FIG 6.

JEV(M-I36F) is attenuated in vivo and induces the production of JEV neutralizing antibodies in mice. (A) Groups of 3-week-old C57BL/6 mice (6 per group) were monitored for survival after intraperitoneal injection with various doses (10³ to 10⁶ FFU) of wild-type JEV (WT) or mutant JEV(M-I36F) (I36F). A representative experiment out of 2 repeats is shown. Asterisks indicate that the differences between survival curves are statistically significant when data are compared using the log-rank (Mantel-Cox) test (***, P < 0.001; **, 0.001 < P < 0.01; *, 0.01 < P < 0.05; not significant, P > 0.05). (B) The neutralization activities against wild-type live JEV of sera collected from C57BL/6 mice 23 days after inoculation with 10³ FFU of wild-type JEV (WT) or mutant JEV(M-I36F) (I36F) were evaluated using a standard FRNT assay in BHK-21 cells. Each symbol represents the FRNT₅₀ value obtained for an individual mouse. Asterisks indicate that the differences between experimental samples are statistically significant when data are compared using the unpaired t test (***, P < 0.001; **, 0.001 < P < 0.01; *, 0.01 < P < 0.05; not significant, P > 0.05).