Chondroitin sulfate proteoglycan but not hyaluronic acid is the receptor for the adherence of Plasmodium falciparum-infected erythrocytes in human placenta, and infected red blood cell adherence up-regulates the receptor expression

Effect of Glycosaminoglycans on Cryptosporidium Oocyst Attachment and Excystation

Cryptosporidium causes severe gastrointestinal disease resulting from the ingestion of oocysts, followed by oocyst excystation in the small intestine and the release of infective sporozoites. An understudied strategy for Cryptosporidium inactivation is purposeful oocyst excystation, as sporozoites do not survive long in the environment. This study showed that C. parvum oocyst excystation was induced by direct contact with various glycosaminoglycans (GAGs), including heparin (Hep), chondroitin sulfate A (CSA), and hyaluronan (HA), assembled on polydopamine (PD)-functionalized surfaces. PD surfaces elicited 97.9 ± 3.6% oocyst attachment, with some of the attached oocysts partially (7.3 ± 1.3%) or fully (4.0 ± 0.6%) excysted after 4 days. The PD-GAG surfaces (GAG concentration = 2 mg/mL) elicited similarly high attachment (>97%) and higher oocyst excystation efficiencies after 4 days. The PD-Hep surfaces elicited the highest number of attached excysted oocysts (11.8 ± 0.63% partially excysted; 11.9 ± 0.49% fully excysted), and the PD-HA surfaces elicited the lowest (8.8 ± 2.1% partially excysted; 7.8 ± 1.2% fully excysted). Surface characterization revealed that the addition of GAGs to the PD surface changed both the surface roughness as well as the surface wettability. Treatment of oocysts with an enzyme that degraded the surface glycocalyx markedly reduced excystation (to <2%) of the oocysts attached to the PD and PD-GAG surfaces. These findings suggest that GAGs provide an important local signal for the excystation of C. parvum oocysts and that certain surface-expressed oocyst receptors are necessary for efficient excystation. These oocyst-receptor relationships may be useful in the design of functionalized surfaces for the purposeful inactivation of oocysts in the environment or in water treatment systems. IMPORTANCE Polydopamine surfaces functionalized with glycosaminoglycans were shown to facilitate the attachment and excystation of Cryptosporidium parvum oocysts. Our findings suggest that a surface-expressed receptor on the oocyst wall plays a key role in excystation, with glycosaminoglycans serving as ligands that trigger the initiation of the process. Future technologies and treatment strategies designed to promote premature excystation of oocysts will minimize the ingestion of sporozoites that initiate infection. Therefore, the results from this study have important implications for the protection of public health from waterborne cryptosporidiosis and may serve as a foundation for engineered surfaces designed to remove oocysts from surface waters or inactivate oocysts in water treatment systems.

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.

Contribution of Murine Models to the Study of Malaria During Pregnancy

Annually, many pregnancies occur in areas of Plasmodium spp. transmission, particularly in underdeveloped countries with widespread poverty. Estimations have suggested that several million women are at risk of developing malaria during pregnancy. In particular cases, systemic infection caused by Plasmodium spp. may extend to the placenta, dysregulating local homeostasis and promoting the onset of placental malaria; these processes are often associated with increased maternal and fetal mortality, intrauterine growth restriction, preterm delivery, and reduced birth weight. The endeavor to understand and characterize the mechanisms underlying disease onset and placental pathology face several ethical and logistical obstacles due to explicit difficulties in assessing human gestation and biological material. Consequently, the advent of murine experimental models for the study of malaria during pregnancy has substantially contributed to our understanding of this complex pathology. Herein, we summarize research conducted during recent decades using murine models of malaria during pregnancy and highlight the most relevant findings, as well as discuss similarities to humans and the translational capacity of achieved results.

Molecular Principles of Intrauterine Growth Restriction in Plasmodium Falciparum Infection

Malaria in pregnancy still constitutes a particular medical challenge in tropical and subtropical regions. Of the five Plasmodium species that are pathogenic to humans, infection with Plasmodium falciparum leads to fulminant progression of the disease with massive impact on pregnancy. Severe anemia of the mother, miscarriage, stillbirth, preterm delivery and intrauterine growth restriction (IUGR) with reduced birth weight are frequent complications that lead to more than 10,000 maternal and 200,000 perinatal deaths annually in sub-Saharan Africa alone. P. falciparum can adhere to the placenta via the expression of the surface antigen VAR2CSA, which leads to sequestration of infected erythrocytes in the intervillous space. This process induces a placental inflammation with involvement of immune cells and humoral factors. Especially, monocytes get activated and change the release of soluble mediators, including a variety of cytokines. This proinflammatory environment contributes to disorders of angiogenesis, blood flow, autophagy, and nutrient transport in the placenta and erythropoiesis. Collectively, they impair placental functions and, consequently, fetal growth. The discovery that women in endemic regions develop a certain immunity against VAR2CSA-expressing parasites with increasing number of pregnancies has redefined the understanding of malaria in pregnancy and offers strategies for the development of vaccines. The following review gives an overview of molecular processes in P. falciparum infection in pregnancy which may be involved in the development of IUGR.

Epidemiology, drug resistance, and pathophysiology of Plasmodium vivax malaria

Malaria, caused by the protozoan parasites of the genus Plasmodium, is a major health problem in many countries of the world. Five parasite species namely, Plasmodium falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi, cause malaria in humans. Of these, P. falciparum and P. vivax are the most prevalent and account for the majority of the global malaria cases. In most areas of Africa, P. vivax infection is essentially absent because of the inherited lack of Duffy antigen receptor for chemokines on the surface of red blood cells that is involved in the parasite invasion of erythrocytes. Therefore, in Africa, most malaria infections are by P. falciparum and the highest burden of P. vivax infection is in Southeast Asia and South America. Plasmodium falciparum is the most virulent and as such, it is responsible for the majority of malarial mortality, particularly in Africa. Although, P. vivax infection has long been considered to be benign, recent studies have reported life-threatening consequences, including acute respiratory distress syndrome, cerebral malaria, multi-organ failure, dyserythropoiesis and anaemia. Despite exhibiting low parasite biomass in infected people due to parasite's specificity to infect only reticulocytes, P. vivax infection triggers higher inflammatory responses and exacerbated clinical symptoms than P. falciparum, such as fever and chills. Another characteristic feature of P. vivax infection, compared to P. falciparum infection, is persistence of the parasite as dormant liver-stage hypnozoites, causing recurrent episodes of malaria. This review article summarizes the published information on P. vivax epidemiology, drug resistance and pathophysiology.

