Molecular interactions in the placenta during malaria infection

The impact of human complement on the clinical outcome of malaria infection

The tropical disease malaria remains a major cause of global morbidity. Once transmitted to the human by a blood-feeding mosquito, the unicellular malaria parasite comes into contact with the complement system and continues to interact with human complement during its intraerythrocytic replication cycles. In the course of infection, both the classical and the alternative pathway of complement are activated, leading to parasite opsonization and lysis as well as the induction of complement-binding antibodies. While complement activity can be linked to the severity of malaria, it remains to date unclear, whether human complement is beneficial for protective immunity or if extensive complement reactions may rather enhance pathogenesis. In addition, the parasite has evolved molecular strategies to circumvent attack by human complement and has even developed means to utilize complement factors as mediators of host cell infection. In this review, we highlight current knowledge on the role of human complement for the progression of malaria infection. We discuss the various types of interactions between malaria parasites and complement factors with regard to immunity and infection outcome and set a special emphasis on the dual role of complement in the context of parasite fitness.

Reprogramming of red blood cell metabolism in Zika virus–infected donors

BACKGROUND

Diseases caused by arthropod-borne viruses remain a burden to global health; in particular, Zika virus (ZIKV) has been reported in 87 countries and territories. In healthy blood donors, ZIKV RNA can be detected in red blood cells (RBCs) months after infection, clearance of detectable nucleic acid in plasma, and seroconversion. However, little information is available on the impact of ZIKV infection to metabolism.

STUDY DESIGN AND METHODS

We applied mass spectrometry-based metabolomics and lipidomics approaches to investigate the impact of ZIKV infection on RBCs over the course of infection. ZIKV-infected blood donors (n = 25) were identified through molecular and serologic methods, which included nucleic acid amplification testing and real-time polymerase chain reaction (PCR) for detection of ZIKV RNA and enzyme-linked immunosorbent assay (ELISA) for detection of flavivirus-specific IgM and IgG.

RESULTS

In ZIKV RNA-positive donors, we observed lower glucose and lactate levels, and higher levels of ribose phosphate, suggestive of the activation of the pentose phosphate pathway. The top pathways altered in RBCs from ZIKV-IgM-positive donors include amino acid metabolism and biosynthesis, fatty acid metabolism and biosynthesis, linoleic acid and arachidonate metabolism and glutathione metabolism. RBCs from ZIKV-infected donors had increased levels of early glycolytic metabolites, and higher levels of metabolites of the pentose phosphate pathway. Alterations in acyl-carnitine and fatty acid metabolism are consistent with impaired membrane lipid homeostasis in RBCs from ZIKV IgM positive donors.

CONCLUSION

RBC from healthy blood donors who had been infected by ZIKV are characterized by long-lasting metabolic alterations even months after infection has resolved.

Effect of Plasmodium berghei infection on fetuses in pregnant BALB/c mice at two periods of pregnancy

Malaria is a disease caused by a protozoan of the genus Plasmodium in humans and vertebrates. It has a high morbidity and mortality rate, especially in pregnant women living in countries with high transmission rates. Murine models have been an excellent tool to evaluate the effects of malarial infection in the mother-fetus relationship. For this reason, we evaluated the effect of malarial infection on fetal development at the beginning and middle of the gestational period in BALB/c mice infected with Plasmodium berghei ANKA. Our results show that malarial infection at the beginning of pregnancy markedly affects the development of the fetus in size, weight, and development of its limbs so that the control of the pregnant mother is relevant at the beginning of gestation

A tablet derived from Andrographis paniculata complements dihydroartemisinin-piperaquine treatment of malaria in pregnant mice

OBJECTIVES

The use of standard antimalarial drugs, such as dihydroartemisinin-piperaquine (DHP) for the treatment of malaria during pregnancy is limited due to the risk of teratogenicity. The alternative is therefore required although few exist. Here we show a phytopharmaceutical drug derived from Andrographis paniculata (AS201-01), which is effective as herbal antimalarial both in vitro and in vivo and may be a suitable alternative when used in complementary treatment with DHP.

