By 24 hrs post infection when bystander IFN-γ production by memory CD8 T cells was highest in mice that received 5 × 106 CFU Att LM and 1 × 106 CFU Vir LM infection (Fig. 5b), serum IL-12 levels were significantly greater in mice that received either of these two infections compared to mice that received 1 × 104 or 1 × 105 CFU Vir LM infection (Fig. 5c). This evidence concerns the gene IFNG and infection.