Antimalarial Activity of Orally Administered Curcumin Incorporated in Eudragit®-Containing Liposomes

Curcumin is an antimalarial compound easy to obtain and inexpensive, having shown little toxicity across a diverse population. However, the clinical use of this interesting polyphenol has been hampered by its poor oral absorption, extremely low aqueous solubility and rapid metabolism. In this study, we have used the anionic copolymer Eudragit® S100 to assemble liposomes incorporating curcumin and containing either hyaluronan (Eudragit-hyaluronan liposomes) or the water-soluble dextrin Nutriose® FM06 (Eudragit-nutriosomes). Upon oral administration of the rehydrated freeze-dried nanosystems administered at 25/75 mg curcumin·kg−1·day−1, only Eudragit-nutriosomes improved the in vivo antimalarial activity of curcumin in a dose-dependent manner, by enhancing the survival of all Plasmodium yoelii-infected mice up to 11/11 days, as compared to 6/7 days upon administration of an equal dose of the free compound. On the other hand, animals treated with curcumin incorporated in Eudragit-hyaluronan liposomes did not live longer than the controls, a result consistent with the lower stability of this formulation after reconstitution. Polymer-lipid nanovesicles hold promise for their development into systems for the oral delivery of curcumin-based antimalarial therapies.

Malaria in pregnancy: the relevance of animal models for vaccine development

Malaria during pregnancy due to Plasmodium falciparum or P. vivax is a major public health problem in endemic areas, with P. falciparum causing the greatest burden of disease. Increasing resistance of parasites and mosquitoes to existing tools, such as preventive antimalarial treatments and insecticide-treated bed nets respectively, is eroding the partial protection that they offer to pregnant women. Thus, development of effective vaccines against malaria during pregnancy is an urgent priority. Relevant animal models that recapitulate key features of the pathophysiology and immunology of malaria in pregnant women could be used to accelerate vaccine development. This review summarizes available rodent and nonhuman primate models of malaria in pregnancy, and discusses their suitability for studies of biologics intended to prevent or treat malaria in this vulnerable population.

Combating malaria with nanotechnology-based targeted and combinatorial drug delivery strategies

Despite the advancement of science, infectious diseases such as malaria remain an ongoing challenge globally. The main reason this disease still remains a menace in many countries around the world is the development of resistance to many of the currently available anti-malarial drugs. While developing new drugs is rather expensive and the prospect of a potent vaccine is still evading our dream of a malaria-free world, one of the feasible options is to package the older drugs in newer ways. For this, nano-sized drug delivery vehicles have been used and are proving to be promising prospects in the way malaria will be treated in the future. Since, monotherapy has given way to combination therapy in malaria treatment, nanotechnology-based delivery carriers enable to encapsulate various drug moieties in the same package, thus avoiding the complications involved in conjugation chemistry to produce hybrid drug molecules. Further, we envisage that using targeted delivery approaches, we may be able to achieve a much better radical cure and curb the side effects associated with the existing drug molecules. Thus, this review will focus on some of the nanotechnology-based combination and targeted therapies and will discuss the possibilities of better therapies that may be developed in the future.

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.

Pre-clinical and clinical development of the first placental malaria vaccine

INTRODUCTION

Malaria during pregnancy is a massive health problem in endemic areas. Placental malaria infections caused by Plasmodium falciparum are responsible for up to one million babies being born with a low birth weight every year. Significant efforts have been invested into preventing the condition. Areas covered: Pub Med was searched using the broad terms 'malaria parasite placenta' to identify studies of interactions between parasite and host, 'prevention of placental malaria' to identify current strategies to prevent placental malaria, and 'placental malaria vaccine' to identify pre-clinical vaccine development. However, all papers from these searches were not systematically included. Expert commentary: The first phase I clinical trials of vaccines are well underway. Trials testing efficacy are more complicated to carry out as only women that are exposed to parasites during pregnancy will contribute to endpoint measurements, further it may require extensive follow-up to establish protection. Future second generation vaccines may overcome the inherent challenges in making an effective placental malaria vaccine.

Glycosaminoglycans and infection

Glycosaminoglycans (GAGs) are complex linear polysaccharides expressed in intracellular compartments, at the cell surface, and in the extracellular environment where they interact with various molecules to regulate many cellular processes implicated in health and disease. Subversion of GAGs is a pathogenic strategy shared by a wide variety of microbial pathogens, including viruses, bacteria, parasites, and fungi. Pathogens use GAGs at virtually every major portals of entry to promote their attachment and invasion of host cells, movement from one cell to another, and to protect themselves from immune attack. Pathogens co-opt fundamental activities of GAGs to accomplish these tasks. This ingenious strategy to subvert essential activities of GAGs likely prevented host organisms from deleting or inactivating these mechanisms during their evolution. The goal of this review is to provide a mechanistic overview of our current understanding of how microbes subvert GAGs at major steps of pathogenesis, using select GAG-pathogen interactions as representative examples.

Impact of placental Plasmodium falciparum malaria on the profile of some oxidative stress biomarkers in women living in Yaoundé, Cameroon

Background

Impact of the pathophysiology of Plasmodium falciparum placental malaria (PM) on the profile of some oxidative stress biomarkers and their relationship with poor pregnancy outcomes in women remain unknown.

Methods

Between 2013 and 2014, peripheral blood and placenta tissue from 120 Cameroonian women at delivery were assessed for maternal haemoglobin and, parasitaemia respectively. Parasite accumulation in the placenta was investigated histologically. The levels of oxidative stress biomarkers Malondialdehyde (MDA), Nitric Oxide (NO), Superoxide dismutase (SOD), Catalase (CAT) and Gluthatione (GSH) in the supernatant of teased placenta tissues were determined by Colorimetric enzymatic assays.

