Immunogenicity of the Plasmodium falciparum PfEMP1-VarO Adhesin: Induction of Surface-Reactive and Rosette-Disrupting Antibodies to VarO Infected Erythrocytes

PLoS One. 2015 Jul 29;10(7):e0134292. doi: 10.1371/journal.pone.0134292. eCollection 2015.

Abstract

Adhesion of Plasmodium falciparum-infected red blood cells (iRBC) to human erythrocytes (i.e. rosetting) is associated with severe malaria. Rosetting results from interactions between a subset of variant PfEMP1 (Plasmodium falciparum erythrocyte membrane protein 1) adhesins and specific erythrocyte receptors. Interfering with such interactions is considered a promising intervention against severe malaria. To evaluate the feasibility of a vaccine strategy targetting rosetting, we have used here the Palo Alto 89F5 VarO rosetting model. PfEMP1-VarO consists of five Duffy-Binding Like domains (DBL1-5) and one Cysteine-rich Interdomain Region (CIDR1). The binding domain has been mapped to DBL1 and the ABO blood group was identified as the erythrocyte receptor. Here, we study the immunogenicity of all six recombinant PfEMP1-VarO domains and the DBL1- CIDR1 Head domain in BALB/c and outbred OF1 mice. Five readouts of antibody responses are explored: ELISA titres on the recombinant antigen, VarO-iRBC immunoblot reactivity, VarO-iRBC surface-reactivity, capacity to disrupt VarO rosettes and the capacity to prevent VarO rosette formation. For three domains, we explore influence of the expression system on antigenicity and immunogenicity. We show that correctly folded PfEMP1 domains elicit high antibody titres and induce a homogeneous response in outbred and BALB/c mice after three injections. High levels of rosette-disrupting and rosette-preventing antibodies are induced by DBL1 and the Head domain. Reduced-alkylated or denatured proteins fail to induce surface-reacting and rosette-disrupting antibodies, indicating that surface epitopes are conformational. We also report limited cross-reactivity between some PfEMP1 VarO domains. These results highlight the high immunogenicity of the individual domains in outbred animals and provide a strong basis for a rational vaccination strategy targeting rosetting.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adhesins, Bacterial / chemistry
  • Adhesins, Bacterial / genetics
  • Adhesins, Bacterial / immunology*
  • Animals
  • Antibodies, Protozoan / blood
  • Antigens, Protozoan / chemistry
  • Antigens, Protozoan / genetics
  • Cross Reactions
  • Epitopes / chemistry
  • Epitopes / genetics
  • Erythrocytes / parasitology
  • Female
  • Humans
  • Malaria Vaccines / chemistry
  • Malaria Vaccines / genetics
  • Malaria Vaccines / immunology
  • Malaria, Falciparum / immunology
  • Malaria, Falciparum / parasitology
  • Malaria, Falciparum / prevention & control
  • Mice
  • Mice, Inbred BALB C
  • Plasmodium falciparum / genetics
  • Plasmodium falciparum / immunology*
  • Plasmodium falciparum / pathogenicity
  • Protein Structure, Tertiary
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / genetics
  • Protozoan Proteins / immunology*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / immunology
  • Rosette Formation

Substances

  • Adhesins, Bacterial
  • Antibodies, Protozoan
  • Antigens, Protozoan
  • Epitopes
  • Malaria Vaccines
  • Protozoan Proteins
  • Recombinant Proteins
  • erythrocyte membrane protein 1, Plasmodium falciparum

Grants and funding

This work was supported by the French National Research Agency (www.agence-nationale-recherche.fr/) (Agence Nationale de la Recherche, Programme Microbiologie, Immunologie et Maladies Emergentes, grant ANR-07-MIME-021-0, Project Rosettes, PIs OMP and GAB), which supported a fellowship to A. J. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement N° Evimalar 242095. OMP is a member of the Evimalar Network of Excellence (www.evimalar.org). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.