Parasite Molecular Immunology - CNRS URA 2581  


  HEADDr Mercereau-Puijalon Odile / omp@pasteur.fr
  MEMBERSDr Barale J-C / Dr Bonnefoy S / Dr David P / Dr Ménard D/ Dr Safeukui I / Dr Vigan I / Dr Brousse V / Deplaine G / Bouillon A / Gorgette O / Guillotte M / Vallieres C / C. Dietrich/ S. Benakli / A. Worton/ Dupiat A


  Annual Report

The Unit's activities are centred on Plasmodium falciparumpathophysiology. Our research focuses on blood stages along the following lines: i) parasite factors remodelling the host cell membrane, ii) the mechanisms of parasite retention and clearance by the human spleen, iii) anti-malarial drug escape, and iv) drug discovery.

Parasite factors remodelling the red blood cell membrane: RESA and rosetting

The parasite remodels the RBC membrane very early after invasion, and the process is accentuated at the trophozoite stage. This remodelling has physiologic, mechanistic and serologic consequences that profoundly influence the survival of the parasite in its human host.

We study remodelling at the ring stage with a specific focus on attempting to reconstitute in the laboratory the physiological conditions to which parasites are naturally exposed, namely fever and frequent mechanical spleen challenge. This showed a dual role for the Ring Erythrocyte Surface Antigen (RESA), which is delivered to the RBC membrane cytoskeleton during invasion and interacts with the beta chain of spectrin. Reverse genetics, imaging and nanomechanics showed on the one hand that PfRESA is essential to withstand exposure of young ring stages to elevated temperatures and ensure normal parasite development subsequently. On the other hand, PfRESA-induced stabilization of the erythrocyte cytoskeleton decreases deformability of the Pf-RBC membrane of the ring stages, and particularly so at 41°C, possibly promoting their accelerated clearance.

Exploration of remodelling at the trophozoite stage focuses on rosetting, a cytoadherence phenotype consistently associated with severe malaria in African children.We have developed novel experimental approaches to obtain single variant cultures where parasites homogeneously express a single adhesin and work with the VarO model, where all parasites express the PfEMP1varO protein. Individual PfEMP1VarO recombinant domains in their native conformation were characterised and used to study seroprevalence in several endemic areas. Prevalence of antibodies reacting with the recombinant domains as well as prevalence of varO-infected RBC surface-reactive antibodies is very high, and associated with acquired protection.

Physiology of parasitism: retention and clearance of infected red blood cells by the spleen

One important role of the human spleen is the quality control of circulating RBCs. Identified factors influencing RBC and Pf-RBC clearance include cell deformability, RBC surface/volume ratio, exposure to antiparasitic drugs and specific humoral response. However, the tissue mechanisms of the spleen sorting/clearance function remain obscure. In order to explore this key partner in the host-parasite relationship, we established an isolated/perfused human spleen model system. We showed that both phagocytosis and pitting operate to clear artesunate-treated ring stages. Perfusion of live parasites in the absence of specific antibodies showed rapid clearance of mature forms, many of which cytoadhered to the splenic vascular endothelial lining. Unexpectedly, numerous young ring stages were retained as well, and accumulated upstream from inter-endothelial slits of the red pulp where considerable RBC deformation is needed for the cell to get back to circulation. The mild but significantly reduced elongation index of rings suggests an innate retention process linked to their modified mechanical properties.These observations generated a novel paradigm on the role of the spleen in malaria patients. The substantial retention of parasite young forms sheds new light on current models used for estimating parasite loads and suggests new hypothesis for pathophysiology of malaria.

The parasite response to artemisinin

Artemisinin derivatives are the cornerstone of currently recommended combination therapies and the emerging evidence for their reduced efficacy in Cambodia is of considerable concern. Little is known on the mode of action and on the parasite response to artemisinins. Analysis of the dynamic changes of the parasite transcriptome after exposure to lethal doses of artesunate in vitro shed interesting new light on the mobilization of processes shaping the interface between the parasite and its environment and interference with metabolic pathways [5]. We are currently investigating the contribution of some of these genes to the responses tending to overcome drug toxicity.

The biology of sub proteases and the rationale development of antimalarials

Parasite encoded subtilisin proteases implicated in the invasion process are promising novel drug targets. Current efforts concern elucidation of their biological function, characterisation of the catalytic properties of the parasite and recombinant enzymes, development of specific inhibitors using a combination of strategies and their validation using in vitro culture of P. falciparumand in vivo rodent malaria infection.

Keywords: red cell membrane, virulence, fever, clearance, antimalarials, spleen



  Publications

Mills JP, Diez-Silva M, Quinn DJ, Dao M, Tan KSW, Lim CT, Milon G, David PH, Mercereau-Puijalon O, Bonnefoy S, Suresh S. (2007) Effect of plasmodial RESA protein on deformability of human red blood cells harboring Plasmodium falciparum. Proc Nat Acad Sci USA, 104 (22): 9213-9217. PMID: 17517609

Natalang O, Bischoff E, Deplaine G, Proux C, Dillies MA, Sismeiro O, Guigon G, Bonnefoy S, Patarapotikul J, Mercereau-Puijalon O, Coppée JY, David PH. (2008) Dynamic RNA profiling in Plasmodium falciparum synchronized blood stages exposed to lethal doses of artesunate. BMC Genomics. 9:388. PMID: 18706115

Safeukui I, Correas JM, Brousse V, Hirt D, Deplaine G, Mulé S, Lesurtel M, Goasguen N, Sauvanet A, Couvelard A, Kerneis S, Khun H, Vigan-Womas I, Ottone C, Molina TJ, Tréluyer JM, Mercereau-Puijalon O, Milon G, David PH, Buffet PA. (2008) Retention of Plasmodium falciparum ring-infected erythrocytes in the slow, open microcirculation of the human spleen. Blood. 112(6):2520-8. PMID: 18579796

Vigan-Womas I, Guillotte M, Le Scanf C, Igonet S, Petres S, Juillerat A, Badaut C, Nato F, Schneider A, Lavergne A, Contamin H, Tall A, Baril L, Bentley GA, Mercereau-Puijalon O. (2008) An in vivo/in vitro model of Plasmodium falciparum rosetting and autoagglutination mediated by varO, a group A var gene encoding a frequent serotype. Infect Immun. 76(12): 5565-80. PMID: 18809668

Buffet PA, Safeukui I, Milon G, Mercereau-Puijalon O, David P.H. (2009) Retention of erythrocytes in the spleen: a double-edged process in human malaria. Curr Opin Hematol.16(3):157-64 PMID: 19384231

Noranate N, Prugnolle F, Jouin H, Tall A, Marrama L, Sokhna C, Ekala MT, Guillotte M, Bischoff E, Bouchier C, Patarapotikul J, Ohashi J, Trape JF, Rogier C, Mercereau-Puijalon O (2009). Population diversity and antibody selective pressure to Plasmodium falciparum MSP1 block2 locus in an African malaria-endemic setting. BMC Microbiol. 9(1):219. PMID: 19832989





Activity Reports 2009 - Institut Pasteur
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