Results

Parasitaemia was inversely related to haemoglobin levels and birth weight (P <0.001 and 0.012, respectively). The level of lipid peroxide product (MDA) was significantly higher in the malaria infected (P = 0.0047) and anaemic (P = 0.024) women compared to their non-infected and non-anaemic counterparts, respectively. A similar trend was observed with SOD levels, though not significant. The levels of MDA also correlated positively with parasitaemia (P = 0.0024) but negatively with haemoglobin levels (P = 0.002). There was no association between parasitaemia, haemoglobin level and the other oxidative stress biomarkers. From histological studies, levels of MDA associated positively and significantly with placenta malaria infection and the presence of malaria pigments. The levels of SOD, NO and CAT increased with decreasing leukocyte accumulation in the intervillous space. Baby birth weight increased significantly with SOD and CAT levels, but decreased with levels of GSH.

Conclusions

Placental P. falciparum infection may cause oxidative stress of the placenta tissue with MDA as a potential biomarker of PM, which alongside GSH could lead to poor pregnancy outcomes (anaemia and low birth weight). This finding contributes to the understanding of the pathophysiology of P. falciparum placental malaria in women.

Placental malaria and modulation of immune and hormonal responses in Cameroonian women

Adverse pregnancy outcomes place the lives of mother and new born babies in jeopardy, especially in Sub Saharan Africa. Although a well-balanced network of the pregnancy-associated hormones and lipid fractions is necessary for healthy pregnancy, the profiles of some of these biomarkers alongside those of some cytokines in relation to placental malaria (PM) and poor pregnancy outcomes are unknown. Therefore between 2013 and 2014, paired peripheral and placental blood samples were collected from 135 Cameroonian women at delivery. Parasitaemia was determined microscopically and haemoglobin levels using Coulter counter. Plasma levels of cytokines (IFN-γ, IL-1β and IL-7) and pregnancy-associated hormones (17β oestradiol and progesterone) were measured by ELISA and the levels of lipid fractions: total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglycerides (TG) determined by Colorimetric enzymatic methods. Parasitaemia was inversely related to parity, haemoglobin levels and birth weight (P≤0.019). While the levels of IFN-γ and cholesterol (total, HDL and LDL) were higher in peripheral plasma, those of IL-1β, 17β oestradiol, progesterone and triglyceride were higher in placental blood (P<0.001). Absence of PM was significantly associated with high plasma levels of IFN-γ, IL-7 and HDL-C and low plasma levels of 17β oestradiol and TG. Moreover, IL-7 levels correlated positively and significantly with haemoglobin levels and with both peripheral and placental levels of progesterone. Baby birth weight increased with plasma levels of progesterone and HDL-C. Levels of IFN-γ correlated positively and significantly with HDL-C, but negatively with LDL-C; thus, might prevent pregnant women from atherogenic risk. Study of the inter-relationship between hormones, cytokines and lipids revealed that the association between IL-7 and progesterone and/or some lipid fractions followed inverse trends from that of IFN-γ. These results suggest that in PM, IFN-γ and IL-7 might protect against poor pregnancy outcomes, which decrease plasma levels of progesterone, maternal haemoglobin and HDL-C, leading to low birth weight. However, these cytokines may act differently with regards to progesterone and some lipid fractions. PM may also lower plasma levels of HDL-C and increase that of TG which is the most important risk factor for cardiovascular disorders and consequently poor pregnancy outcomes.

Role of some biomarkers in placental malaria in women living in Yaoundé, Cameroon

Despite intensive research on the immunpathology of placental malaria (PM), the role of some β-chemokines known to attract inflammatory cells is less known. This study sought to determine the role of CXCL-10, IL-10, IL-19, IL-17A and IL-23 in placental malaria in women at delivery. Between 2010 and 2011, paired peripheral and placental blood specimens were collected from 139 Cameroonian women at delivery. Differential white blood cell counts and malaria parasitaemia were determined microscopically while the accumulation of parasites in the placenta was investigated through histological studies. Plasma levels of CXCL-10, IL-10, IL-17A, IL-19 and Il-23 were determined by ELISA. The cytokines IL-10, IL-17A and IL-23 were predominant in peripheral plasma from both infected and non-infected women. While IL-10 associated negatively with parity, IL-23 showed a positive correlation (p<0.05). The production of CXCL-10 was independent of parity and higher in placental plasma. There was an association between the plasma levels of IL-10 and CXCL-10 with malaria parasitaemia in the placenta impression smears, placental and peripheral blood and the presence of malaria pigments in the placenta tissue. Leukocyte accumulation into the intervillous space correlated positively with plasma levels of placental IL-17A (p<0.001). Parity also associated with peripheral IL-17A (p=0.016). The peripheral and placental plasma levels of CXCL-10 and IL-10 also correlated positively with monocyte counts (p=0.011-0.042) while a negative correlation was found with lymphocyte counts (p=0.017 to <0.001) of the impression smear. However, the levels of IL-10 in both peripheral and placental plasma and CXCL-10 in placental plasma only, were higher in low birth weight baby. With regards to IL-17A, its placental plasma level correlated positively with lymphocyte counts of placental blood (p=0.045). During PM, CXCL-10 might attract monocytes and lymphocytes into the placenta where they produce inflammatory cytokines such as IL-10 and IL-17A to modulate the disease, which affect baby weight.

B-cell responses to pregnancy-restricted and -unrestricted Plasmodium falciparum erythrocyte membrane protein 1 antigens in Ghanaian women naturally exposed to malaria parasites

Protective immunity to Plasmodium falciparum malaria acquired after natural exposure is largely antibody mediated. IgG-specific P. falciparum EMP1 (PfEMP1) proteins on the infected erythrocyte surface are particularly important. The transient antibody responses and the slowly acquired protective immunity probably reflect the clonal antigenic variation and allelic polymorphism of PfEMP1. However, it is likely that other immune-evasive mechanisms are also involved, such as interference with formation and maintenance of immunological memory. We measured PfEMP1-specific antibody levels by enzyme-linked immunosorbent assay (ELISA) and memory B-cell frequencies by enzyme-linked immunosorbent spot (ELISPOT) assay in a cohort of P. falciparum-exposed nonpregnant Ghanaian women. The antigens used were a VAR2CSA-type PfEMP1 (IT4VAR04) with expression restricted to parasites infecting the placenta, as well as two commonly recognized PfEMP1 proteins (HB3VAR06 and IT4VAR60) implicated in rosetting and not pregnancy restricted. This enabled, for the first time, a direct comparison in the same individuals of immune responses specific for a clinically important parasite antigen expressed only during well-defined periods (pregnancy) to responses specific for comparable antigens expressed independent of pregnancy. Our data indicate that PfEMP1-specific B-cell memory is adequately acquired even when antigen exposure is infrequent (e.g., VAR2CSA-type PfEMP1). Furthermore, immunological memory specific for VAR2CSA-type PfEMP1 can be maintained for many years without antigen reexposure and after circulating antigen-specific IgG has disappeared. The study provides evidence that natural exposure to P. falciparum leads to formation of durable B-cell immunity to clinically important PfEMP1 antigens. This has encouraging implications for current efforts to develop PfEMP1-based vaccines.

