title: Wide cross-reactivity between Anopheles gambiae and Anopheles funestus SG6 salivary proteins supports exploitation of gSG6 as a marker of human exposure to major malaria vectors in tropical Africa.
abstract: BACKGROUND
  The Anopheles gambiae gSG6 is an anopheline-specific salivary protein which helps female mosquitoes to efficiently feed on blood. Besides its role in haematophagy, gSG6 is immunogenic and elicits in exposed individuals an IgG response, which may be used as indicator of exposure to the main African malaria vector A. gambiae. However, malaria transmission in tropical Africa is sustained by three main vectors (A. gambiae, Anopheles arabiensis and Anopheles funestus) and a general marker, reflecting exposure to at least these three species, would be especially valuable. The SG6 protein is highly conserved within the A. gambiae species complex whereas the A. funestus homologue, fSG6, is more divergent (80% identity with gSG6). The aim of this study was to evaluate cross-reactivity of human sera to gSG6 and fSG6.
  
  
  METHODS
  The A. funestus SG6 protein was expressed/purified and the humoral response to gSG6, fSG6 and a combination of the two antigens was compared in a population from a malaria hyperendemic area of Burkina Faso where both vectors were present, although with a large A. gambiae prevalence (>75%). Sera collected at the beginning and at the end of the high transmission/rainy season, as well as during the following low transmission/dry season, were analysed.
  
  
  RESULTS
  According to previous observations, both anti-SG6 IgG level and prevalence decreased during the low transmission/dry season and showed a typical age-dependent pattern. No significant difference in the response to the two antigens was found, although their combined use yielded in most cases higher IgG level.
  
  
  CONCLUSIONS
  Comparative analysis of gSG6 and fSG6 immunogenicity to humans suggests the occurrence of a wide cross-reactivity, even though the two proteins carry species-specific epitopes. This study supports the use of gSG6 as reliable indicator of exposure to the three main African malaria vectors, a marker which may be useful to monitor malaria transmission and evaluate vector control measures, especially in conditions of low malaria transmission and/or reduced vector density. The Anopheles stephensi SG6 protein also shares 80% identity with gSG6, suggesting the attractive possibility that the A. gambiae protein may also be useful to assess human exposure to several Asian malaria vectors.
authors.affiliation: Department of Public Health and Infectious Diseases, Sapienza University, P.le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Cinzia
authors.initials: C
authors.lastname: Rizzo
authors.forename: Raffaele
authors.initials: R
authors.lastname: Ronca
authors.forename: Gabriella
authors.initials: G
authors.lastname: Fiorentino
authors.forename: Valentina D
authors.initials: VD
authors.lastname: Mangano
authors.forename: Sodiomon B
authors.initials: SB
authors.lastname: Sirima
authors.forename: Issa
authors.initials: I
authors.lastname: Nèbiè
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Petrarca
authors.forename: David
authors.initials: D
authors.lastname: Modiano
authors.forename: Bruno
authors.initials: B
authors.lastname: Arcà
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000852:Anopheles / Q000737:chemistry*; D002050:Burkina Faso; D002648:Child; D002675:Child, Preschool; D003429:Cross Reactions; D004199:Disease Vectors; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007223:Infant; D019476:Insect Proteins / Q000276:immunology*; D008875:Middle Aged; D012471:Salivary Proteins and Peptides / Q000276:immunology*; D055815:Young Adult
chemical_list: D007074:Immunoglobulin G; D019476:Insect Proteins; D012471:Salivary Proteins and Peptides