METHODS

Plasmodium berghei infected pregnant BALB/c mice were divided into four groups: G1 (negative control), G2 (AS201-01), G3 (DHP), and G4 (combination of DHP and AS201-01). Pheripheral blood was collected during therapy for counting parasitemia. Placental samples were analyzed for the expression of IFN-γ, TNF- α, IL-10, placental parasite counts and foetal morphology.

RESULTS

Groups G4 and G3 both showed a 100% inhibition of peripheral parasitemia. However, the treatment in G4 was found to be less effective than that in G2 and G3 in preventing placental parasitemia. The G4 treatment was able to reduce the expression of IFN-γ and IL-10, whereas TNF-α was not significantly different from the control group. Foetal morphologic abnormalities were observed in all groups except G2; G4 showed lower percentage of abnormalities compared to G3 and G1.

CONCLUSIONS

A combination of A. paniculata tablet (AS201-01) with DHP has the potential to reduce the toxicity of DHP in malaria treatment.

Impact of placental malaria on maternal, placental and fetal cord responses and its role in pregnancy outcomes in women from Blue Nile State, Sudan

Background

The sequestration of Plasmodium falciparum infected cells in the placenta results in placental malaria (PM). It activates the mother's immune cells and induces secretion of inflammatory cytokines, which might influence pregnancy outcomes. This study aims to investigate the cytokines (levels IL-4, IL-6, IL-10, IL-17A, and INF γ) in maternal peripheral, placental, and umbilical cord blood in response to PM and the extent to which this may influence maternal haemoglobin levels and birth weight.

Methods

A total of 185 consenting Sudanese women from Blue Nile State were enrolled at delivery time in a cross-sectional study conducted between Jan 2012-Dec 2015. Malaria infection in the collected maternal peripheral, placental, umbilical cord samples was determined microscopically, and ELISA was used to measure the plasma levels IL-4, IL-6, IL-10, IL-17A, and INF γ in the collected positive and negative malaria samples.

Results

Elevated levels of IL-4 and IL-10 and reduced levels of IL-6 were detected in the malaria positive samples in comparison to the negative ones in the three types of the samples investigated. Maternal, IL-4 and IL-10 were significantly higher in the samples collected from the PM infected group compared to the non-infected control (P < 0.001). While the absence of PM was significantly associated with the IL-6 and maternal IFN-γ levels, maternal IL-17A, placental and umbilical cord IFN-γ levels showed no significant difference (P = 0.214, P = 0.065, P = 0.536, respectively) due to infection. Haemoglobin level and birth weight were increased in the group with high levels of IL-6 and IL-17A, but not in the group with IL-4 and IL-10 levels. While significantly negative correlation was found between IFN-γ levels and birth weight for all three types of samples, only maternal peripheral IFN-γ level was significantly positively correlated with maternal haemoglobin (r = 0.171, P = 0.020).

Conclusion

These results suggest that PM induces mother’s immune response and impairs her cytokine profile, which might alter maternal haemoglobin levels and the baby's birth weight.

Using two phases of the CD4 T cell response to blood-stage murine malaria to understand regulation of systemic immunity and placental pathology in Plasmodium falciparum infection

Plasmodium falciparum infection and malaria remain a risk for millions of children and pregnant women. Here, we seek to integrate knowledge of mouse and human T helper cell (Th) responses to blood-stage Plasmodium infection to understand their contribution to protection and pathology. Although there is no complete Th subset differentiation, the adaptive response occurs in two phases in non-lethal rodent Plasmodium infection, coordinated by Th cells. In short, cellular immune responses limit the peak of parasitemia during the first phase; in the second phase, humoral immunity from T cell-dependent germinal centers is critical for complete clearance of rapidly changing parasite. A strong IFN-γ response kills parasite, but an excess of TNF compared with regulatory cytokines (IL-10, TGF-β) can cause immunopathology. This common pathway for pathology is associated with anemia, cerebral malaria, and placental malaria. These two phases can be used to both understand how the host responds to rapidly growing parasite and how it attempts to control immunopathology and variation. This dual nature of T cell immunity to Plasmodium is discussed, with particular reference to the protective nature of the continuous generation of effector T cells, and the unique contribution of effector memory T cells.