CD36 contributes to malaria parasite-induced pro-inflammatory cytokine production and NK and T cell activation by dendritic cells

The scavenger receptor CD36 plays important roles in malaria, including the sequestration of parasite-infected erythrocytes in microvascular capillaries, control of parasitemia through phagocytic clearance by macrophages, and immunity. Although the role of CD36 in the parasite sequestration and clearance has been extensively studied, how and to what extent CD36 contributes to malaria immunity remains poorly understood. In this study, to determine the role of CD36 in malaria immunity, we assessed the internalization of CD36-adherent and CD36-nonadherent Plasmodium falciparum-infected red blood cells (IRBCs) and production of pro-inflammatory cytokines by DCs, and the ability of DCs to activate NK, and T cells. Human DCs treated with anti-CD36 antibody and CD36 deficient murine DCs internalized lower levels of CD36-adherent IRBCs and produced significantly decreased levels of pro-inflammatory cytokines compared to untreated human DCs and wild type mouse DCs, respectively. Consistent with these results, wild type murine DCs internalized lower levels of CD36-nonadherent IRBCs and produced decreased levels of pro-inflammatory cytokines than wild type DCs treated with CD36-adherent IRBCs. Further, the cytokine production by NK and T cells activated by IRBC-internalized DCs was significantly dependent on CD36. Thus, our results demonstrate that CD36 contributes significantly to the uptake of IRBCs and pro-inflammatory cytokine responses by DCs, and the ability of DCs to activate NK and T cells to produce IFN-γ. Given that DCs respond to malaria parasites very early during infection and influence development of immunity, and that CD36 contributes substantially to the cytokine production by DCs, NK and T cells, our results suggest that CD36 plays an important role in immunity to malaria. Furthermore, since the contribution of CD36 is particularly evident at low doses of infected erythrocytes, the results imply that the effect of CD36 on malaria immunity is imprinted early during infection when parasite load is low.

Histopathologies, immunolocalization, and a glycan binding screen provide insights into Plasmodium falciparum interactions with the human placenta

During pregnancy, Plasmodium falciparum-infected erythrocytes cytoadhere to the placenta. Infection is likely initiated at two sites where placental trophoblasts contact maternal blood: 1) via syncytiotrophoblast (STB), a multicellular transporting and biosynthetic layer that forms the surface of chorionic villi and lines the intervillous space, and 2) through invasive cytotrophoblasts, which line uterine vessels that divert blood to the placenta. Here, we investigated mechanisms of infected erythrocyte sequestration in relationship to the microanatomy of the maternal-fetal interface. Histological analyses revealed STB denudation in placental malaria, which brought the stromal cores of villi in direct contact with maternal blood. STB denudation was associated with hemozoin deposition (P = 0.01) and leukocyte infiltration (P = 0.001) and appeared to be a feature of chronic placental malaria. Immunolocalization of infected red blood cell receptors (CD36, ICAM1/CD54, and chondroitin sulfate A) in placentas from uncomplicated pregnancies showed that STB did not stain, while the underlying villous stroma was immunopositive. Invasive cytotrophoblasts expressed ICAM1. In malaria, STB denudation exposed CD36 and chondroitin sulfate A in the villous cores to maternal blood, and STB expressed ICAM1. Finally, we investigated infected erythrocyte adherence to novel receptors by screening an array of 377 glycans. Infected erythrocytes bound Lewis antigens that immunolocalized to STB. Our results suggest that P. falciparum interactions with STB-associated Lewis antigens could initiate placental malaria. Subsequent pathologies, which expose CD36, ICAM1, and chondroitin sulfate A, might propagate the infection.

Demonstration of specific binding of heparin to Plasmodium falciparum-infected vs. non-infected red blood cells by single-molecule force spectroscopy

Glycosaminoglycans (GAGs) play an important role in the sequestration of Plasmodium falciparum-infected red blood cells (pRBCs) in the microvascular endothelium of different tissues, as well as in the formation of small clusters (rosettes) between infected and non-infected red blood cells (RBCs). Both sequestration and rosetting have been recognized as characteristic events in severe malaria. Here we have used heparin and pRBCs infected by the 3D7 strain of P. falciparum as a model to study GAG-pRBC interactions. Fluorescence microscopy and fluorescence-assisted cell sorting assays have shown that exogenously added heparin has binding specificity for pRBCs (preferentially for those infected with late forms of the parasite) vs. RBCs. Heparin-pRBC adhesion has been probed by single-molecule force spectroscopy, obtaining an average binding force ranging between 28 and 46 pN depending on the loading rate. No significant binding of heparin to non-infected RBCs has been observed in control experiments. This work represents the first approach to quantitatively evaluate GAG-pRBC molecular interactions at the individual molecule level.

Recent advances and perspectives on tropical diseases: Malaria

Malaria remains a major health problem in the world. It is a neglected disease because it occurs almost exclusively in poor developing countries, which offer negligible marketable and profitable opportunities. Malaria (together with Tuberculosis), is responsible for an unprecedented global health crisis with devastating effects in developing countries. The 2011 Word Malaria Report indicated that 106 countries showed endemic malaria. Malaria control depends mainly on drug treatment, which is increasingly difficult due to the spread of drug resistant parasites and requires expensive drug combinations. Part of the inability to combat this disease is attributed to an incomplete understanding of its pathogenesis and pathophysiology. Improving the knowledge of the underlying pathogenic mechanisms of malaria transmission and of the exclusive metabolic pathways of the parasites (protozoa of the genus Plasmodium), should promote efficient treatment of disease and help the identification of novel targets for potential therapeutic interventions. Moreover, the elucidation of determinants involved in the spread of malaria will provide important information for efficient planning of strategies for targeted control.

