CD8A and infection: There were no overt signs of re-infection of mice during the studies, and while we cannot rule out infection at distal sites or responses to endogenous microbes, periodic staining for CD69 demonstrated that Ag-experienced CD8 T cells did not express CD69, a marker of recent activation (Figure S4C in Supplementary Material), suggesting that systemic infection was not occurring and that LM infection is not persistent in outbred mice.