title: Measuring naturally acquired immune responses to candidate malaria vaccine antigens in Ghanaian adults.
abstract: BACKGROUND
  To prepare field sites for malaria vaccine trials, it is important to determine baseline antibody and T cell responses to candidate malaria vaccine antigens. Assessing T cell responses is especially challenging, given genetic restriction, low responses observed in endemic areas, their variability over time, potential suppression by parasitaemia and the intrinsic variability of the assays.
  
  
  METHODS
  In Part A of this study, antibody titres were measured in adults from urban and rural communities in Ghana to recombinant Plasmodium falciparum CSP, SSP2/TRAP, LSA1, EXP1, MSP1, MSP3 and EBA175 by ELISA, and to sporozoites and infected erythrocytes by IFA. Positive ELISA responses were determined using two methods. T cell responses to defined CD8 or CD4 T cell epitopes from CSP, SSP2/TRAP, LSA1 and EXP1 were measured by ex vivo IFN-γ ELISpot assays using HLA-matched Class I- and DR-restricted synthetic peptides. In Part B, the reproducibility of the ELISpot assay to CSP and AMA1 was measured by repeating assays of individual samples using peptide pools and low, medium or high stringency criteria for defining positive responses, and by comparing samples collected two weeks apart.
  
  
  RESULTS
  In Part A, positive antibody responses varied widely from 17%-100%, according to the antigen and statistical method, with blood stage antigens showing more frequent and higher magnitude responses. ELISA titres were higher in rural subjects, while IFA titres and the frequencies and magnitudes of ex vivo ELISpot activities were similar in both communities. DR-restricted peptides showed stronger responses than Class I-restricted peptides. In Part B, the most stringent statistical criteria gave the fewest, and the least stringent the most positive responses, with reproducibility slightly higher using the least stringent method when assays were repeated. Results varied significantly between the two-week time-points for many participants.
  
  
  CONCLUSIONS
  All participants were positive for at least one malaria protein by ELISA, with results dependent on the criteria for positivity. Likewise, ELISpot responses varied among participants, but were relatively reproducible by the three methods tested, especially the least stringent, when assays were repeated. However, results often differed between samples taken two weeks apart, indicating significant biological variability over short intervals.
authors.affiliation: Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana.
authors.forename: Daniel
authors.initials: D
authors.lastname: Dodoo
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hollingdale
authors.forename: Dorothy
authors.initials: D
authors.lastname: Anum
authors.forename: Kwadwo A
authors.initials: KA
authors.lastname: Koram
authors.forename: Ben
authors.initials: B
authors.lastname: Gyan
authors.forename: Bartholomew D
authors.initials: BD
authors.lastname: Akanmori
authors.forename: Josephine
authors.initials: J
authors.lastname: Ocran
authors.forename: Susan
authors.initials: S
authors.lastname: Adu-Amankwah
authors.forename: Harini
authors.initials: H
authors.lastname: Geneshan
authors.forename: Esteban
authors.initials: E
authors.lastname: Abot
authors.forename: Jennylyn
authors.initials: J
authors.lastname: Legano
authors.forename: Glenna
authors.initials: G
authors.lastname: Banania
authors.forename: Renato
authors.initials: R
authors.lastname: Sayo
authors.forename: Donald
authors.initials: D
authors.lastname: Brambilla
authors.forename: Sanjai
authors.initials: S
authors.lastname: Kumar
authors.forename: Denise L
authors.initials: DL
authors.lastname: Doolan
authors.forename: William O
authors.initials: WO
authors.lastname: Rogers
authors.forename: Judith
authors.initials: J
authors.lastname: Epstein
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Richie
authors.forename: Martha
authors.initials: M
authors.lastname: Sedegah
mesh_terms: D000293:Adolescent; D000328:Adult; D000913:Antibodies, Protozoan / Q000097:blood*; D000953:Antigens, Protozoan / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D058501:Enzyme-Linked Immunospot Assay; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D005869:Ghana; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D017780:Malaria Vaccines / Q000276:immunology; D016778:Malaria, Falciparum / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology; D015203:Reproducibility of Results; D012424:Rural Population; D013601:T-Lymphocytes / Q000276:immunology*; D014505:Urban Population; D055815:Young Adult
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D017780:Malaria Vaccines; D011994:Recombinant Proteins; D007371:Interferon-gamma