Fetal and maternal hemodynamics in acute malaria during pregnancy

OBJECTIVE

To measure maternal and fetal hemodynamics during acute malaria in pregnancy.

METHODS

Time courses of maternal heart rate (MHR), maternal blood pressure (BP), and fetal heart rate (FHR) were performed until 56 days after initiation of anti-malarial treatment with artemether-lumefantrine. Women with malaria were hospitalized for at least 3 days until recovery.

RESULTS

Mean baseline characteristics of pregnant women with malaria (n=38) versus pregnant women without malaria (n=39) were as follows: gestational age (28.8 vs 24.6 weeks; P=0.006); maximum FHR (165.3 vs 158.3 beats per minute [bpm]; P=0.054); minimum FHR (137.6 vs 128.7 bpm; P=0.016); mean BP (74.7 vs 80.9 mm Hg; P=0.001); pulse pressure (40.3 vs 42.1mm Hg; P=0.300); and MHR (107.4 vs 81.3 bpm; P<0.001). The geometric mean parasite count was 13 795 per μL. Complete time courses were collected from a subgroup of participants. For women with malaria, maternal body temperature and BP normalized within 24 hours and after 72 hours, respectively. The MHR among pregnant women without malaria showed a physiologic increase during pregnancy of approximately 7 bpm between days 0 and 56. The mean FHR among women with malaria normalized after 72 hours.

CONCLUSION

Acute malaria induces maternal and fetal hemodynamic changes.

The case for PfEMP1-based vaccines to protect pregnant women against Plasmodium falciparum malaria

Vaccines are very cost-effective tools in combating infectious disease mortality and morbidity. Unfortunately, vaccines efficiently protecting against infection with malaria parasites are not available and are not likely to appear in the near future. An alternative strategy would be vaccines protecting against the disease and its consequences rather than against infection per se, by accelerating the development of the protective immunity that is normally acquired after years of exposure to malaria parasites in areas of stable transmission. This latter strategy is being energetically pursued to develop a vaccine protecting pregnant women and their offspring against mortality and morbidity caused by the accumulation of Plasmodium falciparum-infected erythrocytes in the placenta. It is based on a detailed understanding of the parasite antigen and the host receptor involved in this accumulation, as well as knowledge regarding the protective immune response that is acquired in response to placental P. falciparum infection. Nevertheless, it remains controversial in some quarters whether such a vaccine would have the desired impact, or indeed whether the strategy is meaningful. This article critically examines the relevance of several perceived obstacles to development of a vaccine against placental malaria.

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.

How specific is Plasmodium falciparum adherence to chondroitin 4-sulfate?

Plasmodium falciparum infection during pregnancy results in the sequestration of infected red blood cells (IRBCs) in the placenta, contributing to pregnancy associated malaria (PAM). IRBC adherence is mediated by the binding of a variant Plasmodium falciparum erythrocyte binding protein 1 named VAR2CSA to the low sulfated chondroitin 4-sulfate (C4S) proteoglycan (CSPG) present predominantly in the intervillous space of the placenta. IRBC binding is highly specific to the level and distribution of 4-sulfate groups in C4S. Given the strict specificity of IRBC-C4S interactions, it is better to use either placental CSPG or CSPGs bearing structurally similar C4S chains in defining VAR2CSA structural architecture that interact with C4S, evaluating VAR2CSA constructs for vaccine development or studying structure-based inhibitors as therapeutics for PAM.

Development of a novel ex vivo model of corneal fungal adherence

PURPOSE

To construct a suitable ex vivo model for the research of molecular mechanisms and the pharmacological screening of fungal adherence on the corneal surface.

MATERIALS AND METHODS

Mouse eyes were divided into three groups as follows: a control group with normal corneal epithelium, a group with corneal epithelium that was needle-scarified, and a group with corneal epithelium that was completely debrided. All 96 corneas were placed in organ culture and inoculated with 5 μl spore suspensions of Candida albicans at 10⁹, 10⁸, or 10⁷ colony-forming units (CFU)/ml and incubated for 0, 30, 60, or 120 min. The corneas were homogenated and diluted for quantification by counting the CFU. The effects of amphotericin B or chondroitin sulfate on the adherence of the fungal spores were evaluated with the ex vivo organ culture model and were also compared with the human corneal epithelium monolayer model in vitro.

RESULTS

Compared with the normal corneas with intact epithelium, the corneas with scarified and debrided epithelium adhered more spores for above two and four folds. The spore adhesion on the corneal surface was in an inoculation concentration- and incubation time-dependent manner. Moreover, both amphotericin B and chondroitin sulfate inhibited the adhesion of C. albicans spores on the corneal surface, but the inhibitory rates were different between the ex vivo corneal organ culture model and the in vitro corneal epithelium monolayer model.

CONCLUSIONS

The corneal organ culture was a suitable ex vivo model for the research of fungal adhesion mechanisms and drug screening.

Efficacy of intermittent preventive treatment with sulfadoxine-pyrimethamine on placental parasitemia in pregnant women in midwestern Nigeria

OBJECTIVE

To assess the effect of intermittent preventive treatment with sulfadoxine and pyrimethamine (IPT-SP) on placental parasitemia and maternal and perinatal outcome.

METHODS

We compared placental malaria parasitemia during pregnancy and pregnancy outcome in 2 groups of women receiving antenatal care at University of Benin Teaching Hospital. One group was prophylactically treated with IPT-SP and the other was not treated.

RESULTS

The parasitemia rates for peripheral, placental, and cord blood were 11.9%, 11.4%, and 2.7% in the IPT-SP group (n=370) and 19.1%, 22.6%, and 6.2% in the control group (n=371) (P=0.006, P=0.002, and P=0.02, respectively). The treatment reduced the odds of placental parasitemia by 37% (OR 0.63; 95% CI, 0.48-0.81). Peripheral (P=0.002) and placental (P=0.001) parasitemia were significantly reduced in the subgroup of women who took 2 or 3 doses of SP. Fewer women (16.2%) in the IPT-SP group than the control group (23.7%) had symptomatic malaria. Anemia at delivery was significantly lower in the IPT-SP group (10.8 vs 1.6%). The risks of abortion, preterm delivery, and low birth weight were also significantly lower in the IPT-SP group.

