This change in the early dynamics of infection in aged mice, with fewer bacteria present during the first 24 h, correlates with decreased and/or bimodal upregulation of costimulatory molecules by the CD8α+ DC population in aged animals at early time points post-infection (Fig. 4A–C), and with decreased CD8 T-cell priming and accumulation (Figs. 1 and 2). This evidence concerns the gene CD8A and infection.