During acute viral infections in mice, IL‐7Rα and KLRG1 together are used to distinguish the short‐lived effector cells (SLEC; IL‐7RαloKLRGhi) from the precursors of persisting memory cells (MPEC; IL‐7RαhiKLRG1lo). The gene discussed is KLRG1; the disease is viral infectious disease.