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. This evidence concerns the gene CD69 and infection.