Fig 4.

Neutralization activity analysis of CHIK-positive patient sera. (A) Neutralization activity of serum samples from 23 patients with chikungunya that were collected in Thailand from 2009 to 2012 was analyzed using the CHIKV-pseudotyped lentiviral vector. Four DEN-positive and two JE-positive serum samples collected in Thailand, as well as two healthy human serum samples, were used as controls. Pseudotyped lentiviral vectors were incubated with serially diluted serum and added to cells, and luciferase activity was measured. The percent inhibition rate was calculated relative to pooled healthy human serum plotted in the normal sample group. CHIK-positive sera, gray circles; control sera, white circles. Left, neutralization activity of serum samples diluted to 1:800. Error bars show the SEM of results from three independent experiments. Right, the data shown on the left were rearranged into control and sample groups; thick black lines show the grand mean. ***, P < 0.0001 (Student's t test). (B) Comparison between NT titers determined by NT assay using the CHIKV-pseudotyped lentiviral vector (Luc NT titer) and by a conventional assay using native CHIKV (NT titer). (C) Comparison between Luc NT titer and CHIKV antibody titer determined by ELISA (ELISA Ab titer).