Fig 4. Viral titers in tissues and brain cytokine levels in IFNAR^-/- mice infected with wild-type or chimeric viruses.

(A) Virus titers in tissues after s.c. infections with 1 × 10⁴ PFU of MR766, PRVABC59, MR/PR(C), MR/PR(prM) or MR/PR(E) (n = 5–10 mice per group). Organs were harvested at 6 dpi, and viral titers were determined by CCID₅₀ assays. Limit of detection was 0.83 log₁₀CCID₅₀/g indicated by the horizontal dashed line. Kolmogorov-Smirnov test or t-test were used for statistical analyses. (B) Inverse correlation between percent survival and mean virus titer in the brain and spinal cord. Significance was determined by Spearman’s correlation test. (C) Virus titers in tissues after i.c. infections with 1 × 10⁴ PFU of MR766, PRVABC59, MR/PR(C), MR/PR(prM) or MR/PR(E) (n = 5–12 mice per group). Organs were harvested at 4 dpi, and viral titers were determined by CCID₅₀ assays. Limit of detection was 0.83 log₁₀CCID₅₀/g indicated by the horizontal dashed line. Statistical analysis was performed by t-test. (D) Survival of 10–11-week-old IFNAR^-/- mice infected with 1 × 10⁴ PFU of MR766 (n = 12), PRVABC59 (n = 12), each chimeric virus (n = 6) or uninfected (n = 4). Comparisons of Kaplan-Meier survival curves between different groups were performed by log-rank analysis. (E) mRNA levels of TNFα, IL-1β and IL-6 in brains at 6 days after s.c. infections (n = 6 mice per group). Three uninfected mice were used as controls. Cytokine mRNA levels in brains were normalized to RPL13 mRNA levels. Statistical analysis was performed by t-test. (F) As in (E) at 4 days after i.c. infection.