CD4 and infection: M2e or NA-specific IgG antibody production in mLN (Fig 6I), IFN-γ secreting cells (Fig 6J), and IFN-γ+CD4+ T cells (Fig 6K) in lungs were observed at higher levels in aged mice with m-cNA-M2e VLP vaccination compared to mock control at day 6 after A/Phil infection.