Dissection of the Role of PfEMP1 and ICAM-1 in the Sensing of Plasmodium falciparum-Infected Erythrocytes by Natural Killer Cells

BACKGROUND: Host innate immunity contributes to malaria clinical outcome by providing protective inflammatory cytokines such as interferon-γ, and by shaping the adaptive immune response. Plasmodium falciparum (Pf) is the etiologic agent of the most severe forms of human malaria. Natural Killer (NK) cells are lymphocytes of the innate immune system that are the first effectors to produce interferon-γ in response to Pf. However, the molecular bases of Pf-NK cell recognition events are unknown. Our study focuses on the role of Pf erythrocyte membrane protein 1 (PfEMP1), a major Pf virulence factor. PfEMP1 is expressed on parasitized-erythrocytes and participates to vascular obstruction through the binding to several host receptors. PfEMP1 is also a pivotal target for host antibody response to Pf infection. METHODOLOGY/PRINCIPAL FINDINGS: Using genetically-engineered parasite mutant strains, a human genetic deficiency, and blocking antibodies, we identified two receptor-ligand pairs involved in two uncoupled events occurring during the sensing of Pf infection by NK cells. First, PfEMP1 interaction with one of its host receptor, chondroitin sulfate A, mediates the cytoadhesion of Pf-infected erythrocytes to human NK cell lines, but is not required for primary NK cell activation. Second, intercellular adhesion molecule-1 (ICAM-1), another host receptor for PfEMP1, is mandatory for NK cell interferon-γ response. In this case, ICAM-1 acts via its engagement with its host ligand, LFA-1, and not with PfEMP1, consistent with the obligatory cross-talk of NK cells with macrophages for their production of interferon-γ. CONCLUSION/SIGNIFICANCE: PfEMP1-independent but ICAM-1/LFA-1-dependent events occurring during NK cell activation by Pf highlight the fundamental role of cellular cooperation during innate immune response to malaria

Etude du mouvement des vesicules du systeme endocytique dans des fibroblastes de souris, clone 1D, vivants, par recouvrement de fluorescence apres photoblanchiment

INIST T 76879 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Platelets reorient Plasmodium falciparum-infected erythrocyte cytoadhesion to activated endothelial cells.

Severe malaria is characterized by the sequestration of Plasmodium falciparum-infected erythrocytes (IEs). Because platelets can affect tumor necrosis factor (TNF)-activated endothelial cells (ECs), we investigated their role in the sequestration of IEs, using IEs that were selected because they can adhere to endothelial CD36 (IE(CD36)), a P. falciparum receptor that is expressed on platelets. The results of coincubation studies indicated that platelets can induce IE(CD36) binding to CD36-deficient brain microvascular ECs. This induced cytoadhesion resisted physiological shear stress, was increased by EC stimulation with TNF, and was abolished by anti-CD36 monoclonal antibody. Immunofluorescence and scanning electron microscopy results showed that platelets serve as a bridge between IEs and the surface of ECs and may therefore provide receptors for adhesion to microvascular beds that otherwise lack adhesion receptors. This novel mechanism of cytoadhesion may reorient the sequestration of different parasite phenotypes and play an important role in the pathogenesis of severe malaria

Neural Cell Adhesion Molecule, a New Cytoadhesion Receptor for Plasmodium falciparum-Infected Erythrocytes Capable of Aggregation▿

The cytoadhesion of Plasmodium falciparum-infected erythrocytes (IEs) to the endothelial cells lining the microvasculature, clogging the microvessels of various organs, is a key event in the pathogenesis of certain severe forms of malaria, such as cerebral malaria and pulmonary edema. Studies aiming to identify possible correlations between the severity of clinical cases and the presence of particular cytoadhesion phenotypes have been largely unsuccessful. One of the possible reasons for this failure is that some of the key receptors and/or mechanisms involved have yet to be identified. By combining IE selection, cell transfection, and adhesion inhibition assays, we identified a new cytoadhesion receptor, neural cell adhesion molecule (NCAM). NCAM is a member of the immunoglobulin superfamily and has nonpolysialylated and polysialylated isoforms, the latter being rare in adults. The nonpolysialylated form is present on the surfaces of endothelial cells in the microvessels of various organs in which IE sequestration occurs. We found that multiphenotypic IEs interacted with nonpolysialylated NCAM and with another, as yet unidentified receptor. These IEs also displayed cytoadhesion in flow conditions, presenting the unique ability to form adherent macroaggregates composed of hundreds of IEs. These features may act as virulence factors, increasing the capacity of IEs to clog microvessels via receptor synergy and macroaggregate formation, thereby facilitating the pathogenesis of severe forms of malaria

