CD4 T cell memory does not restore the ability of infused LLO91-99–specific CD8 CTLs to expand or to confer protective immunity 7 days after transfer. (a) We transferred 6 × 106 LLO91-99–specific CTLs into recipient mice and infected the mice with wild-type L. monocytogenes 7 days later. Thirty minutes prior to infection, 50 × 106 splenocytes from a BALB/c mouse immunized more than 28 days earlier with LLOSer92L. monocytogenes were infused into the CTL recipients. Seventy-two hours after infection, spleens and livers were cultured; bacterial counts are plotted on the y axis. (b) We transferred 6 × 106 LLO91-99–specific CTLs into recipient mice that had been infected with LLOSer92L. monocytogenes more than 28 days earlier. Seven days after CTL infusion, recipients were infected with wild-type L. monocytogenes, and 72 hours later, splenocytes were stained for CD8α and Thy1.1 and with LLO91-99 H2-Kd tetramers. Dot plots are gated on live CD8 T cells. Staining for Thy1.1 is shown on the y axis, and tetramer staining is shown on the x axis. Numbers in the upper right quadrants represent percentages of total CD8 T cells. Data are representative of two animals per group.