TNF and viral pneumonia: Severe viral pneumonia was observed in the infected mice on Day 4 post-infection, which showed that H1N1 virus infection triggered alveolar tissue destruction (P < 0.01, Figure 1C), pulmonary edema, and hemorrhage (P < 0.01, Figures 1D, E), accompanied by high levels of the inflammatory cytokine TNF-α (P < 0.01, Figure 1F).