Antiplasmodial Activity Assay of 3-Chloro-4-(4-chlorophenoxy) Aniline Combinations with Artesunate or Chloroquine In Vitro and in a Mouse Model

Malaria is the eighth highest contributor to global disease burden with 212 million cases and 429,000 deaths reported in 2015. There is an urgent need to develop multiple target drug to curb growing resistance by Plasmodia due to use of single target drugs and lack of vaccines. Based on a previous study, 3-chloro-4-(4-chlorophenoxy) aniline (ANI) inhibits Plasmodia enoyl acyl carrier protein reductase. This study aimed at evaluating the antiplasmodial activity of ANI combinations with artesunate (AS) or chloroquine (CQ) against P. falciparum in vitro based on the semiautomated microdilution assay and P. berghei in vivo based on Peters' 4-day test. Data were analysed by linear regression using version 5.5 of Statistica, 2000. From the results, on the one hand, a combination of 1.1 ng/ml AS and 3.3 μg/ml of ANI inhibited 50% growth of W₂, while a combination of 0.8 ng/ml of AS and 2.6 μg/ml of ANI inhibited 50% growth of 3D₇. On the other hand, a combination of 22 ng/ml CQ and 3.7 μg/ml of ANI inhibited 50% growth of W₂, while a combination of 4.6 ng/ml CQ and 3.1 μg/ml of ANI inhibited 50% growth of 3D₇. In in vivo assays, a combination of ED₅₀ concentrations of AS and ANI cleared all parasites, while 1/2 and 1/4 ED₅₀ combinations inhibited 67.0% and 35.4% parasite growth, respectively. ED₅₀ combinations of CQ and ANI inhibited 81.0% growth of parasites, while 1/2 and 1/4 ED₅₀ combinations inhibited 27.3% and 10.2% parasite growth. Assuming a linear relationship between percentage chemosuppression and combination ratios, only 0.88 mg/kg of AS combined with 1.68 mg/kg of ANI or 1.78 mg/kg of CQ with 3.15 mg/kg of ANI inhibited 50% parasite growth in vivo. ANI combinations with AS or CQ are thus potential antimalarial drug combinations if their clinical efficacy and safety are ascertained.

Targeting delivery of partial VAR2CSA peptide guided N-2-Hydroxypropyl trimethyl ammonium chloride chitosan nanoparticles for multiple cancer types

To developing a multiple cancer types targeting drug delivery carrier system, a 28 amino acids from the VAR2CSA was synthesized as the placental CSA-binding peptide (plCSA-BP). Its specific binding ability to cancer cells was tested on cancer tissue array, and the results showed that plCSA-BP could bind to multiple cancer types. Then, the plCSA-BP was used as a guiding peptide to coat nanoparticles synthesized from N-2-HACC (CSA/HACC-NPs) which were loaded with prodigiosin (CSA/HACC-PNPs) or indocyanine green (CSA/HACC-INPs). The cancer cells specific targeting and efficacy of the CSA/HACC-PNPs were tested by different cancer cells in vitro and various cancer xenograft model in vivo. A scramble peptide (SCR) was used as control and synthesized SCR/HACC-PNPs and SCR/HACC-INPs. The results showed that the CSA/HACC-INPs could specifically uptake by JEG-3, PC3 and A594 cells, and the CSA/HACC-PNPs exhibited better anti-cancer activity and lower toxic effect in subcutaneous choriocarcinoma and prostatic tumor models compared with the free prodigiosin, HACC-PNPs and SCR/HACC-PNPs. So, the CSA/HACC-NPs could be used as a specific delivery carrier for multiple cancer types, and provided an alternate treatment option of various cancers with a single recipe.

Detecting eukaryotic microbiota with single-cell sensitivity in human tissue

BACKGROUND

Fetal growth restriction, pre-eclampsia, and pre-term birth are major adverse pregnancy outcomes. These complications are considerable contributors to fetal/maternal morbidity and mortality worldwide. A significant proportion of these cases are thought to be due to dysfunction of the placenta. However, the underlying mechanisms of placental dysfunction are unclear. The aim of the present study was to investigate whether adverse pregnancy outcomes are associated with evidence of placental eukaryotic infection.

