some benefits, such as reducing placental malaria and low birth weight. However, this leaves a heavy burden of maternal, fetal, and infant morbidity and mortality that could be avoided. Women naturally acquire resistance to Plasmodium falciparum over successive pregnancies as they acquire antibodies against parasitized red cells that bind chondroitin sulfate A in the placenta, suggesting that a vaccine is feasible. Pregnant women are an important reservoir of parasites in the community, and women of reproductive age must be included in any elimination effort, but several features of malaria during pregnancy will require special consideration during the implementation of elimination programs.

Optimization of BeWo model to investigate placental responses to Plasmodium falciparum infected erythrocytes

Background

Establishment of an in vitro model to study placental malaria is essential for understanding the biology and pathogenesis of placental malaria. We defined experimental variables for obtaining responses of BeWo cells to placental binding Plasmodium falciparum infected erythrocytes (IE, CS2 parasites).

Materials and methods

Experimental variables included i) concentration of forskolin, a cyclic adenosine monophosphate inducer important in the induction of syncytialisation of BeWo, ii) suitable period of incubating BeWo with forskolin, and iii) ratio of IE to BeWo cells and length of incubation to induce physiological changes in BeWo cells, including the vasculogenic factors vascular endothelial growth factor A (VEGFA), endoglin, and angiopoietin-2; an anti-angiogenic factor (inhibin A); a regulator of cell growth, mammalian target of rapamycin (mTOR); a chemokine (IL-8); and the cytokine macrophage inhibition factor. The human hormone, chorionic gonadotrophin was used as a marker for syncytialisation.

Results

We showed that 72 hrs incubation of BeWo with 10 μm forskolin resulted in higher levels of syncytialisation and hCG secretion. Overall, the best condition was to co-culture syncytialised BeWo with a 10:1 ratio of IE for 48 hours. Under these conditions, when co-cultured with IE, BeWo produced increased amounts of IL-8 (p=0.0001), VEGF (p=0.001) and endoglin (p=0.001).

Conclusion

The model can be used to evaluate the impact of IE, inflammatory cytokines and other factors associated with placental malaria on syncytiotrophoblast function.

Materno-foetal leptin and insulin-like growth factor in low birth weight neonates

Low birth weight (LBW) is a health concern in developing countries. Leptin and insulin-like growth factor-I (IGF-I) are factors that influence LBW. A case-control study was conducted at Medani hospital, Sudan. Cases were women who had LBW deliveries ( 2,500 g) and controls were women with normal-weight babies ( 2.500 – 4,000 g). Sociodemographic and obstetrical characteristics were gathered from both groups and leptin and IGF-I levels were measured by ELISA. Cases and controls (45 in each arm) were matched in their basic data. The median (interquartile) of maternal leptin levels [9.9 (1.9 – 21.8) vs. 16.0 (9.6 – 20.8), ng/ml; P0.001] and IGF-I [1.6 (0.7 – 20.0) vs. 6.1 (4.3 – 7.1) ng/ml ; P 0.001] were significantly lower in cases than in controls. Likewise, cord serum leptin [5.8 (2.1 – 12.6) vs. 20.0 (5.1 – 37.8) ng/ml; P0.001] and cord serum IGF-I [1.7 (1.3 – 2.0) vs. 6.9 (5.9 – 7.4) ng/ml; P0.001] levels were significantly lower in cases than in controls. Significant positive correlation was found between birth weight and cord leptin ( r0.398), maternal ( r0.795) and cord ( r0.863) IGF-I levels. Maternal and cord leptin and IGF-I levels were significantly lower in LBW babies.

Impact of placental Plasmodium falciparum malaria infection on the Cameroonian maternal and neonate's plasma levels of some cytokines known to regulate T cells differentiation and function

BACKGROUND

The impact of placental malaria (PM) infection on the expression profile of some cytokines known to regulate T cell differentiation and function and their influence on birth weight remain unclear. Moreover, there are no reports showing the relationship between PM and IL-27 or IL-28A. This study therefore sought to investigate whether placental P. falciparum infection alters the expression profile of the cytokines IL-28A, IL-27, IL-17E and IL-6 in mothers and their new born.

