Persistent antigen presentation is required to maintain memory CD8⁺ T-cell inactivation. CD45.1⁺ OT-I effector/memory cells were transferred i.v. to 11c.OVA or nontransgenic (non-tg) mice. (A) At 3, 7, and 28 days after transfer, the total number of splenic DC (CD11c^hi) in 11c.OVA (▴) and non-tg (■) recipients or untransferred 11c.OVA (▵) and non-tg (□) controls was determined. *11C.OVA + effector/memory OT-I is significantly reduced (P < .05) relative to 11c.OVA no transfer. (B,C) CD8⁺ cells were isolated from 11c.OVA mice 42 days after transfer and retransferred to 11c.OVA or non-tg secondary recipients. After 21 days, secondary recipients were challenged with OVA/QuilA or left unchallenged, and 7 days later, spleens were collected (B) and the total number of OT-I (CD45.1⁺/CD8^+/Vα2⁺) T cells (C) and IFN-γ production by OT-I (CD45.1⁺/CD8⁺) T cells determined. Data (A,B) are pooled (mean±SD, or individual values) from 2 independent experiments with 2 mice per group (C) or representative of 2 individual mice for each group in each of 2 independent experiments. Horizontal bars in panel B represent mean values. Numbers on graphs in panel C are percentages of cells in each gate.