RESULTS

We modified the 18S Illumina Amplicon Protocol of the Earth Microbiome Project and made it capable of detecting just a single spiked-in genome copy of Plasmodium falciparum, Saccharomyces cerevisiae, or Toxoplasma gondii among more than 70,000 human cells. Using this method, we were unable to detect eukaryotic pathogens in placental biopsies in instances of adverse pregnancy outcome (n = 199) or in healthy controls (n = 99).

CONCLUSIONS

Eukaryotic infection of the placenta is not an underlying cause of the aforementioned pregnancy complications. Possible clinical applications for this non-targeted, yet extremely sensitive, eukaryotic screening method are manifest.

Host-Parasite Interactions in Human Malaria: Clinical Implications of Basic Research

The malaria parasite, Plasmodium, is one of the oldest parasites documented to infect humans and has proven particularly hard to eradicate. One of the major hurdles in designing an effective subunit vaccine against the malaria parasite is the insufficient understanding of host–parasite interactions within the human host during infections. The success of the parasite lies in its ability to evade the human immune system and recruit host responses as physiological cues to regulate its life cycle, leading to rapid acclimatization of the parasite to its immediate host environment. Hence understanding the environmental niche of the parasite is crucial in developing strategies to combat this deadly infectious disease. It has been increasingly recognized that interactions between parasite proteins and host factors are essential to establishing infection and virulence at every stage of the parasite life cycle. This review reassesses all of these interactions and discusses their clinical importance in designing therapeutic approaches such as design of novel vaccines. The interactions have been followed from the initial stages of introduction of the parasite under the human dermis until asexual and sexual blood stages which are essential for transmission of malaria. We further classify the interactions as “direct” or “indirect” depending upon their demonstrated ability to mediate direct physical interactions of the parasite with host factors or their indirect manipulation of the host immune system since both forms of interactions are known to have a crucial role during infections. We also discuss the many ways in which this understanding has been taken to the field and the success of these strategies in controlling human malaria.

Complement Activation in Placental Malaria

Sixty percent of all pregnancies worldwide occur in malaria endemic regions. Pregnant women are at greater risk of malaria infection than their non-pregnant counterparts and have a higher risk of adverse birth outcomes including low birth weight resulting from intrauterine growth restriction and/or preterm birth. The complement system plays an essential role in placental and fetal development as well as the host innate immune response to malaria infection. Excessive or dysregulated complement activation has been associated with the pathobiology of severe malaria and with poor pregnancy outcomes, dependent and independent of infection. Here we review the role of complement in malaria and pregnancy and discuss its part in mediating altered placental angiogenesis, malaria-induced adverse birth outcomes, and disruptions to the in utero environment with possible consequences on fetal neurodevelopment. A detailed understanding of the mechanisms underlying adverse birth outcomes, and the impact of maternal malaria infection on fetal neurodevelopment, may lead to biomarkers to identify at-risk pregnancies and novel therapeutic interventions to prevent these complications.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.

Malaria in Pregnancy Interacts with and Alters the Angiogenic Profiles of the Placenta

Malaria in pregnancy remains a substantial public health problem in malaria-endemic areas with detrimental outcomes for both the mother and the foetus. The placental changes that lead to some of these detrimental outcomes have been studied, but the mechanisms that lead to these changes are still not fully elucidated. There is some indication that imbalances in cytokine cascades, complement activation and angiogenic dysregulation might be involved in the placental changes observed. Nevertheless, the majority of studies on malaria in pregnancy (MiP) have come from areas where malaria transmission is high and usually restricted to Plasmodium falciparum, the most pathogenic of the malaria parasite species. We conducted a cross-sectional study in Cruzeiro do Sul, Acre state, Brazil, an area of low transmission and where both P. vivax and P. falciparum circulate. We collected peripheral and placental blood and placental biopsies, at delivery from 137 primigravid women and measured levels of the angiogenic factors angiopoietin (Ang)-1, Ang-2, their receptor Tie-2, and several cytokines and chemokines. We measured 4 placental parameters (placental weight, syncytial knots, placental barrier thickness and mononuclear cells) and associated these with the levels of angiogenic factors and cytokines. In this study, MiP was not associated with severe outcomes. An increased ratio of peripheral Tie-2:Ang-1 was associated with the occurrence of MiP. Both Ang-1 and Ang-2 had similar magnitudes but inverse associations with placental barrier thickness. Malaria in pregnancy is an effect modifier of the association between Ang-1 and placental barrier thickness.