CONCLUSION

IPT-SP is effective in preventing placental parasitemia, and reduces rates of malaria, maternal anemia, abortion, preterm delivery and low birth weight among pregnant women.

Molecular interactions in the placenta during malaria infection

Placental malaria is the placental sequestration of Plasmodium falciparum infected erythrocytes that accumulate in the intervillous space, resulting in pathological alterations. The intervillous space, the main compartment for exchange of nutrients and delivery of oxygen to the fetus, is of utmost importance for fetal development. Events leading to adverse outcomes of placental malaria can be summarized in four steps: (1) accumulation of P. falciparum infected erythrocytes; (2) infiltration of monocytes and macrophages; (3) alteration of the placental cytokine balance and (4) pathogenesis of adverse pregnancy outcomes. These events are triggered by chemokines and cytokines leading to impaired materno-fetal exchange and damage to the placenta. This review describes the events during placental malaria infection at molecular level and presents a simplified model describing all crucial steps leading to adverse pregnancy outcomes based on a review of recent literature (August 2009).

Of mice and women: rodent models of placental malaria

Pregnant women are at increased malaria risk. The infections are characterized by placental accumulation of infected erythrocytes (IEs) with adverse consequences for mother and baby. Placental IE sequestration in the intervillous space is mediated by variant surface antigens (VSAs) selectively expressed in placental malaria (PM) and specific for chondroitin sulfate A (CSA). In Plasmodium falciparum, these VSA(PM) appear largely synonymous with the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family variant VAR2CSA. As rodent malaria parasites do not possess PfEMP1 homologs, the usefulness of experimental mouse PM models remains controversial. However, many features of murine and human PM are similar, including involvement of VSAs analogous to PfEMP1. It thus appears that rodent model studies can further the understanding of VSA-dependent malaria pathogenesis and immunity.

Peripheral T cells derived from Alzheimer's disease patients overexpress CXCR2 contributing to its transendothelial migration, which is microglial TNF-alpha-dependent

The mechanism of circulating T cells entry into the brain in Alzheimer's diseases (AD) remains unclear. Here, we showed that peripheral T cells derived from AD patients overexpress CXCR2 to enhance its transendothelial migration. T cells migration through in vitro blood-brain barrier model was effectively blocked by anti-CXCR2 antibody or IL-8 (a CXCR2 ligand) RNAi in human brain microvascular endothelial cells (HBMECs). Amyloid beta (Abeta) injection in rat hippocampus upregulated CXCR2 expression accompanied with increased T cells occurrence in the brain, and this enhanced T cells entry was effectively blocked by CXCR2 antagonist. Furthermore, anti-TNF-alpha antibody blocked IL-8 production in HBMECs and T cells transendothelial migration caused by the culture supernatant of microglia treated with Abeta. Blockage of intracerebral TNF-alpha abolished the upregulation of CXCR2 in peripheral T cells and the increased T cells occurrence in the brain induced by Abeta injection in rat hippocampus. These data suggest that CXCR2 overexpression in peripheral T cells is intracerebral microglial TNF-alpha-dependent and TNF-alpha primes T cells transendothelial migration in Alzheimer's diseases.

Dysregulation of angiopoietins is associated with placental malaria and low birth weight

Background

Placental malaria (PM) is associated with adverse pregnancy outcomes including low birth weight (LBW). However, the precise mechanisms by which PM induces LBW are poorly defined. Based on the essential role of angiopoietin (ANG)-1 and -2 in normal placental vascular development, we hypothesized that PM may result in the dysregulation of angiopoietins and thereby contribute to LBW outcomes.

Methods and Findings

In a mouse model of PM, we show that Plasmodium berghei ANKA infection of pregnant mice resulted in dysregulated angiopoietin levels and fetal growth restriction. PM lead to decreased ANG-1, increased ANG-2, and an elevated ratio of ANG-2/ANG-1 in the placenta and the serum. These observations were extended to malaria-exposed pregnant women: In a study of primigravid women prospectively followed over the course of pregnancy, Plasmodium falciparum infection was associated with a decrease in maternal plasma ANG-1 levels (P = 0.031) and an increase in the ANG-2:ANG-1 ratio (P = 0.048). ANG-1 levels recovered with successful treatment of peripheral parasitemia (P = 0.010). In a cross-sectional study of primigravidae at delivery, angiopoietin dysregulation was associated with PM (P = 0.002) and LBW (P = 0.041). Women with PM who delivered LBW infants had increased ANG-2:ANG-1 ratios (P = 0.002) compared to uninfected women delivering normal birth weight infants.

Conclusions

These data support the hypothesis that dysregulation of angiopoietins is associated with PM and LBW outcomes, and suggest that ANG-1 and ANG-2 levels may be clinically informative biomarkers to identify P. falciparum-infected mothers at risk of LBW deliveries.

Proteoglycans in host-pathogen interactions: molecular mechanisms and therapeutic implications

Many microbial pathogens subvert proteoglycans for their adhesion to host tissues, invasion of host cells, infection of neighbouring cells, dissemination into the systemic circulation, and evasion of host defence mechanisms. Where studied, specific virulence factors mediate these proteoglycan-pathogen interactions, which are thus thought to affect the onset, progression and outcome of infection. Proteoglycans are composites of glycosaminoglycan (GAG) chains attached covalently to specific core proteins. Proteoglycans are expressed ubiquitously on the cell surface, in intracellular compartments, and in the extracellular matrix. GAGs mediate the majority of ligand-binding activities of proteoglycans, and many microbial pathogens elaborate cell-surface and secreted factors that interact with GAGs. Some pathogens also modulate the expression and function of proteoglycans through known virulence factors. Several GAG-binding pathogens can no longer attach to and invade host cells whose GAG expression has been reduced by mutagenesis or enzymatic treatment. Furthermore, GAG antagonists have been shown to inhibit microbial attachment and host cell entry in vitro and reduce virulence in vivo. Together, these observations underscore the biological significance of proteoglycan-pathogen interactions in infectious diseases.

