FIG. 5.

VRP pretreatment dose is a critical parameter in mediating protection against VEE challenge. Adult BALB/c mice (5 mice per group) were pretreated with decreasing doses of null VRP (2 × 10⁶ IU, 10⁵ IU, or 10⁴ IU) inoculated in the RRFP for 6 h prior to challenge with 10 PFU of virulent VEE (LRFP). Mock-pretreated mice received diluent 6 h prior to challenge. (A) Animals were monitored daily for morbidity and mortality. (B) At 24 h postchallenge, serum was collected by tail vein bleed. At 88 h postchallenge, mice were euthanized and then perfused with PBS, and the brain (including the olfactory bulbs) was resected. At each dose of VRP pretreatment, subsequent challenge virus titers were determined by standard plaque assay on BHK cells. Bars represent mean values ± the standard error of the mean. The assay limit of detection (LOD) is indicated by the dotted line.