Low Fetal Weight is Directly Caused by Sequestration of Parasites and Indirectly by IL-17 and IL-10 Imbalance in the Placenta of Pregnant Mice with Malaria

The sequestration of infected erythrocytes in the placenta can activate the syncytiotrophoblast to release cytokines that affect the micro-environment and influence the delivery of nutrients and oxygen to fetus. The high level of IL-10 has been reported in the intervillous space and could prevent the pathological effects. There is still no data of Th17 involvement in the pathogenesis of placental malaria. This study was conducted to reveal the influence of placental IL-17 and IL-10 levels on fetal weights in malaria placenta. Seventeen pregnant BALB/C mice were divided into control (8 pregnant mice) and treatment group (9 pregnant mice infected by Plasmodium berghei). Placental specimens stained with hematoxylin and eosin were examined to determine the level of cytoadherence by counting the infected erythrocytes in the intervillous space of placenta. Levels of IL-17 and IL-10 in the placenta were measured using ELISA. All fetuses were weighed by analytical balance. Statistical analysis using Structural Equation Modeling showed that cytoadherence caused an increased level of placental IL-17 and a decreased level of placental IL-10. Cytoadherence also caused low fetal weight. The increased level of placental IL-17 caused low fetal weight, and interestingly low fetal weight was caused by a decrease of placental IL-10. It can be concluded that low fetal weight in placental malaria is directly caused by sequestration of the parasites and indirectly by the local imbalance of IL-17 and IL-10 levels.

The role of environmental factors in modulating immune responses in early life

The concept of immunological memory stipulates that past exposures shape present immune function. These exposures include not only specific antigens impacting adaptive immune memory but also conserved pathogen or danger associated molecular patterns that mold innate immune responses for prolonged periods of time. It should thus not come as a surprise that there is a vast range of external or environmental factors that impact immunity. The importance of environmental factors modulating immunity is most readily recognized in early life, a period of rapidly changing environments. We here summarize available data on the role of environment shaping immune development and from it derive an overarching hypothesis relating the underlying molecular mechanisms and evolutionary principles involved.

Community-based scheduled screening and treatment of malaria in pregnancy for improved maternal and infant health in The Gambia, Burkina Faso and Benin: study protocol for a randomized controlled trial

Background

In sub-Saharan Africa, malaria continues to cause over 10,000 maternal deaths and 75,000 to 200,000 infant deaths. Successful control of malaria in pregnancy could save lives of mothers and babies and is an essential part of antenatal care in endemic areas. The primary objective is to determine the protective efficacy of community-scheduled screening and treatment (CSST) using community health workers (CHW) against the primary outcome of prevalence of placental malaria. The secondary objectives are to determine the protective efficacy of CSST on maternal anaemia, maternal peripheral infection, low birth weight, selection of sulfadoxine-pyrimethamine (SP) resistance markers, and on antenatal clinic (ANC) attendance and coverage of intermittent preventive treatment during pregnancy (IPTp-SP).

Methods/design

This is a multi-centre cluster-randomised controlled trial involving three countries with varying malaria endemicity; low (The Gambia) versus high transmission (Burkina Faso and Benin), and varying degrees of SP resistance (high in Benin and moderate in Gambia and Burkina Faso). CHW and their related catchment population who are randomised into the intervention arm will receive specific training on community-based case management of malaria in pregnancy. All women in both study arms will be enrolled at their first ANC visits in their second trimester where they will receive their first dose of IPTp-SP. Thereafter, CHW in the intervention arm will perform scheduled monthly screening and treatment in the womens homes. At time of delivery, a placental biopsy will be collected from all women to determine placental malaria. At each contact point, filter paper and blood slides will be collected for detection of malaria infection and SP resistance markers.

