Following 12 h ex vivo stimulation with the LACK158–173 peptide, a distinct LACK158–173+CD4+ T cell population in the spleens of vaccinated mice produced IFN-γ (Fig. 1A), but no IL-4 (data not shown), indicating that LACK158–173 vaccination in the context of influenza induces a Th1-bias. This evidence concerns the gene CD4 and influenza.