Similar to 8 days after influenza challenge, heterologously primed mice maintained significantly higher frequencies and numbers of I-Ab:gp66-77 tetramer+ CD4+ T cells in medLN 42 days after influenza challenge compared to the unprimed PR8(1°) and homologously primed PR8(1°)PR8(2°) groups (Figs 4A and S5A). This evidence concerns the gene CD4 and influenza.