IFN-γ protects mice from lethal EHV-1 RacL11 challenge. (A and B) Average body weights (A) and percentages of survival (B) of CBA mice treated with different dosages of IFN-γ. CBA mice (n = 8) were treated intranasally with 1, 2.5, 3.5, or 5 μg of murine IFN-γ per mouse (Cell Sciences, Canton, MA) and were challenged with RacL11 (1.5 × 106 PFU/mouse) at 3 h posttreatment. (C and D) Average body weights (C) and percentages of survival (D) of CBA mice treated with IFN-γ. Mice (n = 8) were treated with 3.5 μg of murine IFN-γ 24 h prior to, 3 h prior to, 3 h following, or 24 h following EHV-1 RacL11 (1.5 × 106 PFU/mouse) infection. Mice immunized with KyA (2 × 106 PFU/mouse) were challenged with RacL11 (1.5 × 106 PFU/mouse) at 3 dpi. (E) Virus titers from the lungs of CBA mice treated with IFN-γ. Mice (n = 6) were treated with 3.5 μg/mouse of murine IFN-γ and were challenged with RacL11 (1.5 × 106 PFU/mouse) at 3 hpi. Mice immunized with KyA (2 × 106 PFU/mouse) were challenged with RacL11 (1.5 × 106 PFU/mouse) at 3 dpi. On days 2 to 4 postchallenge, virus titers in the lungs were determined as described in the legend to Fig. 4. Triple asterisks indicate statistical significance (P < 0.01).