To further investigate the role of FoxO4 in T cell–mediated antipathogen immune responses in vivo, we next applied an infection model using an intracellular bacterial pathogen, Listeria monocytogenes, which is known to induce strong T cell responses by the induction of IFN-γ–producing Th1 cells and CD8+ effector T cells. This evidence concerns the gene FOXO4 and infection.