Parasite Molecular Immunology - CNRS URA 2581  


  HEADDr Mercereau-Puijalon Odile / omp@pasteur.fr
  MEMBERSDr Barale J-C / Dr Bonnefoy S / Dr David P / Dr Durand R/ Dr Fandeur T / Dr Safeukui I / Dr Vigan I / Dr Brousse V / Dr Mohandas N / Deplaine G / Bouillon A / Gorgette O / Knight R / Guillotte M / Vallieres C / Ravaoarisoa E / Zamanka Naroua H/ Dupiat A


  Annual Report

The Unit's activities focus on Plasmodium falciparum blood stages. We investigate parasite virulence factors along three major lines of research: 1. parasite virulence factors remodelling the host red blood cell membrane ; 2. the mechanisms of parasite retention and clearance by the human spleen; 3. the parasite response to artemisinins and the rationale development of novel anti-malarials.

Parasite virulence factors : RESA and rosetting

Throughout its intracellular life within the red blood cell (RBC), P. falciparum remodels its host cell and exports proteins that either interact with the RBC cytoskeleton or are surface-exposed. This remodelling has important physiologic, mechanistic and serologic consequences.

PfRESA is discharged during invasion to the RBC membrane and interacts with spectrin. Reverse genetics, imaging and nanomechanics showed that PfRESA is essential to overcome the adverse consequences of exposure to febrile temperatures and contributes to the decreased deformability of ring-infected RBCs [1]. Similar strategies are used to unravel the biological role of the other two paralogs of the resa family, one of which is consistently overexpressed in patients.

The PfEMP1varO variant surface adhesin is exported by mature parasite stages to the RBC surface, where it mediates binding of uninfected RBCs (rosetting) and forms autoagglutinates. These particular cytoadherence phenotypes have been associated with severe malaria in African children. Studies in the Saimiri monkey showed that varO rosetting contributes to increased multiplication rate in vivo. Recombinant proteins expressing individual PfEMP1VarO domains in their native conformation were produced in the baculovirus system and used to generate surface-reacting specific antisera and mouse mAbs. By panning with specific mAbs, we developed a "single variant" in vitro model with virtually all parasites expressing the varO adhesin. Seroprevalence to this single variant varO clonal line was studied at the village level in a holoendemic setting (Dielmo, Senegal). Prevalence of antibodies reacting with the surface of varO infected RBC and to the recombinant domain (s) was very high [2]. Current work includes unravelling the molecular interactions involved in rosetting, investigation of acquisition of specific antibodies in populations living in distinct malaria-endemic areas and analysis of serological cross-reactivity.

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

The spleen is critical for the control of parasite biomass in infected patients, but the exact physiology of parasite handling by the spleen is unknown. We have established an experimental isolated-perfused human spleen system, functionally validated by the efficient processing of artesunate-killed infected RBCs [3]. Perfusion of RBCs infected with untreated, live parasites in the absence of specific antibodies showed that as predicted, mature stages were rapidly sequestered mainly due to cytoadherence to the splenic vascular endothelium. Unexpectedly, numerous young ring stages were retained as well, and accumulated upstream from inter-endothelial slits of the red pulp that challenge RBC deformability. The mild but significantly reduced elongation index of rings suggests an innate retention process linked to their modified mechanical properties [4].

The parasite response to artemisinin

Artemisinin derivatives are the cornerstone of currently recommended combination therapies and maintaining their efficacy is of prime importance for malaria control. 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 which of these changes reflect a defence of the parasite to the injury inflicted by artemisinin treatment or correspond to a pathway to parasite death.

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.

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



  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. Effect of plasmodial RESA protein on deformability of human red blood cells harboring Plasmodium falciparum. Proc Nat Acad Sci USA 2007, 104 (22): 9213-9217

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. 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. 2008 Sep 22. PMID: 18809668

Buffet PA, Milon G, Brousse V, Correas JM, Dousset B, Couvelard A, Kianmanesh R, Farges O, Sauvanet A, Paye F, Ungeheuer MN, Ottone C, Khun H, Fiette L, Guigon G, Huerre M, Mercereau-Puijalon O, David PH. 2006. Ex-vivo perfusion of human spleens maintains clearing and processing functions Blood, May 1;107(9):3745-52. PMID: 16384927

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. Retention of Plasmodium falciparum ring-infected erythrocytes in the slow, open microcirculation of the human spleen. Blood. 2008 Sep 15;112(6):2520-8. PMID: 18579796

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. Dynamic RNA profiling in Plasmodium falciparum synchronized blood stages exposed to lethal doses of artesunate. BMC Genomics. 2008 Aug 18;9:388. PMID: 18706115





Activity Reports 2009 - Institut Pasteur
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