Fig 2. Neutralizing antibodies of immune sera interact with the epitopes on E2 and E1-E2 glycoproteins.

(A) CHIKV antibody titer against recombinant E1 glycoprotein (100 ng) was determined in ELISA. The ELISA was performed at different serum dilutions using pooled sera. The dotted line represents the cut-off value (mean + 3SD) derived from healthy controls. (B) Competitive blocking assay was performed at 1:200 dilution in triplicate using 7 pools of ECSA and Asian sera, with similar neutralizing titers in each pool. Data are expressed as percentages of infectivity of an infection control, and are presented as means ± SEM. ***P< 0.001, repeated measures ANOVA with the Bonferroni multiple comparison test. (C) Schematic diagram showing the construction of chimera viruses with replacement of E2 or E1/E2 from SFV into the CHIKV ICRES1 backbone. Seroneutralization was performed against the chimera constructs and the percentage of infectivity was compared to that obtained with ICRES1. Data are represented as means ± SD from 4 independent experiments at a serum dilution of 1:100 (pooled sera). ***P<0.01, Kruskal-Wallis test. G, genomic promoter; SG, subgenomic promoter.