METHODS

In a cross-sectional study conducted between 2013 and 2015 in Yaoundé, Cameroon, peripheral, placental and cord blood samples were collected from 108 women at delivery. Parasitaemia was determined microscopically and haemoglobin levels determined using a Coulter counter. Plasma levels of cytokines (IL-28A, IL-27, IL-17E and IL-6) were measured by Luminex magnetic screening assay.

RESULTS

Malaria parasite density in placenta impression smear associated negatively with maternal haemoglobin level (P < 0.0001) and baby birth weight (P = 0.016). While IL-17E, IL-27 and IL-28A levels were significantly higher in placental and cord plasma than in peripheral (P < 0.0001, < 0.001 and P = 0.026, respectively), an opposite relationship was observed with IL-6 (P = 0.0018). Multivariate analysis confirmed results of univariate analysis where the presence of malaria parasites or pigments in placenta tissue impression smears correlated with decrease levels of maternal IL-17E, IL-27 and IL-28A and neonate levels of IL-28A and IL-17E (0.0001 ≤ P ≤ 0.02). Placental and peripheral parasitaemias also correlated positively with peripheral plasma levels of IL-6 (rs = 0.18, P = 0.05 and rs = 0.17, P = 0.07, respectively). In addition, high maternal haemoglobin level associated with increasing levels of IL-17E, IL-27 and IL-28A in peripheral plasma (0.002 ≤ P ≤ 0.018) and high placental and cord plasma levels of these cytokines associated with increasing birth weight (0.0001 ≤ P ≤ 0.0027).

CONCLUSIONS

Placental malaria downregulates maternal plasma levels of IL-17E, IL-27 and IL-28A and neonates' plasma levels of IL-17E and IL-28A cytokines, which could help for parasite clearance and increase child birth weight. The study is expected to provide leads that should help identify potential biomarkers for improved birth weight and therapeutic interventions.

Heme-mediated apoptosis and fusion damage in BeWo trophoblast cells

Placental malaria (PM) is a complication associated with malaria infection during pregnancy that often leads to abortion, premature delivery, intrauterine growth restriction and low birth weight. Increased levels of circulating free heme, a by-product of Plasmodium-damaged erythrocytes, is a major contributor to inflammation, tissue damage and loss of blood brain barrier integrity associated with fatal experimental cerebral malaria. However, the role of heme in PM remains unknown. Proliferation and apoptosis of trophoblasts and fusion of the mononucleated state to the syncytial state are of major importance to a successful pregnancy. In the present study, we examined the effects of heme on the viability and fusion of a trophoblast-derived cell line (BeWo). Results indicate that heme induces apoptosis in BeWo cells by activation of the STAT3/caspase-3/PARP signaling pathway. In the presence of forskolin, which triggers trophoblast fusion, heme inhibits BeWo cell fusion through activation of STAT3. Understanding the effects of free plasma heme in pregnant women either due to malaria, sickle cell disease or other hemolytic diseases, will enable identification of high-risk women and may lead to discovery of new drug targets against associated adverse pregnancy outcome.

Designing a VAR2CSA-based vaccine to prevent placental malaria

Placental malaria (PM) due to Plasmodium falciparum is a major cause of maternal, fetal and infant mortality, but the mechanisms of pathogenesis and protective immunity are relatively well-understood for this condition, providing a path for vaccine development. P. falciparum parasites bind to chondroitin sulfate A (CSA) to sequester in the placenta, and women become resistant over 1–2 pregnancies as they acquire antibodies that block adhesion to CSA. The protein VAR2CSA, a member of the PfEMP1 variant surface antigen family, mediates parasite adhesion to CSA, and is the leading target for a vaccine to prevent PM. Obstacles to PM vaccine development include the large size (~350 kD), high cysteine content, and sequence variation of VAR2CSA. A number of approaches have been taken to identify the combination of VAR2CSA domains and alleles that can induce broadly active antibodies that block adhesion of heterologous parasite isolates to CSA. This review summarizes these approaches, which have examined VAR2CSA fragments for binding activity, antigenicity with naturally acquired antibodies, and immunogenicity in animals for inducing anti-adhesion or surface-reactive antibodies. Two products are expected to enter human clinical studies in the near future based on N-terminal VAR2CSA fragments that have high binding affinity for CSA, and additional proteins preferentially expressed by placental parasites are also being examined for their potential contribution to a PM vaccine.

