To study the involvement of different T cell subsets in the initial response against influenza, we characterized by flow cytometry the changes in cell populations on the basis of their expression of different surface markers: γδ T cells (CD3+/B220–/γδ TCR+), CD8+ T cells (CD3+/B220–/γδ TCR–/CD8α+/CD4–), CD4+ T cells (CD3+/B220–/γδ TCR–/CD8α–/CD4+), NK1.1+ double negative (DN) T cells (CD3+/B220–/γδ TCR–/CD8α–/CD4–/NK1.1+), and NK1.1– DN T cells (CD3+/ B220–/γδ TCR–/CD8α–/CD4–/NK1.1–; Fig. 1A). This evidence concerns the gene CD8A and influenza.