Clinical features and pathogenesis of severe malaria

The acute phase response in children with mild and severe malaria in Papua New Guinea

The production of acute phase proteins during infection is an important part of innate immunity and limits inflammation. However, little is known of the acute phase response in malaria. We measured acute phase proteins in plasma in children attending clinics and admitted to hospital with acute malaria in Papua New Guinea. Plasma ferritin concentration increased progressively with disease severity with markedly elevated levels in the most severely ill children. Plasma ferritin was >500 ng/ml in 7/99 (7.1%) outpatients with uncomplicated malaria, 22/100 (22.0%) hospital non-severe cases, 64/175 (36.6%) severe malaria cases who survived and 7/9 (77.8%) severe malaria deaths (P<0.001). The greatest concentration of ferritin (3561 ng/ml) was observed in a child who died. By contrast, C-reactive protein concentration was markedly increased in 153 children with uncomplicated malaria [median 203 (interquartile range 51-365) microg/ml] but, surprisingly, was only moderately increased in 135 children with one or more severe manifestations of malaria [47 (17-97) microg/ml; P<0.001] and in 6 children who died [41 (22-280) microg/ml]. Excessive free-radical damage resulting from a combination of iron-induced oxidant stress and reduced levels of C-reactive protein may be an important pathological mechanism in severe malaria and amenable to therapeutic intervention.

Uric acid is a mediator of the Plasmodium falciparum-induced inflammatory response

Background

Malaria triggers a high inflammatory response in the host that mediates most of the associated pathologies and contributes to death. The identification of pro-inflammatory molecules derived from Plasmodium is essential to understand the mechanisms of pathogenesis and to develop targeted interventions. Uric acid derived from hypoxanthine accumulated in infected erythrocytes has been recently proposed as a mediator of inflammation in rodent malaria.

Methods and Findings

We found that human erythrocytes infected with Plasmodium falciparum gradually accumulate hypoxanthine in their late stages of development.

To analyze the role of hypoxanthine-derived uric acid induced by P. falciparum on the inflammatory cytokine response from human blood mononuclear cells, cultures were treated with allopurinol, to inhibit uric acid formation from hypoxanthine, or with uricase, to degrade uric acid. Both treatments significantly reduce the secretion of TNF, IL-6, IL-1β and IL-10 from human cells.

Conclusions and Significance

Uric acid is a major contributor of the inflammatory response triggered by P. falciparum in human peripheral blood mononuclear cells. Since the inflammatory reaction induced by P. falciparum is considered a major cause of malaria pathogenesis, identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease.

Multifunctional aspartic peptidase prosegments

The structure-function relationships of aspartic peptidases (APs) (EC 3.4.23.X) have been extensively investigated, yet much remains to be elucidated regarding the various molecular mechanisms of these enzymes. Over the past years, APs have received considerable interest for food applications (e.g. cheese, fermented foods) and as potential targets for pharmaceutical intervention in human diseases including hypertension, cancer, Alzheimer's disease, AIDS (acquired immune deficiency syndrome), and malaria. A deeper understanding of the structure and function of APs, therefore, will have a direct impact on the design of peptidase inhibitors developed to treat such diseases. Most APs are synthesized as zymogens which contain an N-terminal prosegment (PS) domain that is removed at acidic pH by proteolytic cleavage resulting in the active enzyme. While the nature of the AP PS function is not entirely understood, the PS can be important in processes such as the initiation of correct folding, protein stability, blockage of the active site, pH-dependence of activation, and intracellular sorting of the zymogen. This review summarizes the current knowledge of AP PS function (especially within the A1 family), with particular emphasis on protein folding, cellular sorting, and inhibition.

Structural interactions in chondroitin 4-sulfate mediated adherence of Plasmodium falciparum infected erythrocytes in human placenta during pregnancy-associated malaria

Infection with Plasmodium falciparum during pregnancy results in the adherence of infected red blood cells (IRBCs) in placenta, causing pregnancy-associated malaria with severe health complications in mothers and fetuses. The chondroitin 4-sulfate (C4S) chains of very low sulfated chondroitin sulfate proteoglycans (CSPGs) in placenta mediate the IRBC adherence. While it is known that partially sulfated but not fully sulfated C4S effectively binds IRBCs, structural interactions involved remain unclear and are incompletely understood. In this study, structurally defined C4S oligosaccharides of varying sulfate contents and sizes were evaluated for their ability to inhibit the binding of IRBCs from different P. falciparum strains to CSPG purified from placenta. The results clearly show that, with all parasite strains studied, dodecasaccharide is the minimal chain length required for the efficient adherence of IRBCs to CSPG and two 4-sulfated disaccharides within this minimal structural motif are sufficient for maximal binding. Together, these data demonstrate for the first time that the C4S structural requirement for IRBC adherence is parasite strain-independent. We also show that the carboxyl group on nonreducing end glucuronic acid in dodecasaccharide motif is important for IRBC binding. Thus, in oligosaccharides containing terminal 4,5-unsaturated glucuronic acid, the nonreducing end disaccharide moiety does not interact with IRBCs due to the altered spatial orientation of carboxyl group. In such C4S oligosaccharides, 14-mer but not 12-mer constitutes the minimal motif for inhibition of IRBC binding to placental CSPG. These data have important implications for the development and evaluation of therapeutics and vaccine for placental malaria.

Host-parasite interactions revealed by Plasmodium falciparum metabolomics

Intracellular pathogens have devised mechanisms to exploit their host cells to ensure their survival and replication. The malaria parasite Plasmodium falciparum relies on an exchange of metabolites with the host for proliferation. Here we describe a mass spectrometry-based metabolomic analysis of the parasite throughout its 48 hr intraerythrocytic developmental cycle. Our results reveal a general modulation of metabolite levels by the parasite, with numerous metabolites varying in phase with the developmental cycle. Others differed from uninfected cells irrespective of the developmental stage. Among these was extracellular arginine, which was specifically converted to ornithine by the parasite. To identify the biochemical basis for this effect, we disrupted the plasmodium arginase gene in the rodent malaria model P. berghei. These parasites were viable but did not convert arginine to ornithine. Our results suggest that systemic arginine depletion by the parasite may be a factor in human malarial hypoargininemia associated with cerebral malaria pathogenesis.