Peripheral and placental biomarkers in women with placental malaria: a systematic review

Placental malaria (PM) causes significant morbidity in mothers and infants. Diagnosis of PM during pregnancy is however problematic due to placental sequestration of parasites. Host biomarkers may therefore be used as a diagnostic method. In this systematic review most studies focused on inflammatory markers. A trend was observed for increased IL-10 and TNF-α in PM positives. These markers are however unspecific, thus a combination of multiple biomarkers involved in different pathophysiological pathways of PM is indicated. Of interest are inflammatory markers (TNF-R2, CXCL-13), markers of lipid metabolism (APO-B), angiogenesis (sFlt-1) and hormones (estradiol). As the majority of published studies tested biomarker levels only at delivery, more longitudinal cohort studies will be necessary to detect biomarkers during pregnancy that can predict PM.

Induction of pro-inflammatory response of the placental trophoblast by Plasmodium falciparum infected erythrocytes and TNF

Background

Plasmodium falciparum placental malaria is characterized by the sequestration of infected erythrocytes (IEs) in the placental intervillous space via adherence to chondroitin sulphate A (CSA), production of inflammatory molecules, and leukocytes infiltration. Previous reports suggest that the syncytiotrophoblast (ST) immunologically responds to IEs contact. This study explores the inflammatory response induced in BeWo cells by adherence of IEs and TNFstimulation.

Methods

A non-syncitialized BeWo cells (trophoblast model) were used to evaluate its response to CSA-adherents IEs (FCB1csa, FCB2csa, FCR3csa, 3D7csa) and TNF stimulation. Expression of membrane ICAM-1 (mICAM-1) receptor in BeWo cells was quantified by flow cytometry and the IL-8, IL-6 and soluble ICAM-1 (sICAM-1) concentrations were quantified by enzyme-linked immunosorbentassay (ELISA) in BeWo stimulated supernatants.

Results

BeWo cells stimulated with TNF and CSA-adherents IEs of FCB1csa and 3D7csa (strains with higher adhesion) increase the expression of ICAM-1 on the surface of cells and the secretion of immune factors IL-8, IL-6 and sICAM-1. This inflammatory response appears to be related to the level of adherence of IEs because less adherent strains do not induce significant changes.

Conclusions

It was found that BeWo cells responds to CSA-IEs and to TNF favouring a placental pro-inflammatory environment, evidenced by increases in the expression of membrane mICAM-1 and release of soluble ICAM-1, as well as the IL-8 and IL-6 secretion. The expression of ICAM-1 in BeWo cells might be associated to an increase in leukocyte adhesion to the trophoblast barrier, promoting greater inflammation, while the sICAM-1 release could be a protection mechanism activated by trophoblastic cells, in order to regulate the local inflammatory response.

Cytokine profiles at birth predict malaria severity during infancy

BACKGROUND

Severe malaria risk varies between individuals, and most of this variation remains unexplained. Here, we examined the hypothesis that cytokine profiles at birth reflect inter-individual differences that persist and influence malaria parasite density and disease severity throughout early childhood.

METHODS AND FINDINGS

Cytokine levels (TNF-α, IFN-γ, IL-1β, IL-4, IL-5, IL-6 and IL-10) were measured at birth (cord blood; N=783) and during subsequent routine follow-up visits (peripheral blood) for children enrolled between 2002 and 2006 into a birth cohort in Muheza, Tanzania. Children underwent blood smear and clinical assessments every 2-4 weeks, and at the time of any illness. Cord blood levels of all cytokines were positively correlated with each other (Spearman's rank correlation). Cord levels of IL-1β and TNF-α (but not other cytokines) correlated with levels of the same cytokine measured at routine visits during early life (P < 0.05). Higher cord levels of IL-1β but not TNF-α were associated with lower parasite densities during infancy (P=0.003; Generalized Estimating Equation (GEE) method), with an average ~40% reduction versus children with low cord IL-1β levels, and with decreased risk of severe malaria during follow-up (Cox regression): adjusted hazard ratio (95% CI) 0.60 (0.39-0.92), P = 0.02.

