title: Immunisation with recombinant PfEMP1 domains elicits functional rosette-inhibiting and phagocytosis-inducing antibodies to Plasmodium falciparum.
abstract: BACKGROUND
  Rosetting is a Plasmodium falciparum virulence factor implicated in the pathogenesis of life-threatening malaria. Rosetting occurs when parasite-derived P. falciparum Erythrocyte Membrane Protein One (PfEMP1) on the surface of infected erythrocytes binds to human receptors on uninfected erythrocytes. PfEMP1 is a possible target for a vaccine to induce antibodies to inhibit rosetting and prevent severe malaria.
  
  
  RESULTS
  We examined the vaccine potential of the six extracellular domains of a rosette-mediating PfEMP1 variant (ITvar9/R29var1 from the R29 parasite strain) by immunizing rabbits with recombinant proteins expressed in E. coli. Antibodies raised to each domain were tested for surface fluorescence with live infected erythrocytes, rosette inhibition and phagocytosis-induction. Antibodies to all PfEMP1 domains recognized the surface of live infected erythrocytes down to low concentrations (0.02-1.56 µg/ml of total IgG). Antibodies to all PfEMP1 domains except for the second Duffy-Binding-Like region inhibited rosetting (50% inhibitory concentration 0.04-4 µg/ml) and were able to opsonize and induce phagocytosis of infected erythrocytes at low concentrations (1.56-6.25 µg/ml). Antibodies to the N-terminal region (NTS-DBL1α) were the most effective in all assays. All antibodies were specific for the R29 parasite strain, and showed no functional activity against five other rosetting strains.
  
  
  CONCLUSIONS
  These results are encouraging for vaccine development as they show that potent antibodies can be generated to recombinant PfEMP1 domains that will inhibit rosetting and induce phagocytosis of infected erythrocytes. However, further work is needed on rosetting mechanisms and cross-reactivity in field isolates to define a set of PfEMP1 variants that could induce functional antibodies against a broad range of P. falciparum rosetting parasites.
authors.affiliation: Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Ashfaq
authors.initials: A
authors.lastname: Ghumra
authors.forename: Pongsak
authors.initials: P
authors.lastname: Khunrae
authors.forename: Ricardo
authors.initials: R
authors.lastname: Ataide
authors.forename: Ahmed
authors.initials: A
authors.lastname: Raza
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Rogerson
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Higgins
authors.forename: J Alexandra
authors.initials: JA
authors.lastname: Rowe
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000096:biosynthesis* / Q000276:immunology; D004912:Erythrocytes / Q000469:parasitology; D006801:Humans; D007114:Immunization / Q000379:methods*; D010587:Phagocytosis; D010963:Plasmodium falciparum / Q000276:immunology*; D015800:Protozoan Proteins / Q000008:administration & dosage / Q000276:immunology / Q000627:therapeutic use*; D011817:Rabbits; D011994:Recombinant Proteins; D012397:Rosette Formation
chemical_list: D000913:Antibodies, Protozoan; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C085731:erythrocyte membrane protein 1, Plasmodium falciparum