Discussion

To reach successful global malaria control, there is an urgent need to access those at greatest risk of malaria infection. The project is designed to develop a low-cost intervention in pregnant women which will have an immediate impact on the malaria burden in resource-limited countries. This will be done by adding to the standard IPTp-SP delivered through the health facilities: an “extension” strategy to the communities in rural areas thus bringing health services closer to where women live.

Trial registration

Current Controlled Trials: ISRCTN37259296 (5 July 2013), and clinicaltrials.gov: NCT01941264 (10 September 2013).

Submicroscopic infections with Plasmodium falciparum during pregnancy and their association with circulating cytokine, chemokine, and cellular profiles

The immunological consequences of pregnancy-associated malaria (PAM) due to Plasmodium falciparum have been extensively investigated in cross-sectional studies conducted at delivery, but there have been very few longitudinal studies of changes due to PAM during pregnancy. We conducted a prospective study in Benin to investigate the changes associated with PAM in groups of 131 and 111 women at inclusion in the second trimester and at delivery, respectively. Infected women were identified by standard microscopic examinations of blood smears and by quantitative PCR (qPCR) assays and were matched to uninfected control women by age, gestational age, and gravidity. We quantified plasma levels of a panel of soluble immunological mediators and other mediators, as well as the frequencies of peripheral blood mononuclear cell types. Comparisons of these variables in infected and uninfected women used multivariate analyses, and we also assessed the predictive value of variables measured at inclusion for pregnancy outcomes at delivery. In multivariate analyses, peripheral plasma interleukin 10 (IL-10) and gamma interferon-inducible protein 10 (IP-10) levels were associated with PAM at inclusion and at delivery, while higher IL-10 levels distinguished qPCR-detectable submicroscopic infections at inclusion but not at delivery. Maternal anemia at delivery was associated with markers of proinflammatory (increased frequency of monocytes) and anti-inflammatory (increased IL-10 levels and increased activation of regulatory T cells) activity measured at inclusion. Elevated concentrations of IL-10 are associated with the majority of P. falciparum infections during pregnancy, but this marker alone does not identify all submicroscopic infections. Reliably identifying such occult infections will require more sensitive and specific methods.

A morphometric and histological study of placental malaria shows significant changes to villous architecture in both Plasmodium falciparum and Plasmodium vivax infection

BACKGROUND

Malaria in pregnancy remains a major health problem. Placental malaria infection may cause pathophysiological changes in pregnancy and result in morphological changes to placental villi. Quantitative histomorphological image analysis of placental biopsies was performed to compare placental villous architecture between active or treated placental malaria cases and controls.

METHODS

A total of 67 placentas were studied from three clinical groups: control patients who did not have malaria (n = 27), active (n = 14) and treated (n=26) malaria cases, including both Plasmodium falciparum and Plasmodium vivax infections. Image analysis of histological placental sections was performed using ImageJ software to measure the number and size (area) of terminal villi, perimeter measurement per villus and total perimeter per unit area, and number of capillaries per villus (vascularity). Histological features of placental malaria were scored and these results were correlated with malaria status and clinical outcomes.

RESULTS

Villous size correlated with vascularity (p <0.0001) but was inversely correlated with observed villi per unit area, (p = 0.0001). Significantly greater villous area and vascularity was observed in UK controls. Indices of histological malaria infection were significantly greater in active versus treated malaria cases. Active placental malaria cases showed significantly smaller villous area (p <0.0084), vascularity (p <0.0139) and perimeter (p <0.0006) than treated malaria cases or controls, but significantly more villi per unit area (p <0.0001). Villous size in treated malaria cases was significantly larger than active placental malaria cases (p <0.001) and similar to controls. There was a significant relationship between villous number and anaemia at the time of infection (p <0.0034), but not placental weight, birth weight or gestational age at delivery. No differences were found between histology or villous morphology comparing infections with P. falciparum or P. vivax.