Chloroquine reduces arylsulphatase B activity and increases chondroitin-4-sulphate: implications for mechanisms of action and resistance

BACKGROUND

The receptors for adhesion of Plasmodium falciparum-infected red blood cells (RBC) in the placenta have been identified as chondroitin-4-sulphate (C4S) proteoglycans, and the more sulphate-rich chondroitin oligosaccharides have been reported to inhibit adhesion. Since the anti-malarial drug chloroquine accumulates in lysosomes and alters normal lysosomal processes, the effects of chloroquine on the lysosomal enzyme arylsulphatase B (ASB, N-acetylgalactosamine-4-sulphatase), which removes 4-sulphate groups from chondroitin-4-sulphate, were addressed. The underlying hypothesis derived from the recognized impairment of attachment of parasite-infected erythrocytes in the placenta, when chondroitin-4-sulphation was increased. If chloroquine reduced ASB activity, leading to increased chondroitin-4-sulphation, it was hypothesized that the anti-malarial mechanism of chloroquine might derive, at least in part, from suppression of ASB.

METHODS

Experimental methods involved cell culture of human placental, bronchial epithelial, and cerebrovascular cells, and the in vitro exposure of the cells to chloroquine at increasing concentrations and durations. Measurements of arylsulphatase B enzymatic activity, total sulphated glycosaminoglycans (sGAG), and chondroitin-4-sulphate (C4S) were performed using in vitro assays, following exposure to chloroquine and in untreated cell preparations. Fluorescent immunostaining of ASB was performed to determine the effect of chloroquine on cellular ASB content and localization. Mass spectrometry and high performance liquid chromatography were performed to document and to quantify the changes in chondroitin disaccharides following chloroquine exposure.

RESULTS

In the human placental, bronchial epithelial, and cerebrovascular cells, exposure to increasing concentrations of chloroquine was associated with reduced ASB activity and with increased concentrations of sGAG, largely attributable to increased C4S. The study data demonstrated: 1) decline in ASB activity following chloroquine exposure; 2) inverse correlation between ASB activity and C4S content; 3) increased content of chondroitin-4-sulphate disaccharides following chloroquine exposure; and 4) decline in extent of chloroquine-induced ASB reduction with lower baseline ASB activity. Confocal microscopy demonstrated the presence of ASB along the cell periphery, indicating extra-lysosomal localization.

CONCLUSIONS

The study data indicate that the therapeutic mechanism of chloroquine action may be attributable, at least in part, to reduction of ASB activity, leading to increased chondroitin-4-sulphation in human placental, bronchial epithelial, and cerebrovascular cells. In vivo, increased chondroitin-4-sulphation may reduce the attachment of P. falciparum-infected erythrocytes to human cells. Extra-lysosomal localization of ASB and reduced impact of chloroquine when baseline ASB activity is less suggest possible mechanisms of resistance to the effects of chloroquine.

Recrudescent Plasmodium berghei from pregnant mice displays enhanced binding to the placenta and induces protection in multigravida

Pregnancy-associated malaria (PAM) is associated with placenta pathology and poor pregnancy outcome but the mechanisms that control the malaria parasite expansion in pregnancy are still poorly understood and not amenable for study in human subjects. Here, we used a set of new tools to re-visit an experimental mouse model of pregnancy-induced malaria recrudescence, BALB/c with chronic Plasmodium berghei infection. During pregnancy 60% of the pre-exposed primiparous females showed pregnancy-induced malaria recrudescence and we demonstrated that the recrudescent P. berghei show an unexpected enhancement of the adherence to placenta tissue sections with a marked specificity for CSA. Furthermore, we showed that the intensity of parasitemia in primigravida was quantitatively correlated with the degree of thickening of the placental tissue and up-regulation of inflammation-related genes such as IL10. We also confirmed that the incidence of pregnancy-induced recrudescence, the intensity of the parasitemia peak and the impact on the pregnancy outcome decreased gradually from the first to the third pregnancy. Interestingly, placenta pathology and fetal impairment were also observed at low frequency among non-recrudescent females. Together, the data raise the hypothesis that recrudescent P. berghei displays selected specificity for the placenta tissue enabling on one hand, the triggering of the pathological process underlying PAM and on the other hand, the induction of PAM protection mechanisms that are revealed in subsequent pregnancies. Thus, by exploiting P. berghei pregnancy-induced recrudescence, this experimental system offers a mouse model to study the susceptibility to PAM and the mechanisms of disease protection in multigravida.

Identification of glycosaminoglycan binding regions in the Plasmodium falciparum encoded placental sequestration ligand, VAR2CSA

BACKGROUND

Pregnancy malaria is caused by Plasmodium falciparum-infected erythrocytes binding the placental receptor chondroitin sulfate A (CSA). This results in accumulation of parasites in the placenta with severe clinical consequences for the mother and her unborn child. Women become resistant to placental malaria as antibodies are acquired which specifically target the surface of infected erythrocytes binding in the placenta. VAR2CSA is most likely the parasite-encoded protein which mediates binding to the placental receptor CSA. Several domains have been shown to bind CSA in vitro; and it is apparent that a VAR2CSA-based vaccine cannot accommodate all the CSA binding domains and serovariants. It is thus of high priority to define minimal ligand binding regions throughout the VAR2CSA molecule.

METHODS

To define minimal CSA-binding regions/peptides of VAR2CSA, a phage display library based on the entire var2csa coding region was constructed. This library was screened on immobilized CSA and cells expressing CSA resulting in a limited number of CSA-binding phages. Antibodies against these peptides were affinity purified and tested for reactivity against CSA-binding infected erythrocytes.

RESULTS

The most frequently identified phages expressed peptides residing in the parts of VAR2CSA previously defined as CSA binding. In addition, most of the binding regions mapped to surface-exposed parts of VAR2CSA. The binding of a DBL2X peptide to CSA was confirmed with a synthetic peptide. Antibodies against a CSA-binding DBL2X peptide reacted with the surface of infected erythrocytes indicating that this epitope is accessible for antibodies on native VAR2CSA on infected erythrocytes.

CONCLUSION

Short continuous regions of VAR2CSA with affinity for multiple types of CSA were defined. A number of these regions localize to CSA-binding domains and to surface-exposed regions within these domains and a synthetic peptide corresponding to a peptide sequence in DBL2 was shown to bind to CSA and not to CSC. It is likely that some of these epitopes are involved in native parasite CSA adhesion. However, antibodies directed against single epitopes did not inhibit parasite adhesion. This study supports phage display as a technique to identify CSA-binding regions of large proteins such as VAR2CSA.

