Mice were inoculated intranasally with the same dose of C. muridarum at 8 weeks after the primary infection when the bacteria have been cleared from their lung tissues (no bacteria had been detectable at 4 weeks after infection and onwards), and the kinetics of the response of NK cells (NK1.1+CD3e−) in the spleen and lung tissues at different time points was measured (Figure 1A). The gene discussed is CD3E; the disease is infection.