Indiana University-Purdue University Indianapolis (IUPUI) / Severe malaria, primarily caused by Plasmodium falciparum infection, is among the leading causes of childhood mortality globally. A key virulence factor and source of antigenic variation and immune evasion during infection is P. falciparum erythrocyte membrane protein 1 (PfEMP1). Encoded for by approximately 60 var genes, this complex protein mediates cytoadherence of infected erythrocytes to the host endothelium and is a prominent immune target for the anti-malarial immune response in children. During severe malaria, specific domains of PfEMP1 that bind to endothelial protein C receptor (EPCR) and intercellular adhesion molecule-1 (ICAM-1) on host endothelial cells, are more prevalently expressed. The interaction of these proteins and infected erythrocytes mediates the sequestration of infected erythrocytes and plays a role in severe malaria pathogenesis. Antibodies to these domains develop over time with exposure to the parasite and are thought to contribute to immunity against severe malaria in children. In this study, whole blood samples from children with different forms of severe malaria, enrolled in two observational prospective cohort studies were used to quantify the expression of PfEMP1 domains using RT-qPCR and to measure the antibody response to PfEMP1 domains via a bead-based multiplex immunoassay. Using these samples, we demonstrated that although the expression of var transcripts encoding PfEMP1 domains was generally similar across children with different forms of severe malaria, the expression of variants encoding specific EPCR-binding domains was associated with thrombocytopenia and severe anemia. The antibody response to PfEMP1 domains in children with severe malaria was highest in children with SMA and children with asymptomatic parasitemia, but not associated with decreased risk of additional malaria episodes. Overall, the results of this study suggest that PfEMP1 is acting similarly across different forms of severe malaria but that it can be related to pathogenesis and severe malaria immunity.

Indiana University-Purdue University Indianapolis (IUPUI) / Artemisinin resistance was first observed in Southeast Asia (SEA) and could pose a threat to malaria treatment all over the world. Recently mutations in the propeller region of Pfkelch13 gene have been used as a genetic marker for resistance observed in SEA. We investigated the presence of mutations in the Pfkelch gene in children in Kampala, Uganda with severe malaria (SM) treated with intravenous quinine, or with asymptomatic P.falciparum infection (AP) treated with artemether-lumefantrine. We sequenced the Pfkelch gene (2178bp) in 157 children with SM and 49 children with AP infection. In children with SM and AP we identified 106 (60.8%) and 27 (55.1%) parasites with mutations upstream of the Pfkelch13 propeller region. The two most prevalent mutations were 142NN (26.1% in SM, 33% in AP) and K189T (16.5% in SM, 12.2% in AP). In SM, only a single infection had a mutation in the propeller region (A578S), while in AP, mutations in the propeller region included A578S (n=1) and S522C (n=1). In children with SM, parasites with 142NN insertion compared to 3D7 Pfkelch13 parasites had lower parasite density (p=0.02) and lower parasite biomass (p=0.03). Children with SM who either had 142NN or K189T mutation cleared parasites after quinine treatment faster than those with the 3D7 Pfkelch13 genotype (P<0.001 for both mutations compared to 3D7). In this cohort mutations, upstream of the Pfkelch13 propeller region were common. Future studies will assess the presence of Pfcrt and Pfmdr mutations in this cohort, and how these relate to the Pfkelch13 mutations and to parasite clearance.

