Figure 3: Passive immunization with Cal/09-HA specific antibodies and 2009 H1N1 human-positive sera protects mice from 1918 virus lethality.

(a–c) mice (9 weeks old) were treated with a single dose of either 150 μg of each mAb (150 μl final volume) or 100 μl of human sera intraperitoneally 24 h before challenge with 50 LD₅₀ of 1918 virus, or mock challenged with PBS (mock group). (a) Body weights represent the average from n=5 mice per immunization strategy and error bars represent s.d. of mice remaining at each time point. Statistical significance (*P<0.05) was determined by an unpaired two-tailed Student's t-test for the control mAb group as compared with the mAb treatment groups, and for the human pre-sera as compared with the human post-sera treatment group. (b) Percentage survival of n=5 mice per group. Statistical differences (*P<0.05) are shown as compared as above and were determined by the log-rank test. (c) Lung viral titres of passively immunized mice on days 2 (squares) and 4 (circles) after challenge. Viral titres for n=3 mice per group per time point are shown with their respective average represented as black bars. Significant differences (*P<0.05) in viral titres were determined by an unpaired two-tailed Student's t-test.