Severe atovaquone-resistant Plasmodium falciparum malaria in a Canadian traveller returned from the Indian subcontinent

BACKGROUND

We report the first case of atovaquone/proguanil treatment failure in severe Plasmodium falciparum malaria acquired by a non-immune traveller to the Indian subcontinent. Recrudescent infection was complicated by neurological involvement 14 days after directly observed therapy with atovaquone/proguanil. Sequence analysis of the plasmodial cytochrome b gene confirmed a contribution of atovaquone resistance to treatment failure. The recrudescent isolate had a single mutation at position 268 (Tyr268Cys). Video recordings illustrate dramatic but ephemeral manifestations of malaria with neurological involvement.

Inflammation and oxidative stress in vertebrate host-parasite systems

Innate, inflammation-based immunity is the first line of vertebrate defence against micro-organisms. Inflammation relies on a number of cellular and molecular effectors that can strike invading pathogens very shortly after the encounter between inflammatory cells and the intruder, but in a non-specific way. Owing to this non-specific response, inflammation can generate substantial costs for the host if the inflammatory response, and the associated oxygen-based damage, get out of control. This imposes strong selection pressure that acts to optimize two key features of the inflammatory response: the timing of activation and resolution (the process of downregulation of the response). In this paper, we review the benefits and costs of inflammation-driven immunity. Our aim is to emphasize the importance of resolution of inflammation as a way of maintaining homeostasis against oxidative stress and to prevent the 'horror autotoxicus' of chronic inflammation. Nevertheless, host immune regulation also opens the way to pathogens to subvert host defences. Therefore, quantifying inflammatory costs requires assessing (i) short-term negative effects, (ii) delayed inflammation-driven diseases, and (iii) parasitic strategies to subvert inflammation.

Lack of association of interferon regulatory factor 1 with severe malaria in affected child-parental trio studies across three African populations

Interferon Regulatory Factor 1 (IRF-1) is a member of the IRF family of transcription factors, which have key and diverse roles in the gene-regulatory networks of the immune system. IRF-1 has been described as a critical mediator of IFN-gamma signalling and as the major player in driving TH1 type responses. It is therefore likely to be crucial in both innate and adaptive responses against intracellular pathogens such as Plasmodium falciparum. Polymorphisms at the human IRF1 locus have been previously found to be associated with the ability to control P. falciparum infection in populations naturally exposed to malaria. In order to test whether genetic variation at the IRF1 locus also affects the risk of developing severe malaria, we performed a family-based test of association for 18 Single Nucleotide Polymorphisms (SNPs) across the gene in three African populations, using genotype data from 961 trios consisting of one affected child and his/her two parents (555 from The Gambia, 204 from Kenya and 202 from Malawi). No significant association with severe malaria or severe malaria subphenotypes (cerebral malaria and severe malaria anaemia) was observed for any of the SNPs/haplotypes tested in any of the study populations. Our results offer no evidence that the molecular pathways regulated by the transcription factor IRF-1 are involved in the immune-based pathogenesis of severe malaria.

Antigenic variation in Plasmodium falciparum

The persistence of the human malaria parasite Plasmodium falciparum during blood stage proliferation in its host depends on the successive expression of variant molecules at the surface of infected erythrocytes. This variation is mediated by the differential control of a family of surface molecules termed PfEMP1 encoded by approximately 60 var genes. Each individual parasite expresses a single var gene at a time, maintaining all other members of the family in a transcriptionally silent state. PfEMP1/var enables parasitized erythrocytes to adhere within the microvasculature, resulting in severe disease. This review highlights key regulatory mechanisms thought to be critical for monoallelic expression of var genes. Antigenic variation is orchestrated by epigenetic factors including monoallelic var transcription at separate spatial domains at the nuclear periphery, differential histone marks on otherwise identical var genes, and var silencing mediated by telomeric heterochromatin. In addition, controversies surrounding var genetic elements in antigenic variation are discussed.

Patterns of co-association of C-reactive protein and nitric oxide in malaria in endemic areas of Iran

In addition to numerous immune factors, C-reactive protein (CRP) and nitric oxide (NO) are believed to be molecules of malaria immunopathology. The objective of this study was to detect CRP and NO inductions by agglutination latex test and Griess microassay respectively in both control and malaria groups from endemic areas of Iran, including Southeastern (SE) (Sistan & Balouchestan, Hormozgan, Kerman) and Northwestern (NW) provinces (Ardabil). The results indicated that CRP and NO are produced in all malaria endemic areas of Iran. In addition, more CRP and NO positive cases were observed amongst malaria patients in comparison with those in control group. A variable co-association of CRP/NO production were detected between control and malaria groups, which depended upon the malaria endemic areas and the type of plasmodia infection. The percentage of CRP/NO positive cases was observed to be lower in NW compare to SE region, which may be due to the different type of plasmodium in the NW (Plasmodium vivax) with SE area (P. vivax, Plasmodium falciparum, mixed infection). The fluctuations in CRP/NO induction may be consistent with genetic background of patients. Although, CRP/NO may play important role in malaria, their actual function and interaction in clinical forms of disease remains unclear.

Obstacles to prompt and effective malaria treatment lead to low community-coverage in two rural districts of Tanzania

Background

Malaria is still a leading child killer in sub-Saharan Africa. Yet, access to prompt and effective malaria treatment, a mainstay of any malaria control strategy, is sub-optimal in many settings. Little is known about obstacles to treatment and community-effectiveness of case-management strategies. This research quantified treatment seeking behaviour and access to treatment in a highly endemic rural Tanzanian community. The aim was to provide a better understanding of obstacles to treatment access in order to develop practical and cost-effective interventions.

Methods

We conducted community-based treatment-seeking surveys including 226 recent fever episodes in 2004 and 2005. The local Demographic Surveillance System provided additional household information. A census of drug retailers and health facilities provided data on availability and location of treatment sources.

Results

After intensive health education, the biomedical concept of malaria has largely been adopted by the community. 87.5% (78.2–93.8) of the fever cases in children and 80.7% (68.1–90.0) in adults were treated with one of the recommended antimalarials (at the time SP, amodiaquine or quinine). However, only 22.5% (13.9–33.2) of the children and 10.5% (4.0–21.5) of the adults received prompt and appropriate antimalarial treatment. Health facility attendance increased the odds of receiving an antimalarial (OR = 7.7) but did not have an influence on correct dosage. The exemption system for under-fives in public health facilities was not functioning and drug expenditures for children were as high in health facilities as with private retailers.

Conclusion

A clear preference for modern medicine was reflected in the frequent use of antimalarials. Yet, quality of case-management was far from satisfactory as was the functioning of the exemption mechanism for the main risk group. Private drug retailers played a central role by complementing existing formal health services in delivering antimalarial treatment. Health system factors like these need to be tackled urgently in order to translate the high efficacy of newly introduced artemisinin-based combination therapy (ACT) into equitable community-effectiveness and health-impact.

