FIG 2.

17D-IRES is highly attenuated in neurovirulence in BALB/c and A129 mice. Four-week-old A129 mice (A and B) and 3-week-old BALB/c mice (C and D) were i.c. inoculated with 10³ PFU of 17D or 17D-IRES. Survival curves of the animals were observed (A and C), and viral loads in mouse brains were determined by plaque assay (B and D). The limit of detection is shown as a dashed line with a value of 89 PFU/g. Data on the viral titer in the brain represent the means and SD of three independent experiments and were measured via unpaired t test. For survival analysis, Kaplan-Meier survival curves were analyzed by a log-rank test. (E) Growth curves of 17D and 17D-IRES in SH-SY5Y cells. Cells were infected with the indicated viruses at an MOI of 0.01. The cell supernatants were collected at the indicated times for determination of the virus titers by plaque assay using BHK-21 cells. Growth curve data represent the means and SD of three independent experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001.