CONCLUSION

IL-1β levels at birth are related to future IL-1β levels as well as the risk of severe malaria in early life. The effect on severe malaria risk may be due in part to the effect of inflammatory cytokines to control parasite density.

Diagnosing malaria in pregnancy: an update

Pregnancy malaria (PM) due to Plasmodium falciparum is a major cause of morbidity and mortality for women and their offspring, but is difficult to recognize and diagnose. During PM, parasites typically sequester in the placenta, whereas peripheral blood smears often appear negative. In addition, many infected women remain asymptomatic, especially in areas of high transmission where systemic immunity is high, although sequelae including maternal anemia and intrauterine growth retardation develop insidiously and increase mortality. New rapid diagnostic tests (RDTs) have shown promise for malaria diagnosis in nonpregnant individuals, including a product recently approved by the US FDA for use in the USA. However, the sensitivity and specificity of RDTs for diagnosis of PM may be suboptimal. Here, we review the methods that are used to detect or diagnose PM, including blood smear microscopy, RDTs, PCR-based methods, and finally placental histology, which is often cited as the gold standard for use in research studies and clinical trials.

Intravital placenta imaging reveals microcirculatory dynamics impact on sequestration and phagocytosis of Plasmodium-infected erythrocytes

Malaria in pregnancy is exquisitely aggressive, causing a range of adverse maternal and fetal outcomes prominently linked to Plasmodium-infected erythrocyte cytoadherence to fetal trophoblast. To elucidate the physiopathology of infected erythrocytes (IE) sequestration in the placenta we devised an experimental system for intravital placental examination of P. berghei-infected mice. BALB/c females were mated to C57Bl/6 CFP+ male mice and infected with GFP+ P. berghei IE, and at gestational day 18, placentas were exposed for time-lapse imaging acquisition under two-photon microscopy. Real-time images and quantitative measurements revealed that trophoblast conformational changes transiently restrain blood flow in the mouse placental labyrinth. The complex dynamics of placental microcirculation promotes IE accumulation in maternal blood spaces with low blood flow and allows the establishment of stable IE-trophoblast contacts. Further, we show that the fate of sequestered IE includes engulfment by both macrophagic and trophoblastic fetal-derived cells. These findings reinforce the current paradigm that IE interact with the trophoblast and provide definitive evidence on two novel pathogenesis mechanisms: (1) trophoblast layer controls placental microcirculation promoting IE sequestration; and (2) fetal-derived placental cells engulf sequestered IE.

Malaria in pregnancy is exquisitely aggressive, causing a range of adverse effects impacting maternal and fetal health. Many of those effects are thought to derive from placental sequestration of red blood cells infected with the malaria parasite (Plasmodium falciparum) eliciting a placental inflammatory response that impairs maternal-fetal exchanges. We developed an experimental system for intravital microscopy to directly observe the course of placental infection in a mouse model of pregnancy-associated malaria. We found that microcirculation in infected placentas showed areas of low blood flow that promote sequestration of infected red blood cells. Furthermore, we observed that sequestered infected red blood cells are targeted and phagocytosed by fetal-derived cells in the materno-fetal interface. This work provides the first ever in vivo evidence that unique placental microcirculatory features promote infected red blood cell sequestration, implying a vascular component in placental malaria pathogenesis. Moreover, we reinforce the notion that fetal-derived cells contribute to the placental response against sequestered infected red blood cells.

Genes involved in host-parasite interactions can be revealed by their correlated expression

Molecular interactions between a parasite and its host are key to the ability of the parasite to enter the host and persist. Our understanding of the genes and proteins involved in these interactions is limited. To better understand these processes it would be advantageous to have a range of methods to predict pairs of genes involved in such interactions. Correlated gene expression profiles can be used to identify molecular interactions within a species. Here we have extended the concept to different species, showing that genes with correlated expression are more likely to encode proteins, which directly or indirectly participate in host–parasite interaction. We go on to examine our predictions of molecular interactions between the malaria parasite and both its mammalian host and insect vector. Our approach could be applied to study any interaction between species, for example, between a host and its parasites or pathogens, but also symbiotic and commensal pairings.