Evolution of virulence in malaria

The pathogenesis of severe malarial disease is not yet fully understood. It is clear that host immunopathology plays a central role, and a recent paper in BMC Evolutionary Biology suggests that the ability of the parasite to stimulate interleukin-10 production is a major factor and speculates on its impact on the coevolution of host and parasite.

Febrile status, malarial parasitaemia and gastro-intestinal helminthiases in schoolchildren resident at different altitudes, in south-western Cameroon

In the many areas where human malaria and helminthiases are co-endemic, schoolchildren often harbour the heaviest infections and suffer much of the associated morbidity, especially when co-infected. In one such area, the Buea district, in south-western Cameroon, two cross-sectional surveys, together covering 263 apparently healthy schoolchildren aged 4-12 years, were recently conducted. The prevalences of fever, malarial parasitaemia and intestinal helminth infections, the seroprevalences of anti-Plasmodium falciparum IgG and IgE and anti-glycosylphosphatidylinositol (anti-GPI) IgG, plasma concentrations of total IgE, and the incidence of anaemia were all investigated. The mean (S.D.) age of the study children was 7.56 (1.82) years. Overall, 156 (59.3%) of the children were found parasitaemic, with a geometric mean parasitaemia of 565 parasites/microl. Parasitaemia and fever were significantly associated (P=0.042). The children who lived at low altitude, attending schools that lay 400-650 m above sea level, had significantly higher parasitaemias than their high-altitude counterparts (P<0.01). At low altitude, the children attending government schools had significantly higher parasitaemias than their mission-school counterparts (P=0.010). Of the 31 children (11.9%) found anaemic, 22 (70.4%) had mild anaemia and none had severe anaemia. A significant negative correlation (r=-0.224; P=0.005) was observed between haemoglobin concentration and level of parasitaemia. Infection with Plasmodium appeared to reduce erythrocyte counts (P=0.045), a condition that was exacerbated by co-infection with helminths (P=0.035). Plasma concentrations of total IgE were higher in the children found to be excreting helminth eggs than in those who appeared helminth-free, while levels of anti-P. falciparum IgE were higher in the children with low-grade parasitaemias than in those with more intense parasitaemias. Levels of anti-GPI IgG increased with age and were relatively high in the children who lived at low altitude and in those who were aparasitaemic. The survey results confirm that asymptomatic malarial parasitaemia frequently co-exists with helminth infections in schoolchildren and indicate links with fever, altitude and school type. Immunoglobulin E may play a role in immune protection against helminthiasis whereas anti-GPI antibodies may be important in the development of antimalarial immunity in such children. In Cameroon, as in other areas with endemic malaria, control programmes to reduce the prevalences of infections with intestinal helminths and malarial parasites in schoolchildren, which may effectively reduce the incidence of anaemia, are clearly needed.

Plasmodium vivax and mixed infections are associated with severe malaria in children: a prospective cohort study from Papua New Guinea

BACKGROUND

Severe malaria (SM) is classically associated with Plasmodium falciparum infection. Little information is available on the contribution of P. vivax to severe disease. There are some epidemiological indications that P. vivax or mixed infections protect against complications and deaths. A large morbidity surveillance conducted in an area where the four species coexist allowed us to estimate rates of SM among patients infected with one or several species.

METHODS AND FINDINGS

This was a prospective cohort study conducted within the framework of the Malaria Vaccine Epidemiology and Evaluation Project. All presumptive malaria cases presenting at two rural health facilities over an 8-y period were investigated with history taking, clinical examination, and laboratory assessment. Case definition of SM was based on the World Health Organization (WHO) criteria adapted for the setting (i.e., clinical diagnosis of malaria associated with asexual blood stage parasitaemia and recent history of fits, or coma, or respiratory distress, or anaemia [haemoglobin < 5 g/dl]). Out of 17,201 presumptive malaria cases, 9,537 (55%) had a confirmed Plasmodium parasitaemia. Among those, 6.2% (95% confidence interval [CI] 5.7%-6.8%) fulfilled the case definition of SM, most of them in children <5 y. In this age group, the proportion of SM was 11.7% (10.4%-13.2%) for P. falciparum, 8.8% (7.1%-10.7%) for P. vivax, and 17.3% (11.7%-24.2%) for mixed P. falciparum and P. vivax infections. P. vivax SM presented more often with respiratory distress than did P. falciparum (60% versus 41%, p = 0.002), but less often with anaemia (19% versus 41%, p = 0.0001).

CONCLUSION

P. vivax monoinfections as well as mixed Plasmodium infections are associated with SM. There is no indication that mixed infections protected against SM. Interventions targeted toward P. falciparum only might be insufficient to eliminate the overall malaria burden, and especially severe disease, in areas where P. falciparum and P. vivax coexist.

Common strategies to prevent and modulate experimental cerebral malaria in mouse strains with different susceptibilities

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection, predominantly experienced by children and nonimmune adults, which results in significant mortality and long-term sequelae. Previous studies have reported distinct susceptibility gene loci in CBA/CaH (CBA) and C57BL/6 (B6) mice with experimental CM (ECM) caused by infection with Plasmodium berghei ANKA. Here we present an analysis of genome-wide expression profiles in brain tissue taken from B6 and CBA mice with ECM and report significant heterogeneity between the two mouse strains. Upon comparison of the leukocyte composition of ECM brain tissue, microglia were expanded in B6 mice but not CBA mice. Furthermore, circulating levels of gamma interferon, interleukin-10, and interleukin-6 were significantly higher in the serum of B6 mice than in that of CBA mice with ECM. Two therapeutic strategies were applied to B6 and CBA mice, i.e., (i) depletion of regulatory T (Treg) cells prior to infection and (ii) depletion of CD8(+) T cells after the establishment of ECM. Despite the described differences between susceptible mouse strains, depletion of Treg cells before infection attenuated ECM in both B6 and CBA mice. In addition, the depletion of CD8(+) T cells when ECM symptoms are apparent leads to abrogation of ECM in B6 mice and a lack of progression of ECM in CBA mice. These results may have important implications for the development of effective treatments for human CM.

