IL2 and infection: Interestingly, the frequency of CD8+ T cells producing IFNγ, IL-2, or TNFα after stimulation with HA-specific peptides was significantly higher in H1N1-infected mice on day 35 post-infection (Fig. 2), although the absolute number of HA+ Pent+ CD8+ T cells was higher after immunization than after infection at this time point (Fig. 1B).