CXC ligand 9 response to malaria during pregnancy is associated with low-birth-weight deliveries

Placental infection with Plasmodium falciparum is associated with increased levels of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ), and previous studies have associated increased levels of these cytokines with low birth weight (LBW), especially for malaria-infected primigravidae. To define the contribution of TNF-α and IFN-γ networks to placental-malaria-associated LBW, we measured chemokines induced by TNF-α and IFN-γ and related them to birth weight in a birth cohort of 782 mother-infant pairs residing in an area of P. falciparum holoendemicity in Tanzania. Among primigravidae, levels of CCL2, CXC ligand 9 (CXCL9), and CXCL13 were significantly higher during malaria infection in both the placenta and peripheral blood. Placental CXCL9 and CXCL13 levels were also higher in placental blood from secundigravidae and multigravidae. In multivariate analyses adjusted for known predictors of birth weight, malaria-infected primigravidae with placental CXCL9 levels in the lowest tertile gave birth to babies who weighed 610 g more than babies born to mothers with high CXCL9 levels. CXCL9 expression is induced by IFN-γ, and the strong association between birth weight and placental CXCL9 is consistent with previous observations relating IFN-γ to poor pregnancy outcomes.

Quantification of the burden and consequences of pregnancy-associated malaria in the Democratic Republic of the Congo

BACKGROUND

Pregnancy-associated malaria (PAM) produces poor birth outcomes, but its prevalence is commonly estimated in convenience samples.

METHODS

We assessed the prevalence of malaria using real-time polymerase chain reaction (PCR) and estimated the consequences of infection on birth outcomes, using specimens from a nationally representative sample of 4570 women of childbearing age (WOCBA) responding to the 2007 Demographic and Health Survey in Democratic Republic of the Congo (DRC).

RESULTS

Overall, 31.2% (95% confidence interval [CI], 29.2-33.1) of WOCBA were parasitemic, which was significantly more common in pregnant (37.2% [31.0-43.5]) than nonpregnant women (30.4% [CI, 28.4-32.5], prevalence ratio [PR] 1.22 [1.02-1.47]). Plasmodium falciparum was highest among pregnant women (36.6% vs 28.8%, PR 1.27 [1.05-1.53]). By contrast, P malariae was less common in pregnant (0.6%) compared with nonpregnant women (2.7%, PR 0.23 [0.09-0.56]). Extrapolation of the prevalence estimate to the population at risk of malaria in DRC suggests 1.015 million births are affected by P falciparum infection annually, and that adherence to preventive measures could prevent up to 549 000 episodes of pregnancy-associated malaria and 47 000 low-birth-weight births.

CONCLUSIONS

Pregnancy-associated malaria and its consequences are highly prevalent in the DRC. Increasing the uptake of malaria preventive measures represents a significant opportunity to improve birth outcomes and neonatal health.

Rethinking cerebral malaria pathology

PURPOSE OF REVIEW

Intense interventions are ongoing to combat malaria. Malaria mortality investigation remains as an intense area of study with controversies, competing models of pathogenesis, and a few carefully proceeding clinical trials. This review suggests a reframing of the question of cerebral malaria pathology in light of recent findings to focus on dissection of pathogenesis that will lead to effective treatments.

RECENT FINDINGS

Pediatric and adult manifestations of cerebral malaria within the retina allows for intense study of the clinical defined patients including the advent of multiple imaging modalities in endemic regions. Basic pathogenesis in mouse models and human studies, focused on cytokines, inflammation, cytoadherence, and endothelial activation, continues to be elucidated molecule by molecule. Coagulation is variably important and may serve as one of several unifying principles of current pathogenesis models. Parasite-derived molecules - surface or soluble - remain necessary but not sufficient to explain pathologic manifestations.

SUMMARY

As we close the gaps in the fight against global malaria, the question of cerebral malaria mortality remains a source of great concern. We currently have no effective means of reversal of coma or impacting mortality in the comatose patient. As transmission is broken, cerebral malaria will spread to older age groups in Africa where we expect mortality will be higher. Continued directed study of pathogenesis with the primary goal of efficacious interventions in the comatose is a necessity.