Immunologic activation of human syncytiotrophoblast by Plasmodium falciparum

Background

Malaria during pregnancy is characterized by the sequestration of malaria-infected red blood cells (iRBC) in the intervillous spaces of the placenta, often accompanied by the infiltration of maternal mononuclear cells, causing substantial maternal and foetal/infant morbidity. The iRBC bind to receptors expressed by the syncytiotrophoblast (ST). How ST responds to this interaction remains poorly understood. Because it is known that ST is immunoactive and can respond to infectious agents, the consequences of this ST-iRBC interaction should be investigated.

Methods

An in vitro system was used to assess the biochemical and immunological changes induced in ST by ST-adherent iRBCs. Changes in ST mitogen-activated protein kinase (MAPK) activation were assessed by immunoblotting and mRNA expression levels of selected cytokine and chemokines in primary ST bound by iRBC were determined using real-time, reverse transcription PCR. In addition, secreted cytokine and chemokine proteins were assayed by standard ELISA, and chemotaxis of PBMC was assessed using a two-chamber assay system.

Results

Following iRBC/ST interaction, ST C-Jun N-terminal kinase 1 (JNK1) was activated and modest increases in the mRNA expression of TGF-β and IL-8/CXCL8 were observed. In addition, this interaction increased secretion of MIF and MIP-1α/CCL3 by ST and induced migration of PBMC towards iRBC-stimulated ST.

Conclusion

Results from this study provide the first evidence that ST participates in shaping the local immunological milieu and in the recruitment of maternal immune cells to the maternal blood space during placental malaria infection.

Pregnancy outcome and placenta pathology in Plasmodium berghei ANKA infected mice reproduce the pathogenesis of severe malaria in pregnant women

Pregnancy-associated malaria (PAM) is expressed in a range of clinical complications that include increased disease severity in pregnant women, decreased fetal viability, intra-uterine growth retardation, low birth weight and infant mortality. The physiopathology of malaria in pregnancy is difficult to scrutinize and attempts were made in the past to use animal models for pregnancy malaria studies. Here, we describe a comprehensive mouse experimental model that recapitulates many of the pathological and clinical features typical of human severe malaria in pregnancy. We used P. berghei ANKA-GFP infection during pregnancy to evoke a prominent inflammatory response in the placenta that entails CD11b mononuclear infiltration, up-regulation of MIP-1 alpha chemokine and is associated with marked reduction of placental vascular spaces. Placenta pathology was associated with decreased fetal viability, intra-uterine growth retardation, gross post-natal growth impairment and increased disease severity in pregnant females. Moreover, we provide evidence that CSA and HA, known to mediate P. falciparum adhesion to human placenta, are also involved in mouse placental malaria infection. We propose that reduction of maternal blood flow in the placenta is a key pathogenic factor in murine pregnancy malaria and we hypothesize that exacerbated innate inflammatory responses to Plasmodium infected red blood cells trigger severe placenta pathology. This experimental model provides an opportunity to identify cell and molecular components of severe PAM pathogenesis and to investigate the inflammatory response that leads to the observed fetal and placental blood circulation abnormalities.

Plasmodiumin the placenta: parasites, parity, protection, prevention and possibly preeclampsia

The epidemiology of pregnancy malaria infection and disease is complex but reflects underlying interactions between thePlasmodium falciparumparasite, the mother, and the foetus. Parasites sequester in the human placenta by binding to chondroitin sulfate A (CSA), a novel receptor that does not commonly support binding of other parasites. Women become resistant toP. falciparummalaria over successive pregnancies as they acquire antibodies against the CSA-binding placental parasite forms. Due to acquired immunity, placental malaria is briefer and less inflammatory in multigravid women than primigravid women, and these parity differences may account for the different outcomes these women and their offspring experience. Commonly recognized sequelae of malaria-like maternal anaemia and low birth weight primarily occur in first and second pregnancies. Hypertension may result from maternal-foetal conflict over the inflammatory response to placental malaria, and occurs in young, first-time mothers. Placental malaria can either increase or decrease parasitaemia risk in the offspring, depending on the mother's parity. The burden of disease due to pregnancy malaria, and the benefits of an effective vaccine, may be much greater than is currently appreciated.

Disruption of var2csa gene impairs placental malaria associated adhesion phenotype

Infection with Plasmodium falciparum during pregnancy is one of the major causes of malaria related morbidity and mortality in newborn and mothers. The complications of pregnancy-associated malaria result mainly from massive adhesion of Plasmodium falciparum-infected erythrocytes (IE) to chondroitin sulfate A (CSA) present in the placental intervillous blood spaces. Var2CSA, a member of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family is the predominant parasite ligand mediating CSA binding. However, experimental evidence suggests that other host receptors, such as hyaluronic acid (HA) and the neonatal Fc receptor, may also support placental binding. Here we used parasites in which var2csa was genetically disrupted to evaluate the contribution of these receptors to placental sequestration and to identify additional adhesion receptors that may be involved in pregnancy-associated malaria. By comparison to the wild-type parasites, the FCR3Δvar2csa mutants could not be selected for HA adhesion, indicating that var2csa is not only essential for IE cytoadhesion to the placental receptor CSA, but also to HA. However, further studies using different pure sources of HA revealed that the previously observed binding results from CSA contamination in the bovine vitreous humor HA preparation. To identify CSA-independent placental interactions, FCR3Δvar2csa mutant parasites were selected for adhesion to the human placental trophoblastic BeWo cell line. BeWo selected parasites revealed a multi-phenotypic adhesion population expressing multiple var genes. However, these parasites did not cytoadhere specifically to the syncytiotrophoblast lining of placental cryosections and were not recognized by sera from malaria-exposed women in a parity dependent manner, indicating that the surface molecules present on the surface of the BeWo selected population are not specifically expressed during the course of pregnancy-associated malaria. Taken together, these results demonstrate that the placental malaria associated phenotype can not be restored in FCR3Δvar2csa mutant parasites and highlight the key role of var2CSA in pregnancy malaria pathogenesis and for vaccine development.