FIG. 1.

Survival profiles of wild-type (wt) and IFN-γ−/− (ko) mice infected with various doses of the WSN virus. Mice were immunized with the live HK (H3N2) virus and challenged 1 month later with the WSN virus (A to C). As controls, we included naive mice and mice immunized with the WSN virus (D). The mice were observed during a period of 20 days following the challenge, and the recovery of survivors was documented by the absence of infectious virus in the lungs. Daily results are expressed as percent survival.