CONCLUSIONS

These results imply that villous size, perimeter and vascularity are acutely decreased during active placental malaria, decreasing the surface area available for gas exchange per villus. However the increased number of villi per unit area offsets this change and persists after treatment. Histopathological and villous architectural changes may be reversed by early detection and appropriate anti-malarial treatment.

Impact of pregnancy-associated malaria on infant malaria infection in southern Benin

BACKGROUND

Infants of mothers with placental Plasmodium falciparum infections at delivery are themselves more susceptible to malaria attacks or to infection in early life.

METHODOLOGY/ PRINCIPAL FINDINGS

To assess the impact of either the timing or the number of pregnancy-associated malaria (PAM) infections on the incidence of parasitemia or malaria attacks in infancy, we followed 218 mothers through pregnancy (monthly visits) up to delivery and their infants from birth to 12 months of age (fortnightly visits), collecting detailed clinical and parasitological data. After adjustment on location, mother's age, birth season, bed net use, and placental malaria, infants born to a mother with PAM during the third trimester of pregnancy had a significantly increased risk of infection (OR [95% CI]: 4.2 [1.6; 10.5], p = 0.003) or of malaria attack (4.6 [1.7; 12.5], p = 0.003). PAM during the first and second trimesters had no such impact. Similarly significant results were found for the effect of the overall number of PAM episodes on the time to first parasitemia and first malaria attack (HR [95% CI]: 2.95 [1.58; 5.50], p = 0.001 and 3.19 [1.59; 6.38], p = 0.001) respectively.

CONCLUSIONS/ SIGNIFICANCE

This study highlights the importance of protecting newborns by preventing repeated episodes of PAM in their mothers.

A secreted Plasmodium falciparum kinase reveals a signature motif for classification of tyrosine kinase-like kinases

Thorough bioinformatic and phylogenetic analyses of Plasmodium falciparum tyrosine kinase-like kinase (TKL) sequences revealed a clear evolutionary relationship of PF3D7_1121300 (thereafter called PfTKL2) to the IL-1 receptor-associated kinase (IRAK)/receptor-like kinase (RLK)/Pelle protein family. We identified a novel conserved motif that is unique to this family, as well as an insertion whose length allows distribution of its members into two distinct subfamilies, in a way that matches exactly the dichotomy between 'Tube/Tube-like kinases' (TTLKs) and 'Pelle-like kinases' (PLKs) distinguished previously on the basis of features in accessory domains. The PfTKL2 protein is expressed ubiquitously in asexual blood stages and in gametocytes, and the recombinant enzyme displays kinase activity in vitro. The protein is exported to the host erythrocyte; furthermore, in accordance with data from a previous study of the extracellular proteome of Plasmodium-infected erythrocytes, we show that PfTKL2 is secreted into the culture medium. Considering the functions of other members of the RLK/Pelle family in immunity, and its secretion to the extracellular medium, we speculate that PfTKL2 functions may include an immunomodulatory role promoting parasite survival in the human host.

Prospects and Pitfalls of Pregnancy-Associated Malaria Vaccination Based on the Natural Immune Response to Plasmodium falciparum VAR2CSA-Expressing Parasites

Pregnancy-associated malaria, a manifestation of severe malaria, is the cause of up to 200,000 infant deaths a year, through the effects of placental insufficiency leading to growth restriction and preterm delivery. Development of a vaccine is one strategy for control. Plasmodium falciparum-infected red blood cells accumulate in the placenta through specific binding of pregnancy-associated parasite variants that express the VAR2CSA antigen to chondroitin sulphate A on the surface of syncytiotrophoblast cells. Parasite accumulation, accompanied by an inflammatory infiltrate, disrupts the cytokine balance of pregnancy with the potential to cause placental damage and compromise foetal growth. Multigravid women develop immunity towards VAR2CSA-expressing parasites in a gravidity-dependent manner which prevents unfavourable pregnancy outcomes. Although current vaccine design, targeting VAR2CSA antigens, has succeeded in inducing antibodies artificially, this candidate may not provide protection during the first trimester and may only protect those women living in areas endemic for malaria. It is concluded that while insufficient information about placental-parasite interactions is presently available to produce an effective vaccine, incremental progress is being made towards achieving this goal.