Severe manifestations of malaria, including cerebral malaria (CM) and respiratory distress, result in approximately three million deaths annually worldwide. Currently, relatively little is known about severe disease pathogenesis. The development and outcome of severe malaria is determined by host-pathogen interactions, a complex interface of genetics and immune responses. Hypothetically, a spectrum of genetic susceptibility and resistance to severe disease exists within the host population, and malaria infection results in diverse host and parasite responses that impact disease outcome. The aim of this study was to identify differential host and parasite responses in a murine model of severe malaria, Plasmodium berghei ANKA (PbA), in CM-susceptible and CM-resistant mice; and to analyze host genetics in patients with severe disease due to Plasmodium falciparum. In vivo, expression microarray analysis showed that, in malaria target organs, differential responses were related to immune response – primarily interferon and complement pathways – and apoptosis. Histopathological examination of the brain confirmed an increased prevalence of apoptosis in CM-susceptible mice. Further examination of the role of complement in CM-susceptibility determined that early complement 5 (C5) activation conferred susceptibility to CM, and that C5 deficiency conferred resistance, which could be recapitulated by antibody blockade of activated C5 or its receptor in susceptible mice. Additionally, single nucleotide polymorphism (SNP) studies identified that complement receptor 1 SNPs were associated with disease severity in patients with P. falciparum malaria. PbA parasites displayed a unique transcriptional signature in each tissue examined (brain, liver, spleen and lung), showed differential gene expression between CM-resistant and susceptible hosts, and were most prominent in lung tissue. Closer examination of lung involvement in PbA infection revealed that PbA-infected C57BL/6 mice develop acute lung injury (ALI), defined by disruption of the alveolar-capillary membrane barrier. ALI susceptibility did not correlate with CM susceptibility, but was influenced by peripheral parasite burden and CD36-mediated parasite sequestration in the lung. PbA provides a clinically relevant experimental model for CM and ALI, through which important disease mechanisms can be identified and modulated. Ideally, the use of such models aids in the discovery of disease biomarkers and novel therapeutic strategies, which may be applied to human severe and cerebral malaria.

Severe manifestations of malaria, including cerebral malaria (CM) and respiratory distress, result in approximately three million deaths annually worldwide. Currently, relatively little is known about severe disease pathogenesis. The development and outcome of severe malaria is determined by host-pathogen interactions, a complex interface of genetics and immune responses. Hypothetically, a spectrum of genetic susceptibility and resistance to severe disease exists within the host population, and malaria infection results in diverse host and parasite responses that impact disease outcome. The aim of this study was to identify differential host and parasite responses in a murine model of severe malaria, Plasmodium berghei ANKA (PbA), in CM-susceptible and CM-resistant mice; and to analyze host genetics in patients with severe disease due to Plasmodium falciparum. In vivo, expression microarray analysis showed that, in malaria target organs, differential responses were related to immune response – primarily interferon and complement pathways – and apoptosis. Histopathological examination of the brain confirmed an increased prevalence of apoptosis in CM-susceptible mice. Further examination of the role of complement in CM-susceptibility determined that early complement 5 (C5) activation conferred susceptibility to CM, and that C5 deficiency conferred resistance, which could be recapitulated by antibody blockade of activated C5 or its receptor in susceptible mice. Additionally, single nucleotide polymorphism (SNP) studies identified that complement receptor 1 SNPs were associated with disease severity in patients with P. falciparum malaria. PbA parasites displayed a unique transcriptional signature in each tissue examined (brain, liver, spleen and lung), showed differential gene expression between CM-resistant and susceptible hosts, and were most prominent in lung tissue. Closer examination of lung involvement in PbA infection revealed that PbA-infected C57BL/6 mice develop acute lung injury (ALI), defined by disruption of the alveolar-capillary membrane barrier. ALI susceptibility did not correlate with CM susceptibility, but was influenced by peripheral parasite burden and CD36-mediated parasite sequestration in the lung. PbA provides a clinically relevant experimental model for CM and ALI, through which important disease mechanisms can be identified and modulated. Ideally, the use of such models aids in the discovery of disease biomarkers and novel therapeutic strategies, which may be applied to human severe and cerebral malaria.

