To this end, C57BL/6 mice were vaccinated intranasally with S-FLU(H1N1) or intranasally infected with influenza virus (PR8), and on days 28 to 30 after infection, the capacity of NP-specific CD8+ T cells in the spleen and lung tissue to synthesize interferon-γ (IFN-γ) and tumor necrosis factor–α (TNF-α) after a brief in vitro stimulation with NP peptide were measured (Fig. 2A). This evidence concerns the gene CD8A and infection.