Artesunate-erythropoietin combination for murine cerebral malaria treatment

Cerebral malaria is the most severe and rapidly fatal complication of Plasmodium falciparum infection. Despite appropriate anti-malarial treatment using quinine or artemisinin derivatives, 10-20% of mortality still occurs during the acute phase. To improve cerebral malaria outcome, adjunctive therapies are clearly needed. Most experiments in this area have been dedicated to immuno-modulation with various successes. Since erythropoietin has been shown to be highly effective in human ischemic stroke and in murine cerebral malaria, we addressed the issue of cerebral malaria outcome improvement by erythropoietin-artesunate drug combination. Compared to the previous study using erythropoietin high doses at the early beginning of the disease, erythropoietin treatment was decreased by six-fold and delayed to the pre-mortem phase. We studied effects on survival and on clinical recovery of the drug combination given from day 6 to day 8 post-infection to CBA/J mice infected by Plasmodium berghei ANKA. We showed that the artesunate-erythropoietin drug combination led to clinical recovery 24 h earlier for surviving mice, and to increase in the global survival rate compared to artesunate monotherapy (p<0.01). Since erythropoietin has no effect on parasite clearance, it could be stated that this drug combination is efficient and that erythropoietin could be a lead for the implementation of a new adjunctive therapy during the acute phase of cerebral malaria.

Blood coagulation, inflammation, and malaria

Malaria remains a highly prevalent disease in more than 90 countries and accounts for at least 1 million deaths every year. Plasmodium falciparum infection is often associated with a procoagulant tonus characterized by thrombocytopenia and activation of the coagulation cascade and fibrinolytic system; however, bleeding and hemorrhage are uncommon events, suggesting that a compensated state of blood coagulation activation occurs in malaria. This article (i) reviews the literature related to blood coagulation and malaria in a historic perspective, (ii) describes basic mechanisms of coagulation, anticoagulation, and fibrinolysis, (iii) explains the laboratory changes in acute and compensated disseminated intravascular coagulation (DIC), (iv) discusses the implications of tissue factor (TF) expression in the endothelium of P. falciparum infected patients, and (v) emphasizes the procoagulant role of parasitized red blood cells (RBCs) and activated platelets in the pathogenesis of malaria. This article also presents the Tissue Factor Model (TFM) for malaria pathogenesis, which places TF as the interface between sequestration, endothelial cell (EC) activation, blood coagulation disorder, and inflammation often associated with the disease. The relevance of the coagulation-inflammation cycle for the multiorgan dysfunction and coma is discussed in the context of malaria pathogenesis.

Increased microerythrocyte count in homozygous alpha(+)-thalassaemia contributes to protection against severe malarial anaemia

BACKGROUND

The heritable haemoglobinopathy alpha(+)-thalassaemia is caused by the reduced synthesis of alpha-globin chains that form part of normal adult haemoglobin (Hb). Individuals homozygous for alpha(+)-thalassaemia have microcytosis and an increased erythrocyte count. Alpha(+)-thalassaemia homozygosity confers considerable protection against severe malaria, including severe malarial anaemia (SMA) (Hb concentration < 50 g/l), but does not influence parasite count. We tested the hypothesis that the erythrocyte indices associated with alpha(+)-thalassaemia homozygosity provide a haematological benefit during acute malaria.

METHODS AND FINDINGS

Data from children living on the north coast of Papua New Guinea who had participated in a case-control study of the protection afforded by alpha(+)-thalassaemia against severe malaria were reanalysed to assess the genotype-specific reduction in erythrocyte count and Hb levels associated with acute malarial disease. We observed a reduction in median erythrocyte count of approximately 1.5 x 10(12)/l in all children with acute falciparum malaria relative to values in community children (p < 0.001). We developed a simple mathematical model of the linear relationship between Hb concentration and erythrocyte count. This model predicted that children homozygous for alpha(+)-thalassaemia lose less Hb than children of normal genotype for a reduction in erythrocyte count of >1.1 x 10(12)/l as a result of the reduced mean cell Hb in homozygous alpha(+)-thalassaemia. In addition, children homozygous for alpha(+)-thalassaemia require a 10% greater reduction in erythrocyte count than children of normal genotype (p = 0.02) for Hb concentration to fall to 50 g/l, the cutoff for SMA. We estimated that the haematological profile in children homozygous for alpha(+)-thalassaemia reduces the risk of SMA during acute malaria compared to children of normal genotype (relative risk 0.52; 95% confidence interval [CI] 0.24-1.12, p = 0.09).

CONCLUSIONS

The increased erythrocyte count and microcytosis in children homozygous for alpha(+)-thalassaemia may contribute substantially to their protection against SMA. A lower concentration of Hb per erythrocyte and a larger population of erythrocytes may be a biologically advantageous strategy against the significant reduction in erythrocyte count that occurs during acute infection with the malaria parasite Plasmodium falciparum. This haematological profile may reduce the risk of anaemia by other Plasmodium species, as well as other causes of anaemia. Other host polymorphisms that induce an increased erythrocyte count and microcytosis may confer a similar advantage.

Apoptosis: a potential triggering mechanism of neurological manifestation in Plasmodium falciparum malaria

Plasmodium falciparum infection can lead to a life threatening disease and the pathogenetic mechanisms of severe manifestations are not fully understood. Here, we investigated the capacity of P. falciparum-parasitized red blood cells (PRBC) from 45 children with clinical malaria to induce endothelial cell (EC) apoptosis. In all subjects, PRBC that cytoadhered to ECs could be found albeit to a variable degree. By contrast, PRBC that induce EC apoptosis were found only in nine (20%) subjects. Interestingly, children with neurological manifestations were significantly more likely to harbour apoptogenic strains. There was no quantitative relationship between the capacity of these isolates to cytoadhere and apoptosis induction. We hypothesize that P. falciparum-encoded molecules could be responsible for apoptosis induction and therefore suggest new insights in the pathogenesis of P. falciparum malaria. Further investigations are currently in progress to determine whether these results can be confirmed and to identify putative parasite apoptogenic factors.

Plasmodium infection and endotoxic shock induce the expansion of regulatory dendritic cells

During an acute Plasmodium infection, uncontrolled proinflammatory responses can cause morbidity and mortality. Regulation of this response is required to prevent immunopathology. We therefore decided to investigate a recently characterized subset of regulatory dendritic cells (DCs) that expresses low levels of CD11c and high levels of CD45RB. During a Plasmodium yoelii infection, these regulatory CD11clowCD45RBhigh DCs become the prevalent CD11c-expressing cells in the spleen, overtaking the conventional CD11chigh DCs. Furthermore, the regulatory CD11clowCD45RBhigh DCs induce IL-10-expressing CD4 T cells. A similar change in splenic DC subsets is seen when mice are injected with sublethal doses of LPS, suggesting that shifting the splenic DC subsets in favor of regulatory CD11clowCD45RBhigh DCs can be triggered solely by a high inflammatory stimulus. This is the first time regulatory DCs have been observed in a natural immune response to an infectious disease or endotoxic shock.

