In contrast to findings with CD8+ cells, the frequencies of influenza-specific CD4+ cells were not reduced in aged or FoxN1 K14KO mice (Figure 3C), consistent with findings that cytolytic T-cell activity and perforin expression by CD4+ cells are normal in the elderly after influenza vaccination, whereas these functions are impaired in CD8+ cells [22]. The gene discussed is PRF1; the disease is influenza.