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-06-19T16:07:50Z No. of bitstreams: 1 saramalagutiandradesoares.pdf: 1936313 bytes, checksum: bac06dfaa717be34b6dd2753dd6bf232 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-06-29T12:30:09Z (GMT) No. of bitstreams: 1 saramalagutiandradesoares.pdf: 1936313 bytes, checksum: bac06dfaa717be34b6dd2753dd6bf232 (MD5) / Made available in DSpace on 2017-06-29T12:30:09Z (GMT). No. of bitstreams: 1 saramalagutiandradesoares.pdf: 1936313 bytes, checksum: bac06dfaa717be34b6dd2753dd6bf232 (MD5) Previous issue date: 2016-03-01 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / A obesidade é motivo de preocupação para a saúde pública em todo o mundo. Apesar de existirem muitos estudos sobre seu impacto no sistema imunológico, a influência nas doenças infecciosas é pouco relatado. A incidência da obesidade vem aumentando em países em desenvolvimento, assim é de grande importãncia o estudo do papel da obesidade na resposta imunológica a patógenos, principalmente em doenças infecciosas de grande relevãncia como a malaria. A obesidade é caracterizada por uma inflamação sistêmica de baixo grau crõnica, e acredita-se que as manifestações complicadas da malária, como a malaria cerebral, injuria respiratória, denominada malária grave, podem ser resultado da resposta inflamatória exagerada causada pelo sequestro de hemácias infectadas nos vasos endoteliais de orgãos vitais como cérebro e pulmão. Portanto a inflamação na obesidade pode alterar o curso da infecção do Plasmodium berguei ANKA, parasitas causadores da malária cerebral em modelo murino. Neste trabalho, investigamos a influência da obesidade na resposta imune frente à infecção por Plasmodium berguei ANKA. Para isso foram utilizados camundongos C57BL/6 machos, com idade de 4 a 6 semanas, alimentados durante 12 semanas por uma dieta hiperlipídica com 60% das quilocalorias advindas de lipídeos. Após esse período os animais foram infectados com a cepa ANKA de Plasmodium berguei. Nos animais alimentados com a dieta hiperlipídica, observou-se aumento do peso corporal, assim como da gordura perigonadal dos animais alimentados pela dieta hiperlipídica, sem aumento do consumo de ração. A resistência ao desenvolvimento da malária grave foi observada nos animais obesos; além de conseguir controlar a parasitemia, . Somente esses animais sobreviveram à infecção, por 25 dias após o desafio, sem apresentar sintomas clínicos da doença, ao contrário, os não obesos infectados, vieram a óbito após oito dias de infecção. Foram observadas diferenças no perfil celular dos animais obesos infectados quando comparados aos controles infectados, sugerindo que a inflamação prévia dos animais obesos pode ter influenciado o curso da infecção. Assim, os resultados indicam que alterações na resposta imunológica do camundongo obeso conseguem protege-lo contra o desenvolvimento da malaria grave. / Obesity is a public heaith concern currentiy affecting worldwide, aithough there are many studies on the impact of obesity on the immune system, the various aspects of the association between obesity and infection is seidom reported. The incidence of obesity is increasing in the developing countries, and it is very important to study the role of obesity in the immune response to pathogens, especially infectious diseases such as maiaria. Obesity is characterized by a iow-grade, systemic, chronic infiammation and it is believed that the complicated manifestations of maiaria, as severe maiaria, can be the result of an exaggerated inflammatory response caused by sequestration of infected erythrocytes to endothelial vesseis of vital organs such as brain and lung. So infiammation in obesity may alter the course of infection of Plasmodium berguei ANKA, parasites that cause cerebral maiaria in mice. In this work, we investigated the influence of obesity on the immune response to infection by Plasmodium berguei ANKA. For this, mate C57BL/6 mice aged 4 to 6 weeks were used, fed by a high fat diet with 60% of kilocalories from lipid, for 12 weeks. After this period the animais were infected with the strain ANKA of Plasmodium berguei. There was an increase in body weight as well as the perigonadal fat in animais fed with the high fat diet, without increasing the food intake, from the second week of dieting. The resistance to the deveiopment of severe maiaria was observed in the obese animais, beside of control the parasitemia, oniy those animais survived the infection for 25 days post challenge, without any clinicai symptoms of the disease, unlike infected non obese, who died after eight days of infection. Differences were observed in the cell profile of infected obese animais compared to infected controls, suggesting that prior infiammation in obese animais may have infiuenced the course of infection. Thus, the resuits indicate that changes in the immune response of obese mice can protect against the deveiopment of severe maiaria.