Plasmodium-induced inflammation by uric acid

Infection of erythrocytes with the Plasmodium parasite causes the pathologies associated with malaria, which result in at least one million deaths annually. The rupture of infected erythrocytes triggers an inflammatory response, which is induced by parasite-derived factors that still are not fully characterized. Induced secretion of inflammatory cytokines by these factors is considered a major cause of malaria pathogenesis. In particular, the inflammatory cytokine tumor necrosis factor (TNF) is thought to mediate most of the life-threatening pathologies of the disease. Here we describe the molecular characterization of a novel pathway that results in the secretion of TNF by host cells. We found that erythrocytes infected by Plasmodium accumulate high concentrations of hypoxanthine and xanthine. Degradation of Plasmodium-derived hypoxanthine/xanthine results in the formation of uric acid, which triggers the secretion of TNF. Since uric acid is considered a "danger signal" released by dying cells to alert the immune system, Plasmodium appears to have co-evolved to exploit this warning system. Identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease.

Malaria in rural Mozambique. Part II: children admitted to hospital

Background

Characterization of severe malaria cases on arrival to hospital may lead to early recognition and improved management. Minimum community based-incidence rates (MCBIRs) complement hospital data, describing the malaria burden in the community.

Methods

A retrospective analysis of all admitted malaria cases to a Mozambican rural hospital between June 2003 and May 2005 was conducted. Prevalence and case fatality rates (CFR) for each sign and symptom were calculated. Logistic regression was used to identify variables which were independent risk factors for death. MCBIRs for malaria and severe malaria were calculated using data from the Demographic Surveillance System.

Results

Almost half of the 8,311 patients admitted during the study period had malaria and 13,2% had severe malaria. Children under two years accounted for almost 60% of all malaria cases. CFR for malaria was 1.6% and for severe malaria 4.4%. Almost 19% of all paediatric hospital deaths were due to malaria. Prostration (55.0%), respiratory distress (41.1%) and severe anaemia (17.3%) were the most prevalent signs among severe malaria cases. Severe anaemia and inability to look for mother's breast were independent risk factors for death in infants younger than eight months. For children aged eight months to four years, the risk factors were malnutrition, hypoglycaemia, chest indrawing, inability to sit and a history of vomiting.

MCBIRs for severe malaria cases were highest in children aged six months to two years of age. MCBIRs for severe malaria per 1,000 child years at risk for the whole study period were 27 in infants, 23 in children aged 1 to <5 years and two in children aged ≥5 years.

Conclusion

Malaria remains the number one cause of admission in this area of rural Mozambique, predominantly affecting young children, which are also at higher risk of dying. Measures envisaged to protect children during their first two years of life are likely to have a greater impact than at any other age.

Plasmepsins as potential targets for new antimalarial therapy

Malaria is one of the major diseases in the world. Due to the rapid spread of parasite resistance to available antimalarial drugs there is an urgent need for new antimalarials with novel mechanisms of action. Several promising targets for drug intervention have been revealed in recent years. This review addresses the parasitic aspartic proteases termed plasmepsins (Plms) that are involved in the hemoglobin catabolism that occurs during the erythrocytic stage of the malarial parasite life cycle. Four Plasmodium species are responsible for human malaria; P. vivax, P. ovale, P. malariae, and P. falciparum. This review focuses on inhibitors of the haemoglobin-degrading plasmepsins of the most lethal species, P. falciparum; Plm I, Plm II, Plm IV, and histo-aspartic protease (HAP). Previously, Plm II has attracted the most attention. With the identification and characterization of new plasmepsins and the results from recent plasmepsin knockout studies, it now seems clear that in order to achieve high-antiparasitic activities in P. falciparum-infected erythrocytes it is necessary to inhibit several of the haemoglobin-degrading plasmepsins. Herein we summarize the structure-activity relationships of the Plm I, II, IV, and HAP inhibitors. These inhibitors represent all classes which, to the best of our knowledge, have been disclosed in journal articles to date. The 3D structures of inhibitor/plasmepsin II complexes available in the protein data bank are briefly discussed and compared.

Coadaptation and malaria control

Malaria emerges from a disequilibrium of the system 'human-plasmodium-mosquito' (HPM). If the equilibrium is maintained, malaria does not ensue and the result is asymptomatic plasmodium infection. The relationships among the components of the system involve coadaptive linkages that lead to equilibrium. A vast body of evidence supports this assumption, including the strategies involved in the relationships between plasmodium and human and mosquito immune systems, and the emergence of resistance of plasmodia to antimalarial drugs and of mosquitoes to insecticides. Coadaptive strategies for malaria control are based on the following principles: (1) the system HPM is composed of three highly complex and dynamic components, whose interplay involves coadaptive linkages that tend to maintain the equilibrium of the system; (2) human and mosquito immune systems play a central role in the coadaptive interplay with plasmodium, and hence, in the maintenance of the system's equilibrium; the under- or overfunction of human immune system may result in malaria and influence its severity; (3) coadaptation depends on genetic and epigenetic phenomena occurring at the interfaces of the components of the system, and may involve exchange of infectrons (genes or gene fragments) between the partners; (4) plasmodia and mosquitoes have been submitted to selective pressures, leading to adaptation, for an extremely long while and are, therefore, endowed with the capacity to circumvent both natural (immunity) and artificial (drugs, insecticides, vaccines) measures aiming at destroying them; (5) since malaria represents disequilibrium of the system HPM, its control should aim at maintaining or restoring this equilibrium; (6) the disequilibrium of integrated systems involves the disequilibrium of their components, therefore the maintenance or restoration of the system's equilibrium depend on the adoption of integrated and coordinated measures acting on all components, that means, panadaptive strategies. Coadaptive strategies for malaria control should consider that: (1) host immune response has to be induced, since without it, no coadaptation is attained; (2) the immune response has to be sustained and efficient enough to avoid plasmodium overgrowth; (3) the immune response should not destroy all parasites; (4) the immune response has to be well controlled in order to not harm the host. These conditions are mostly influenced by antimalarial drugs, and should also be taken into account for the development of coadaptive malaria vaccines.

