Of note, cytokines, such as TNFα and IL-6, all of which are known to be directly correlated with host morbidity and pulmonary injury (Kozak et al., 1997; Hayden et al., 1998; Kaiser et al., 2001), were significantly elevated in bronchoalveolar lavage fluids on day 2 post-infection (Figures 4A,C), implying the importance of immune responses in the disease pathogenesis of our influenza virus infection model. Here, TNF is linked to infection.