L’artésunate est désormais le traitement de référence du paludisme grave au plan mondial. Cependant, des cas d’anémie hémolytique différée ont été décrits chez 20% à 25% des voyageurs traités. L’épisode hémolytique survient 2 à 3 semaines après traitement. Environ la moitié des patients vont nécessiter une transfusion sanguine. L’artésunate induit un phénomène original en physiologie humaine : le “pitting” ou épépinage splénique des érythrocytes parasités. Il consiste en l’expulsion du parasite mort de l’érythrocyte hôte lorsque celui-ci traverse une structure microcirculatoire splénique appelée « fente interendothéliale ». Ces érythrocytes pittés retournent sans destruction immédiate dans la circulation générale. Nous avons étudié l’efficacité et la tolérance de l’artésunate intraveineux chez 123 voyageurs atteints de paludisme grave. Cent dix-sept patients ont survécu (95%). Parmi 78 patients suivis plus de 8 jours, 76 (97%) ont eu une anémie au cours du suivi et 21 une hémolyse différée typique (27%). Dans ce sous groupe de patients la chute médiane en hémoglobine a été de 1,3g/dl avec un nadir <7g/dl dans 15% des cas. Un seul patient a été transfusé. Le marquage de la protéine parasitaire Resa, véritable empreinte de l’infection érythrocytaire par Plasmodium falciparum, permet la visualisation des érythrocytes pittés. Chez 21 patients non transfusés le pic de concentration en érythrocytes pittés est survenu durant la première semaine. Chez 9 patients évoluant vers une hémolyse différée le pic de pittés était significativement plus élevé que chez 12 patients présentant d’autres profils évolutifs d’anémie (0,30 vs. 0,07 ; P = 0,0001). Une concentration d’érythrocytes pittés au pic supérieure à 180 millions/l aurait prédit le risque d’hémolyse différée avec une sensibilité de 89% et une spécificité de 83%. Utilisant la technologie ImageStream* l’étude morphologique érythrocytaire chez 4 patients a montré que l’infection plasmodiale suivi de pitting entraine une réduction de surface projetée de 8,9%. Cette altération pourrait contribuer à la réduction de la durée de vie des érythrocytes pittés. La destruction différée des érythrocytes infectés et épargnés par le pitting durant le traitement par artésunate est un mécanisme original d’anémie hémolytique. Ce travail a permis de structurer l’espace nosologique de l’anémie post-thérapeutique au cours du paludisme, de clarifier la physiopathologie de l’hémolyse différée et d’identifier certains de ses mécanismes. Malgré l’incidence élevée de l’hémolyse différée, l’anémie résultante n’est préoccupante que dans 15% des cas et ne remet pas en cause le bénéfice de l’artésunate par rapport à la quinine dans le traitement du paludisme grave. La concentration précoce des érythrocytes pittés pourrait être un marqueur prédictif intéressant de la survenue d’une hémolyse différée post-artésunate. / Worldwide, artesunate is now the recommended treatment for severe malaria. However cases of delayed hemolytic anemia have been described in 20% to 25% travelers treated with artesunate. The episode usually occurs 2 to 3 weeks after the end of the treatment. About half on the inpatients need blood transfusion. Artesunate induces an original phenomenon called splenic “pitting” of parasitized erythrocyte. The dead parasite is expelled from the host erythrocyte when it comes through a microcirculatory structure called inter-endothelial slit. These pitted red blood cells go back to the general blood circulation without destruction. We have studied efficacy and tolerance of intravenous artesunate in 123 patients with imported severe malaria, of whom 117 have survived (95%). Among 78 patients followed more than 8 days, 76 (97%) suffered from anemia during follow-up and 21 had a typical delayed hemolysis pattern (27%). In this sub group the median loss of hemoglobin was 1.3g/dl with a nadir below 7g/dl in 15% of them. Only one patient was transfused. The labelling of Resa protein, a plasmodium protein included in the bilayer membrane of the red blood cell, allowed the visualization of pitted cells. In 21 patients non transfused, the pitted cells peak occured during the first week post treatment. In 9 patients with typical delayed hemolysis pattern, the pitted cells peak was higher than in the 12 patients with other kind of anemia patterns (0.30 vs. 0.07 ; P = 0.0001). A pitted cells concentration above 180 millions/l would have predicted the risk of late hemolysis with 89% sensitivity and 83% specificity. Red blood cell morphology was studied using ImageStream* technology in 4 patients. It has shown that infection and pitting process induces a membrane projected area loss of 8.9%. This loss could explain the reduced life span of the pitted red blood cells. Differed destruction of the erythrocytes first infected and then spared by pitting process during the treatment with artesunate is a new pattern of hemolytic anemia during malaria. This work has provided a nosological framework of post therapy hemolysis during malaria, a clarified pathophysiology of delayed hemolysis and has identified potential explanatory mechanisms. Notwithstanding the high incidence of hemolysis, the resulting anemia is severe in 15% of the patients and does not jeopardize the advantage of artesunate compared to quinine in the treatment of severe malaria. Early pitted cells concentration could be a surrogate marker to determine the risk of delayed hemolysis and anemia after artesunate treatment.

