We first examined the levels of naive CD8+ T (Figures 4A,E), central memory CD8+ T (Figures 4B,F), effector memory CD8+ T cells (Figures 4C,G), and terminally differentiated effector memory (TEMRA) CD8+ T cells (Figures 4D,H) in mice depleted of CD4+ T-cells, alveolar macrophages, or CD4+ T-cells and alveolar macrophages prior to a secondary infection at 2 and 4 days post-secondary infection. This evidence concerns the gene CD4 and infection.