These mechanisms are: 1) Tem can survive in the absence of antigen; 2) some Teff may survive to generate Tem, as Teff are capable of re-upregulating CD127 over time, and remain protective; 3) Tcm derived from P. chabaudi-infected animals continue to generate Tem, even after infection is cleared; 4) low-level persistent infection promotes proliferation of Tem. The gene discussed is IL7R; the disease is infection.