Clinical manifestations and predictors of severe malaria in Indian children

OBJECTIVE

Although the greatest morbidity and mortality attributable to malaria occurs among children in Africa, up to one third of the world's malaria burden is borne by non-African countries, where levels of endemicity are lower. Because there are few published criteria for managing life-threatening malaria in children in these countries, we conducted a study of major syndromes and predictors of death among critically ill Indian children to identify factors that could be used to improve the approach to their treatment.

METHODS

A prospective study was conducted at the pediatric ward of SCB Medical College in eastern India (Orissa). Baseline demographic data were collected on all of the patients with confirmed slide-positive falciparum malaria. Patients satisfying any 1 of the 2000 World Health Organization criteria for severe malaria were included in the analysis. Prevalence of and mortality as a result of major symptoms were calculated followed by multiple regression modeling to identify major predictors of death.

RESULTS

Of 1682 confirmed cases of malaria during a 32-month period, 374 subjects met the World Health Organization criteria for severe malaria. The case fatality rate was 12% in this series. Multiple regression analysis identified respiratory distress, coma, multiple organ dysfunctions, and hyperparasitemia as major predictors of death. Anemia and jaundice did not emerge as important markers of mortality. Many patients presented with multiple major complications, and the mortality rate was consistently high when >1 major predictor was present in a patient.

CONCLUSIONS

Clinical features in Indian children differed from those reported in most studies that involved an African population. Multiple organ dysfunctions emerged as an important presenting feature and a new predictor of death in childhood malaria.

Vaccines against malaria - an update

Malaria vaccine discovery and development follow two principal strategies. Most subunit vaccines are designed to mimic naturally acquired immunity that develops over years upon continuous exposure to Plasmodium transmission. Experimental model vaccines, such as attenuated live parasites and transmission-blocking antigens, induce immune responses superior to naturally acquired immunity. The promises and hurdles of the different tracks towards an effective and affordable vaccine against malaria are discussed.

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

A low-sulfated chondroitin sulfate proteoglycan (CSPG) has been shown to be the receptor for the adherence of Plasmodium falciparum-infected red blood cells (IRBCs) in human placenta. Recently, hyaluronic acid (HA) has been suggested as an additional receptor even though IRBC binding to HA and the presence of HA at locations where IRBCs adhere in the placenta have not been established. In this study, we investigated whether HA is also a receptor for IRBC binding. IRBCs from infected placentas as well as those from different laboratory strains could bind to CSPG but not to HA. In a cell depletion assay, IRBCs from infected placentas could bind quantitatively to CSPG. Although CSPG is present both in the intervillous space and on the syncytiotrophoblast surface, HA is absent in these locations. These data conclusively demonstrate that CSPG, but not HA, is a receptor for IRBC adherence in the placenta. Our data also show, for the first time, that the IRBC-binding CSPG in the placenta is of fetal origin and that, in P. falciparum-infected placentas, the CSPG level is significantly increased, which could exacerbate IRBC adherence and placental pathogenesis. These results have important implications for the development of anti-IRBC adhesion-based vaccine for pregnancy-associated malaria.

A role for natural regulatory T cells in the pathogenesis of experimental cerebral malaria

Cerebral malaria (CM) is a serious complication of Plasmodium falciparum infection that is responsible for a significant number of deaths in children and nonimmune adults. A failure to control blood parasitemia and subsequent sequestration of parasites to brain microvasculature are thought to be key events in many CM cases. Here, we show for the first time, to our knowledge, that CD4(+)CD25(+)Foxp3(+) natural regulatory T (Treg) cells contribute to pathogenesis by modulating immune responses in P. berghei ANKA (PbA)-infected mice. Depletion of Treg cells with anti-CD25 monoclonal antibody protected mice from experimental CM. The accumulation of parasites in the vasculature and brain was reduced in these animals, resulting in significantly lower parasite burdens compared with control animals. Mice lacking Treg cells had increased numbers of activated CD4(+) and CD8(+) T cells in the spleen and lymph nodes, but CD8(+) T-cell recruitment to the brain was selectively reduced in these mice. Importantly, a non-Treg-cell source of interleukin-10 was critical in preventing experimental CM. Finally, we show that therapeutic administration of anti-CD25 monoclonal antibody, even when blood parasitemia is established, can prevent disease, confirming a critical and paradoxical role for Treg cells in experimental CM pathogenesis.

Real-time in vivo imaging of transgenic bioluminescent blood stages of rodent malaria parasites in mice

This protocol describes a methodology for imaging the sequestration of infected erythrocytes of the rodent malaria parasite Plasmodium berghei in the bodies of live mice or in dissected organs, using a transgenic parasite that expresses luciferase. Real-time imaging of infected erythrocytes is performed by measuring bioluminescence produced by the enzymatic reaction between luciferase and its substrate luciferin, which is injected into the mice several minutes prior to imaging. The bioluminescence signal is detected by an intensified charge-coupled device (I-CCD) photon-counting video camera. Sequestration of infected erythrocytes is imaged during short-term infections with synchronous parasite development or during ongoing infections. With this technology, sequestration patterns of the schizont stage can be quantitatively analyzed within 1-2 d after infection. Real-time in vivo imaging of infected erythrocytes will provide increased insights into the dynamics of sequestration and its role in pathology, and can be used to evaluate strategies that prevent sequestration.

Age-related changes in adaptation to severe anemia in childhood in developing countries

Severe forms of anemia in children in the developing countries may be characterized by different clinical manifestations at particular stages of development. Whether this reflects developmental changes in adaptation to anemia or other mechanisms is not clear. The pattern of adaptation to anemia has been assessed in 110 individuals with hemoglobin (Hb) E beta-thalassemia, one of the commonest forms of inherited anemia in Asia. It has been found that age and Hb levels are independent variables with respect to erythropoietin response and that there is a decline in the latter at a similar degree of anemia during development. To determine whether this finding is applicable to anemia due to other causes, a similar study has been carried out on 279 children with severe anemia due to Plasmodium falciparum malaria; the results were similar to those in the patients with thalassemia. These observations may have important implications both for the better understanding of the pathophysiology of profound anemia in early life and for its more logical and cost-effective management.

Germinal center architecture disturbance during Plasmodium berghei ANKA infection in CBA mice

Background

Immune responses to malaria blood stage infection are in general defective, with the need for long-term exposure to the parasite to achieve immunity, and with the development of immunopathology states such as cerebral malaria in many cases. One of the potential reasons for the difficulty in developing protective immunity is the poor development of memory responses. In this paper, the potential association of cellular reactivity in lymphoid organs (spleen, lymph nodes and Peyer's patches) with immunity and pathology was evaluated during Plasmodium berghei ANKA infection in CBA mice.