Sulfadoxine-pyrimethamine-based intermittent preventive treatment, bed net use, and antenatal care during pregnancy: demographic trends and impact on the health of newborns in the Kassena Nankana District, northeastern Ghana

Demographics and health practices of 2,232 pregnant women in rural northeastern Ghana and characteristics of their 2,279 newborns were analyzed to determine benefits associated with intermittent preventive treatment (IPTp), antenatal care, and/or bed net use during pregnancy. More than half reported bed net use, 90% reported at least two antenatal care visits, and > 82% took at least one IPTp dose of sulfadoxine-pyrimethamine. Most used a bed net and IPTp (45%) or IPTp alone (38%). Low birth weight (< 2,500 grams) characterized 18.3% of the newborns and was significantly associated with female sex, Nankam ethnicity, first-born status, and multiple births. Among newborns of primigravidae, IPTp was associated with a significantly greater birth weight, significantly fewer low birth weight newborns, improved hemoglobin levels, and less anemia. Babies of multigravidae derived no benefit to birth weight or hemoglobin level from single or multiple doses of sulfadoxine-pyrimethamine during pregnancy. No differences or benefits were seen when a bed net was the only protective factor.

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.

Plasma levels of apolipoprotein A1 in malaria-exposed primigravidae are associated with severe anemia

Background

Plasmodium falciparum placental malaria (PM) contributes to 10,000 maternal deaths due to severe anemia (SA) each year in Africa, primarily among primigravid women who are most susceptible. Increased levels of proinflammatory cytokines like TNF-α are associated with maternal anemia in first time mothers but not in other women. Here we aimed to identify additional changes in the plasma proteome associated with pregnancy malaria that may contribute to the development of malaria-related maternal anemia.

Principal Findings

A semi-quantitative mass spectrometry approach was used to compare the relative abundance of plasma proteins in anemic versus non-anemic women with PM. Levels of 24 proteins differed significantly between anemic and non-anemic primigravidae, including several lipid metabolism proteins and molecular transport proteins involved in the acute phase response signaling network. These differences were not observed in multigravid women who enjoy specific immunity that protect them from PM. In a confirmatory study of a larger cohort of primigravid women, levels of the lipid metabolism protein Apolipoprotein (Apo)-AI were significantly lower in PM+ women with SA.

Conclusions

Apo-AI levels are significantly lower in severely anemic primigravidae with PM, and ApoA1 levels positively correlate with hemoglobin levels in primigravid but not multigravid women. Apo-AI is known to have anti-inflammatory effects, and thus Apo-AI reductions may contribute to the inflammatory processes that result in SA.

Placental malaria is associated with reduced early life weight development of affected children independent of low birth weight

Background

Infection with Plasmodium falciparum during pregnancy contributes substantially to the disease burden in both mothers and offspring. Placental malaria may lead to intrauterine growth restriction or preterm delivery resulting in low birth weight (LBW), which, in general, is associated with increased infant morbidity and mortality. However, little is known about the possible direct impact of the specific disease processes occurring in PM on longer term outcomes such as subsequent retarded growth development independent of LBW.

Methods

In an existing West-African cohort, 783 healthy infants with a birth weight of at least 2,000 g were followed up during their first year of life. The aim of the study was to investigate if Plasmodium falciparum infection of the placenta, assessed by placental histology, has an impact on several anthropometric parameters, measured at birth and after three, six and 12 months using generalized estimating equations models adjusting for moderate low birth weight.

Results

Independent of LBW, first to third born infants who were exposed to either past, chronic or acute placental malaria during pregnancy had significantly lower weight-for-age (-0.43, 95% CI: -0.80;-0.07), weight-for-length (-0.47, 95% CI: -0.84; -0.10) and BMI-for-age z-scores (-0.57, 95% CI: -0.84; -0.10) compared to infants born to mothers who were not diagnosed with placental malaria (p = 0.019, 0.013, and 0.012, respectively). Interestingly, the longitudinal data on histology-based diagnosis of PM also document a sharp decline of PM prevalence in the Sukuta cohort from 16.5% in 2002 to 5.4% in 2004.

Conclusions

It was demonstrated that PM has a negative impact on the infant's subsequent weight development that is independent of LBW, suggesting that the longer term effects of PM have been underestimated, even in areas where malaria transmission is declining.