Figure 1.
Schematic representation of flavivirus particles and YF virus antigens used in this study.
(A) Schematic model of a flavivirus particle. Left panel: immature virion, right panel: mature virion. The capsid contains the viral RNA and multiple copies of the C protein. The surface of immature particles consists of 60 spikes composed of trimers of prM-E heterodimers. Mature particles are formed after prM cleavage and contain 90 E homodimers. The structure of E was determined for soluble forms of E (sE) - schematically shown in the panel of mature virions - lacking the so-called stem- and membrane anchor-regions. (B) Representation of the arrangement of E dimers at the surface of mature dengue 2 virions. Thirty rafts of three parallel E dimers form a herringbone-like icosahedral shell. The figure was constructed using the coordinates of dengue 2 virus from the VIPERdb Virus Particle Explorer (viperdb 1thd; http://viperdb.scripps.edu). (C) Schematic representations of recombinant yellow fever antigens. Color code E: domain I – red, domain II – yellow, domain III – blue; fusion peptide (FP) - orange; stem – purple; transmembrane anchor – light grey. Color code prM: ectodomain – green, transmembrane anchors – dark grey. Color code of recombinant protein tags: black. TR: thioredoxin. The asterisk indicates the position of the mutation in the furin cleavage site of YF prM.
Figure 2.
Characteristics of the YF post-vaccination cohort and sera.
Distribution of (A) age at the time of vaccination, (B) age at the time of sample collection, and (C) years between vaccination and sample collection. (D) Correlation of YF NT titers and years between vaccination and sample collection. The Pearson correlation coefficients r and the P values are indicated. (E) Comparison of YF NT titers of young (<30 years of age at the time of vaccination) and elderly (>50 years of age at the time of vaccination) vaccinees. Only individuals who were vaccinated within 3 years before sample collection were included. The statistical analysis is provided at the top of the panel (t-test; ns, not significant).
Table 1.
Characterization of cohort of YF vaccinees.
Figure 3.
ELISA reactivities and NT titers of YF post-vaccination sera.
Antibody ELISA reactivities against different antigens are expressed as IgG units. Dashed lines indicate the cut-off in each assay.
Table 2.
Correlation of results obtained in different YF antibody assays (Pearson correlation coefficients).
Figure 4.
ELISA reactivities and NT titers of YF post-vaccination sera ordered according to their virion ELISA reactivities.
ELISA IgG units obtained with YF virion (A), YF sE (B), YF DI+II (C) and prM (D). (E) YF virus-specific NT titers. Dashed lines indicate the cut-off in each assay. Numbers and asterisks on top of the columns indicate sera of vaccinees selected for depletion analyses (Table 3 and Figure 6).
Figure 5.
Extent of variation of antibody reactivities in YF post-vaccination sera.
The ratio of results obtained in the YF sE, YF DI+DII and YF prM ELISA as well as YF NT relative to virion ELISA results was calculated for all sera. Data are expressed as log2 of these ratios multiplied by 100 and each of the circles represents the ratio obtained for an individual serum.
Figure 6.
ELISA and NT analyses of YF post-immunization sera after depletion with YF sE (panels A), YF DI+II (panels B), YF DIII (panels C) and YF prM (panels D).
Left panels: Percent reactivity in post-depletion sera, determined by ELISA with the depletion antigen. Middle panels: Percent reactivity in post-depletion sera, determined by ELISA with the virion. Right panels: Percent reactivity in post-depletion sera, determined by NT. Results are expressed as percent of the ELISA IgG units or NT titers of mock-depleted sera (control). The numbers above the columns in the middle and right panels indicate the percentage of reactivities remaining after depletion. Asterisks indicate the significance of difference in antibody reactivities between depleted and control sera (t-test). The error bars represent standard error of the means calculated from the results of at least three independent assays. Identification numbers of vaccinees are indicated under the panels (compare with Table 3 and Figure 4).
Table 3.
Characteristics of sera selected for depletion.