title: Expression of a type B RIFIN in Plasmodium falciparum merozoites and gametes.
abstract: BACKGROUND
  The ability of Plasmodium falciparum to undergo antigenic variation, by switching expression among protein variants encoded by multigene families, such as var, rif and stevor, is key to the survival of this parasite in the human host. The RIFIN protein family can be divided into A and B types based on the presence or absence of a 25 amino acid motif in the semi-conserved domain. A particular type B RIFIN, PF13_0006, has previously been shown to be strongly transcribed in the asexual and sexual stages of P. falciparum in vitro.
  
  
  METHODS
  Antibodies to recombinant PF13_0006 RIFIN were used in immunofluorescence and confocal imaging of 3D7 parasites throughout the asexual reproduction and sexual development to examine the expression of PF13_0006. Furthermore, reactivity to recombinant PF13_0006 was measured in plasma samples collected from individuals from both East and West African endemic areas.
  
  
  RESULTS
  The PF13_0006 RIFIN variant appeared expressed by both released merozoites and gametes after emergence. 7.4% and 12.1% of individuals from East and West African endemic areas, respectively, carry plasma antibodies that recognize recombinant PF13_0006, where the antibody responses were more common among older children.
  
  
  CONCLUSIONS
  The stage specificity of PF13_0006 suggests that the diversity of RIFIN variants has evolved to provide multiple specialized functions in different stages of the parasite life cycle. These data also suggest that RIFIN variants antigenically similar to PF13_0006 occur in African parasite populations.
authors.affiliation: Centre for Medical Parasitology, Department of International Health, Immunology, and Microbiology, University of Copenhagen, Denmark.
authors.forename: Steven B
authors.initials: SB
authors.lastname: Mwakalinga
authors.forename: Christian W
authors.initials: CW
authors.lastname: Wang
authors.forename: Dominique C
authors.initials: DC
authors.lastname: Bengtsson
authors.forename: Louise
authors.initials: L
authors.lastname: Turner
authors.forename: Bismarck
authors.initials: B
authors.lastname: Dinko
authors.forename: John P
authors.initials: JP
authors.lastname: Lusingu
authors.forename: David E
authors.initials: DE
authors.lastname: Arnot
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Sutherland
authors.forename: Thor G
authors.initials: TG
authors.lastname: Theander
authors.forename: Thomas
authors.initials: T
authors.lastname: Lavstsen
mesh_terms: D000293:Adolescent; D000328:Adult; D000349:Africa / Q000453:epidemiology; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D000940:Antigenic Variation / Q000235:genetics; D000953:Antigens, Protozoan / Q000235:genetics; D001483:Base Sequence; D002648:Child; D002675:Child, Preschool; D016054:DNA, Protozoan / Q000235:genetics; D019353:Endemic Diseases; D005260:Female; D018507:Gene Expression Regulation, Developmental; D017125:Genes, Protozoan; D006790:Host-Parasite Interactions / Q000276:immunology; D006801:Humans; D007223:Infant; D016778:Malaria, Falciparum / Q000453:epidemiology / Q000276:immunology / Q000469:parasitology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000276:immunology*; D020066:Merozoite Surface Protein 1 / Q000378:metabolism; D052940:Merozoites / Q000276:immunology; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000235:genetics* / Q000254:growth & development / Q000276:immunology*; D015800:Protozoan Proteins / Q000235:genetics* / Q000276:immunology*; D055815:Young Adult
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D016054:DNA, Protozoan; D008565:Membrane Proteins; D020066:Merozoite Surface Protein 1; D015800:Protozoan Proteins; C534665:RIFIN protein, Plasmodium falciparum