Os genes var de Plasmodium falciparum codificam a proteína PfEMP1 expressa na superfície de eritrócitos infectados e que medeia os fenômenos de citoaderência e \"rosetting\". Ambos os fenômenos estão diretamente associados à malária grave, e seu domínio mais N-terminal, DBL1alfa, media especificamente \"rosetting\". Análise de seqüências DBL1alfa de isolados brasileiros e de outros países revelou que a similaridade entre elas não pode predizer origem geográfica. Com o objetivo de determinar se existem seqüências DBL1alfa associadas à malária grave, analisamos as seqüências DBL1alfa expressas em parasitas obtidos de pacientes brasileiros com esta manifestação clínica e encontramos que as seqüências predominantemente expressas apresentavam uma ou duas deleções de cisteínas. Significativamente, apesar de freqüentes no genoma de parasitas de pacientes com malária não grave, essas seqüências foram raramente expressas. Esses dados demonstram a primeira associação de seqüências PfEMP1 expressas e malária grave em pacientes da Amazônia Brasileira. / Plasmodium falciparum var genes code for PfEMP1, a protein expressed on the surface of infected erythrocytes, and which mediates cytoadherence and rosetting. Both phenomena are directly associated with severe malaria and the most N-terminal domain, DBL1alfa, specifically mediates rosetting. DBL1alfa sequence analysis from Brazilian and worldwide isolates revealed that sequence similarities cannot predict geographical origin. To determine whether there are DBL1alfa sequences associated with severe malaria, we examined expressed var DBL1alfa sequences in patients with severe malaria from the Brazilian Amazon and found that the predominantly expressed DBL1alfa sequences from these parasites lacked 1-2 cysteine residues. Significantly, these sequences were amply found on the genomic repertoire of parasites from patients with mild malaria and yet they were rarely expressed. These data demonstrate the first association of particular PfEMP1 expressed sequences and severe malaria in patients from the Brazilian Amazon.

Os genes var de Plasmodium falciparum codificam a proteína PfEMP1 expressa na superfície de eritrócitos infectados e que medeia os fenômenos de citoaderência e \"rosetting\". Ambos os fenômenos estão diretamente associados à malária grave, e seu domínio mais N-terminal, DBL1alfa, media especificamente \"rosetting\". Análise de seqüências DBL1alfa de isolados brasileiros e de outros países revelou que a similaridade entre elas não pode predizer origem geográfica. Com o objetivo de determinar se existem seqüências DBL1alfa associadas à malária grave, analisamos as seqüências DBL1alfa expressas em parasitas obtidos de pacientes brasileiros com esta manifestação clínica e encontramos que as seqüências predominantemente expressas apresentavam uma ou duas deleções de cisteínas. Significativamente, apesar de freqüentes no genoma de parasitas de pacientes com malária não grave, essas seqüências foram raramente expressas. Esses dados demonstram a primeira associação de seqüências PfEMP1 expressas e malária grave em pacientes da Amazônia Brasileira. / Plasmodium falciparum var genes code for PfEMP1, a protein expressed on the surface of infected erythrocytes, and which mediates cytoadherence and rosetting. Both phenomena are directly associated with severe malaria and the most N-terminal domain, DBL1alfa, specifically mediates rosetting. DBL1alfa sequence analysis from Brazilian and worldwide isolates revealed that sequence similarities cannot predict geographical origin. To determine whether there are DBL1alfa sequences associated with severe malaria, we examined expressed var DBL1alfa sequences in patients with severe malaria from the Brazilian Amazon and found that the predominantly expressed DBL1alfa sequences from these parasites lacked 1-2 cysteine residues. Significantly, these sequences were amply found on the genomic repertoire of parasites from patients with mild malaria and yet they were rarely expressed. These data demonstrate the first association of particular PfEMP1 expressed sequences and severe malaria in patients from the Brazilian Amazon.

