FIG. 4.
VRP pretreatment dramatically reduces the viral load in the serum and brain of animals challenged with VEE. Adult BALB/c mice (3 mice per group) were pretreated by inoculation in the RRFP with 2 × 106 null VRP for 6, 12, or 24 h prior to challenge with 10 PFU of virulent VEE in the opposing LRFP. Mock-pretreated mice received diluent 6 h prior to challenge. 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. 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.