Methods

CBA mice were infected with 1 × 10⁶ P. berghei ANKA-parasitized erythrocytes and killed on days 3, 6–8 and 10 of infection. The spleen, lymph nodes and Peyer's patches were collected, fixed in Carson's formalin, cut in 5 μm sections, mounted in glass slides, stained with Lennert's Giemsa and haematoxylin-eosin and analysed with bright-field microscopy.

Results

Early (day 3) strong activation of T cells in secondary lymphoid organs was observed and, on days 6–8 of infection, there was overwhelming activation of B cells, with loss of conventional germinal center architecture, intense centroblast activation, proliferation and apoptosis but little differentiation to centrocytes. In the spleen, the marginal zone disappeared and the limits between the disorganized germinal center and the red pulp were blurred. Intense plasmacytogenesis was observed in the T cell zone.

Conclusion

The observed alterations, especially the germinal center architecture disturbance (GCAD) with poor centrocyte differentiation, suggest that B cell responses during P. berghei ANKA infection in mice are defective, with potential impact on B cell memory responses.

Axonal and astrocyte injury markers in the cerebrospinal fluid of Kenyan children with severe malaria

A retrospective study of cerebrospinal fluid (CSF) levels of markers of brain parenchymal damage was conducted in Kenyan children with severe falciparum malaria. Two markers were analysed by immunoassays: the microtubule-associated protein tau for degenerated axons and S-100B for astrocytes. The level of tau proteins in the CSF was significantly elevated in children with cerebral malaria compared with either malaria with prostration or malaria with seizures but normal consciousness (p<0.001). Elevated tau was also found to be associated with impaired delivery of oxygen (severe anaemia), severe metabolic acidosis manifesting as respiratory distress (increased respiratory rate and deep acidotic breathing) and at higher parasite densities. Elevated S-100B in children was associated with an increased risk of repeated seizures. This study provides evidence that axonal injury is associated with malaria coma and identifies the potential role of severe anaemia, acidosis and hyperparasitaemia to causing brain parenchymal damage in children with malaria.

Severe malaria in Cameroonian children: correlation between plasma levels of three soluble inducible adhesion molecules and TNF-alpha

Plasma levels of three soluble inducible adhesion molecules, namely: intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1) and endothelial leucocyte adhesion molecule-1 (sELAM-1) or sE-selectin and the pro-inflammatory cytokine, tumour necrosis factor-alpha (TNF-alpha) were measured in well-defined clinical groups of children with severe and uncomplicated malaria. The goal of the study was to investigate the role of these molecules in immunopathogenic processes associated with severe malaria in Cameroonian children. Results showed significantly increased plasma concentrations of sICAM-1, sVCAM-1 and sE-selectin in children with severe malaria compared to those with uncomplicated malaria and healthy children (P<0.001). TNF-alpha levels increased significantly in children with severe malaria, approximately 2-folds compared to those with uncomplicated malaria and about 3-folds compared to healthy children (P<0.001). More importantly, levels of TNF-alpha strongly correlated with those of the three adhesion molecules and were significantly associated with increased risk of death (P=0.03). In addition, children who died from severe malaria showed higher mean levels of all measured factors compared to those who recovered, with significant differences observed with sICAM-1 (P<0.001) and sE-selectin (P=0.002). Furthermore, children with severe malarial anemia relative to those without, showed significantly elevated levels of the three soluble molecules; and sICAM-1 was significantly associated with increased risk of severe anemia. Taken together, these results confirm the role of TNF-alpha and the three adhesion molecules in pathogenic processes associated with severe malaria in children, and suggest an association between sICAM-1 and severe malarial anemia.

Plasmodium berghei ANKA infection induces thymocyte apoptosis and thymocyte depletion in CBA mice

Immune responses to malaria infections are characterized by strong T and B cell activation, which, in addition of potentially causing immunopathology, are of poor efficacy against the infection. It is possible that the thymus is involved in the origin of immunopathological reactions and a target during malaria infections. This work was developed in an attempt to further clarify these points. We studied the sequential changes in the thymus of CBA mice infected with Plasmodium berghei ANKA, a model in which 60-90% of the infected animals develop cerebral malaria. During the acute phase of infection, different degrees of thymocyte apoptosis were recorded. (1) starry-sky pattern of diffuse apoptosis with maintenance of cortical-medullary structure; (2) intense apoptosis with cortical atrophy, with absence of large cells; (3) severe cortical thymocyte depletion, resulting in cortical-medullary inversion. In the latter, only residual clusters of small thymocytes were observed within the framework of epithelial cells. The intensity of thymus alterations could not be associated with the degree of parasitemia, the expression of clinical signs of cerebral malaria or intensity of brain lesions. The implications of these events for malaria immunity and pathology are discussed.

Magnetic resonance spectroscopy reveals an impaired brain metabolic profile in mice resistant to cerebral malaria infected with Plasmodium berghei ANKA

Malaria is a major cause of morbidity and mortality with an annual death toll exceeding one million. Severe malaria is a complex multisystem disorder, including one or more of the following complications: cerebral malaria, anemia, acidosis, jaundice, respiratory distress, renal insufficiency, coagulation anomalies, and hyperparasitemia. Using a combined in vivo/in vitro metabolic-based approach, we investigated the putative pathogenic effects of Plasmodium berghei ANKA on brain, in a mouse strain developing malaria but resistant to cerebral malaria. The purpose was to determine whether the infection could cause a brain dysfunction distinct from the classic cerebral syndrome. Mice resistant to cerebral malaria were infected with P. berghei ANKA and explored during both the symptomless and the severe stage of the disease by using in vivo brain magnetic resonance imaging and spectroscopy. The infected mice did not present the lesional and metabolic hallmarks of cerebral malaria. However, brain dysfunction caused by anemia, parasite burden, and hepatic damage was evidenced. We report an increase in cerebral blood flow, a process allowing temporary maintenance of oxygen supply to brain despite anemia. Besides, we document metabolic anomalies affecting choline-derived compounds, myo-inositol, glutamine, glycine, and alanine. The choline decrease appears related to parasite proliferation. Glutamine, myo-inositol, glycine, and alanine variations together indicate a hepatic encephalopathy, a finding in agreement with the liver damage detected in mice, which is also a feature of the human disease. These results reveal the vulnerability of brain to malaria infection at the severe stage of the disease even in the absence of cerebral malaria.

