CD4 and influenza: 8 days after influenza infection, both GP(1°)PR8(2°) and LCMV(1°)PR8(2°) groups had significantly higher frequencies and numbers of effector tetramer+ CD4+ T cells in medLN than the PR8(1°) and PR8(1°)PR8(2°) groups, with LCMV-primed mice having the highest overall (Fig 2B–2C); while total lymphocytes were mostly comparable across the four groups (S3A Fig).