Once the infection is eliminated, the CD8 T cell population begins to contract as the bulk of the Listeria-specific CD8 T cells undergo apoptotic cell death; therefore, a skimpy population (5–10%) of Listeria-specific CD8 T cells is left to enter the memory T cell pool, and it is this memory T cell pool that confers better protection upon rechallenge with Listeria monocytogenes [9]. This evidence concerns the gene CD8A and infection.