Inhibition of nitric oxide (NO) signalling may contribute to the pathogenesis of severe malaria. This thesis examines the impact of Plasmodium infection on three key determinants of nitric oxide synthase (NOS) biochemistry: substrate availability, substrate/inhibitor homeostasis and cofactor availability. Arginine, the NOS substrate, is depleted in human patients with severe Plasmodium falciparum malaria and mice infected with P. berghei ANKA. Using heavy isotope tracer infusions to quantify arginine metabolism in infected mice, we found no evidence of increased catabolism by the enzyme arginase, widely assumed to be responsible for arginine depletion. Genetic knock-out of parasite arginase had no effect on arginine depletion in mice. Instead, our findings link arginine depletion to decreased rates of arginine and citrulline appearance in the plasma of infected mice. Asymmetric dimethylarginine (ADMA) competes with arginine for binding to the NOS catalytic site. We observed elevation of the ADMA/arginine ratio in Gambian children with severe malaria, favouring NOS inhibition. In mice infected with P. berghei ANKA, we found evidence of degradation of dimethylarginine dimethylaminohydrolase 1 (DDAH1), the enzyme primarily responsible for ADMA metabolism. We also observed reduced DDAH activity and accumulation of intracellular ADMA in hepatic tissue of infected mice, suggesting that DDAH dysfunction could contribute to disruption of ADMA/arginine homeostasis. Tetrahydrobiopterin (BH4) is an essential NOS cofactor. In P. berghei ANKA-infected mice, BH4 concentrations were decreased in plasma, erythrocytes and brain tissue, which could inhibit NO synthesis and promote NOS-dependent superoxide production. To reverse deficiencies of NOS substrate and cofactor availability, we infused P. berghei ANKA-infected mice with citrulline, an arginine precursor, and sepiapterin, a BH4 precursor. Restoration of systemic arginine and BH4 availability in infected mice improved whole blood nitrite concentrations, a biomarker of NO synthesis, but did not prevent onset of disease symptoms. These studies have identified biochemical disturbances that may contribute to severe malaria pathogenesis by inhibiting NO synthesis.

Le paludisme est une infection parasitaire de répartition mondiale notamment en zones intertropicales où l’infection par Plasmodium falciparum est responsable de centaines de milliers de morts par an principalement chez les enfants de moins de cinq ans. Le paludisme constitue également un problème en France par l’importation de cas de paludisme chez le voyageur de retour de zone d’endémie. L’infection à Plasmodium falciparum dans cette population, considérée comme à risque de développer les formes graves de la maladie, peut se présenter sous différentes formes cliniques plus ou moins associées au risque de mortalité. Même si certains facteurs de risque de gravité tels que l’âge et l’immunité ont été identifiés, cette interaction complexe hôte-parasite n’a été largement étudiée que chez l’enfant en zone d’endémie et peu de données sont disponibles pour le paludisme d’importation. L’objectif de ces travaux de thèse repose sur l’analyse des facteurs d’hôte et des facteurs parasitaires intervenant dans le paludisme d’importation. A travers le réseau de surveillance du centre national de référence du paludisme en France métropolitaine, l’ensemble des données démographiques, épidémiologiques, cliniques et biologiques des cas de paludisme d’importation, notifiés entre 2011 et 2015, ont été collectées ainsi que les échantillons ayant servis au diagnostic. Après expertise diagnostique, le plasma obtenu après centrifugation a été utilisé pour les dosages des antipaludéens, pour la quantification d’HRP2 ainsi que pour la sérologie anti-palustre. L’ARN extrait par le TRIZOL® à partir du culot globulaire a été utilisé pour l’étude de l’expression des gènes var et des domaines cassettes par qRT-PCR. Le culot de globules rouges parasités a été mis en culture pour la maturation des formes parasitaires en vue de l’étude du phénotype de cytoadhérence sur les récepteurs solubles CD36, ICAM-1, EPCR et du phénomène de rosetting . L’ensemble de ces études a été réalisé sur une population de patients dans le cadre du paludisme d’importation groupée en migrants de première génération, migrants de deuxième génération et voyageurs/expatriés et dont la présentation clinique du paludisme d’importation a été classée en paludisme « très grave », paludisme « grave » et paludisme « simple ». L’ensemble des données épidémiologiques, cliniques et biologiques recueillies au cours de l’étude a permis d’identifier l’âge élevé, l’origine ethnique, la