Sequestration of Plasmodium falciparum–infected erythrocytes to chondroitin sulfate A, a receptor for maternal malaria: monoclonal antibodies against the native parasite ligand reveal pan-reactive epitopes in placental isolates

International audienceLes parasites de Plasmodium falciparum expriment des molécules d'adhésion variant à la surface des érythrocytes infectés (IE), qui agissent comme des cibles de protection naturelle. Récemment, il a été démontré que la séquestration d'IE dans le placenta est médiée par la liaison au sulfate de chondroïtine A via le domaine de type duffy binding (DBL) -gamma 3 de la protéine membranaire 1 des érythrocytes de P. falciparum (PfEMP1 (CSA)). Les procédures d'immunisation conventionnelles aboutissent rarement à la production réussie d'anticorps monoclonaux (mAbs) contre de tels candidats vaccins conformationnels. Ici, nous montrons que cette difficulté peut être surmontée en rendant les cellules B de souris Balb / c tolérantes à la surface des érythrocytes humains ou des cellules ovariennes de hamster chinois (CHO) avant d'injecter P falciparum IEs ou des cellules CHO transfectées exprimant la liaison du sulfate de chondroïtine A (CSA) domaine (DBL-gamma 3) du gène FCR3 var (CSA). Nous avons fusionné des cellules de rate avec des cellules P3U1 et obtenu entre 20% et 60% mAbs qui marquent spécifiquement la surface des érythrocytes infectés matures du phénotype CSA (mIE (CSA)) mais pas d'autres phénotypes adhésifs. Étonnamment, 70,8% des 43 mAbs analysés dans ce travail étaient des IgM. Tous les mAbs immunoprécipités PfEMP1 (CSA) à partir d'extraits de (125) I IE marqué en surface (CSA). Plusieurs AcM se sont liés efficacement à la surface des parasites se liant à la CSA de différentes zones géographiques et aux isolats placentaires d'Afrique de l'Ouest. Les mAb à réactivité croisée sont dirigés contre le DBL-gamma 3 (CSA), démontrant que ce domaine, qui assure la liaison de la CSA, est capable d'induire une réponse immunitaire panréactive. Ce travail est une étape importante vers le développement d'un vaccin à base de DBL-gamma 3 qui pourrait protéger les femmes enceintes de la pathogenèse. )

Identification of ATP2B4 Regulatory Element Containing Functional Genetic Variants Associated with Severe Malaria

International audienceGenome-wide association studies for severe malaria (SM) have identified 30 genetic variants mostly located in non-coding regions. Here, we aimed to identify potential causal genetic variants located in these loci and demonstrate their functional activity. We systematically investigated the regulatory effect of the SNPs in linkage disequilibrium (LD) with the malaria-associated genetic variants. Annotating and prioritizing genetic variants led to the identification of a regulatory region containing five ATP2B4 SNPs in LD with rs10900585. We found significant associations between SM and rs10900585 and our candidate SNPs (rs11240734, rs1541252, rs1541253, rs1541254, and rs1541255) in a Senegalese population. Then, we demonstrated that both individual SNPs and the combination of SNPs had regulatory effects. Moreover, CRISPR/Cas9-mediated deletion of this region decreased ATP2B4 transcript and protein levels and increased Ca2+ intracellular concentration in the K562 cell line. Our data demonstrate that severe malaria-associated genetic variants alter the expression of ATP2B4 encoding a plasma membrane calcium-transporting ATPase 4 (PMCA4) expressed on red blood cells. Altering the activity of this regulatory element affects the risk of SM, likely through calcium concentration effect on parasitaemia