Transcriptome profile of dendritic cells during malaria: cAMP regulation of IL-6

Dendritic cells (DCs) have been proposed as mediators of immunity against malaria parasites, as well as a target for inhibition of cellular responses. Here we describe the transcriptomic analysis of spleen DCs in response to Plasmodium infection in a rodent model. We identified a high number of unique transcripts modulated in DCs upon infection. Many cellular functions suffer extensive genomic regulation including the cell cycle, the glycolysis and purine metabolism pathways and also defence responses. Only a small fraction of the regulated genes are coincident with the response induced by other pathogens, suggesting that Plasmodium induces a unique genetic re-programming of DCs. We confirmed regulation of a number of cytokines at the mRNA level including IL-6, IL-10 and IFN-gamma. We further dissected a signalling pathway regulating Plasmodium-induced expression of IL-6 by DCs, which is mediated by release of PGE2, increases in intracellular cAMP and activation of PKA and p38-MAPK.

Falciparum Malaria

Malaria is one of the most common infectious diseases in the world today, being the most important parasitic infection, and Plasmodium falciparum is the organism responsible for most of the mortality [1]. It has been estimated that approximately 300–500 million people contract malaria every year, with approximately 1–2 million deaths, most of these occurring in children [1–5]. Plasmodium falciparum, Mycobacterium tuberculosis and measles currently compete for the title of the single most important pathogen causing human morbidity and mortality [2, 3]. Infection with Plasmodium falciparum has a wide variety of potential clinical consequences [4, 6, 7].

Disruption of JNK2 decreases the cytokine response to Plasmodium falciparum glycosylphosphatidylinositol in vitro and confers protection in a cerebral malaria model

Host inflammatory responses to Plasmodium falciparum GPI (pfGPI) anchors are believed to play an important role in the pathophysiology of severe malaria. However, relatively little is known about the signal transduction pathways involved in pfGPI-stimulated inflammatory response and its potential contribution to severe malaria syndromes. In this study, we investigated the role of MAPK activation in pfGPI-induced cytokine secretion and examined the role of selected MAPKs in a model of cerebral malaria in vivo. We demonstrate that ERK1/2, JNK, p38, c-Jun, and activating transcription factor-2 became phosphorylated in pfGPI-stimulated macrophages. A JNK inhibitor (1,9-pyrazoloanthrone) inhibited pfGPI-induced phosphorylation of JNK, c-Jun, and activating transcription factor-2 and significantly decreased pfGPI-induced TNF-alpha secretion. pfGPI-stimulated JNK and c-Jun phosphorylation was absent in Jnk2(-/-) macrophages but unchanged in Jnk1(-/-) and Jnk3(-/-) macrophages compared with wild-type macrophages. Jnk2(-/-) macrophages secreted significantly less TNF-alpha in response to pfGPI than macrophages from Jnk1(-/-), Jnk3(-/-), and wild-type counterparts. Furthermore, we demonstrate a role for JNK2 in mediating inflammatory responses and severe malaria in vivo. In contrast to wild-type or Jnk1(-/-) mice, Jnk2(-/-) mice had lower levels of TNF-alpha in vivo and exhibited significantly higher survival rates when challenged with Plasmodium berghei ANKA. These results provide direct evidence that pfGPI induces TNF-alpha secretion through activation of MAPK pathways, including JNK2. These results suggest that JNK2 is a potential target for therapeutic interventions in severe malaria.

Common and divergent immune response signaling pathways discovered in peripheral blood mononuclear cell gene expression patterns in presymptomatic and clinically apparent malaria

Using genome-wide expression profiles from persons either experimentally challenged with malaria-infected mosquitoes or naturally infected with Plasmodium falciparum malaria, we present details of the transcriptional changes that occur with infection and that either are commonly shared between subjects with presymptomatic and clinically apparent malaria or distinguish these two groups. Toll-like receptor signaling through NF-kappaB pathways was significantly upregulated in both groups, as were downstream genes that function in phagocytosis and inflammation, including the cytokines tumor necrosis factor alpha, gamma interferon (IFN-gamma), and interleukin-1beta (IL-1beta). The molecular program derived from these signatures illuminates the closely orchestrated interactions that regulate gene expression by transcription factors such as IRF-1 in the IFN-gamma signal transduction pathway. Modulation of transcripts in heat shock and glycolytic enzyme genes paralleled the intensity of infection. Major histocompatibility complex class I molecules and genes involved in class II antigen presentation are significantly induced in 90% of malaria-infected persons regardless of group. Differences between early presymptomatic infection and natural infection involved genes that regulate the induction of apoptosis through mitogen-activated protein (MAP) kinases and signaling pathways through the endogenous pyrogen IL-1beta, a major inducer of fever. The induction of apoptosis in peripheral blood mononuclear cells from patients with naturally acquired infection impacted the mitochondrial control of apoptosis and the activation of MAP kinase pathways centered around MAPK14 (p38alpha and p38beta). Our findings confirm and extend findings regarding aspects of the earliest responses to malaria infection at the molecular level, which may be informative in elucidating how innate and adaptive immune responses may be modulated in different stages of infection.

Simultaneous host and parasite expression profiling identifies tissue-specific transcriptional programs associated with susceptibility or resistance to experimental cerebral malaria

Background

The development and outcome of cerebral malaria (CM) reflects a complex interplay between parasite-expressed virulence factors and host response to infection. The murine CM model, Plasmodium berghei ANKA (PbA), which simulates many of the features of human CM, provides an excellent system to study this host/parasite interface. We designed "combination" microarrays that concurrently detect genome-wide transcripts of both PbA and mouse, and examined parasite and host transcriptional programs during infection of CM-susceptible (C57BL/6) and CM-resistant (BALB/c) mice.

Results

Analysis of expression data from brain, lung, liver, and spleen of PbA infected mice showed that both host and parasite gene expression can be examined using a single microarray, and parasite transcripts can be detected within whole organs at a time when peripheral blood parasitemia is low. Parasites display a unique transcriptional signature in each tissue, and lung appears to be a large reservoir for metabolically active parasites. In comparisons of susceptible versus resistant animals, both host and parasite display distinct, organ-specific transcriptional profiles. Differentially expressed mouse genes were related to humoral immune response, complement activation, or cell-cell interactions. PbA displayed differential expression of genes related to biosynthetic activities.

Conclusion

These data show that host and parasite gene expression profiles can be simultaneously analysed using a single "combination" microarray, and that both the mouse and malaria parasite display distinct tissue- and strain-specific responses during infection. This technology facilitates the dissection of host-pathogen interactions in experimental cerebral malaria and could be extended to other disease models.