profondeur de la thrombopénie et l’absence d’antécédents de paludisme comme des facteurs de risque associés à la survenue d’un accès palustre « très grave », entité clinique caractérisée pour une biomasse parasitaire séquestrée élevée. L’effet de la pré-exposition au parasite, reflété par le statut sérologique des patients, semble être à l’origine de la présentation clinique de la maladie en limitant notamment la biomasse parasitaire séquestrée au cours de l’accès palustre. L’étude de l’expression des gènes var et des domaines cassettes réalisée dans cette population, en fonction de la présentation clinique, de l’origine ethnique et du statut sérologique des patients, a révélé une surexpression du groupe de gènes var A et B et des motifs protéiques composant les domaines cassettes DC4, DC8 et DC13 dans le paludisme « grave » et « très grave » d’importation au sein de cette population hétérogène de patients. L’étude du phénotype de cytoadhérence et du rosetting, réalisée dans un autre groupe de patients rencontré dans le cadre du paludisme d’importation, a identifié le rosetting comme le phénotype d’adhérence à l’origine de l’accès palustre « très grave ». Le profil d’expression des gènes var et domaines cassettes correspondants à cette population a confirmé les observations antérieures et corrèle le phénotype de rosetting à l’expression des motifs protéiques DBLß3 et DBLa2 de DC4 et DC8 (...) / Malaria is a worldwide parasitic infection especially in tropical area where Plasmodium falciparum infection is responsible for hundreds of thousands annually mainly among children under five years old. Malaria is also a problem in France by the importation of malaria cases in travelers coming from endemic area. The Plasmodium falciparum infection in this population, considered at risk of developping severe malaria, can present different clinical forms more or less associated with mortality.While some risk factors for severity like age and immunity have been identified, this complex host-parasite interactions have been widely studied in children in endemic areas and few data are available for imported malaria. The aim of the thesis work is based on analysis of host factors and parasite factors in imported malaria.Through the monitoring network of the French National reference center of malaria, all the demographic, epidemiological, clinical and laboratory of imported malaria cases, notified between 2011 and 2015, were collected and also samples of the parasitological diagnosis. After diagnostic expertise, the plasma obtained after centrifugation was used for determinations of antimalarial drugs, for quantification of plasmatic HRP2 and for serological tests. RNA extracted by the Trizol® from red cells pellets was used to study the expression of var genes and domain cassettes by qRT-PCR. The pellet of parasitized red blood cells were cultured for maturation of parasitic forms for the study of phenotype cytoadherence on soluble receptor CD36, ICAM-1 and EPCR and for the study of the rosetting phenomenon. All of these studies was conducted in an imported malaria context,in a population of patients composed by first-generation migrants, second-generation migrants and travelers / expatriates and whose clinical presentation of imported malaria was classified into very severe (VSM), mild severe (MSM) and uncomplicated malaria (UM).All the epidemiological, clinical and biological data collected during the study identified the high age, ethnicity, depth of thrombocytopenia and no history of malaria as factors risk associated with the occurrence of very severe malaria, clinical entity characterized by high sequestered parasite biomass. The effect of pre-exposure to the parasite, reflected by the serological status of patients, seems to be the cause of the clinical presentation of the disease in particular by limiting parasite biomass sequestered during malaria. The study of the expression of var genes and domain cassettes performed in this population, according to clinical presentation, ethnicity and the serological status of patients, revealed an overexpression of the group of var genes A and B and protein patterns of the domain cassette DC4, DC8 and DC13 in mild severe and very severe malaria within this heterogeneous patient population. The study of cytoadherence phenotype and rosetting, made in another group of patients in imported malaria context, identified the rosetting as adhesion phenotype causing very severe malaria. The expression profile of var genes and domain cassettes corresponding to this population confirmed earlier observations and correlates rosetting phenotype to the expression of DBLß3 and DBLa2 of DC4 and DC8 (...)