CD4 and infection: In an M.tb model of infection, fewer M.tb colony‐forming units (CFUs) were observed in the lungs of Rag1‐KO mice that received mito‐transferred naïve CD4+ T cells (p = 0.004) or non‐manipulated naïve CD4+ T cells from old mice (p = 0.01), compared to control infected Rag1‐KO mice (Figure 6D).