P14 memory T cells lacking ThPOK show reduced accumulation upon rechallenge. A, Ninety to 180 days postinfection, CD19+ cell-depleted spleen cells containing 104 ThPOKhd/hd or ThPOKwt/wt P14 cells were transferred into new B6 hosts, and rechallenged with LCMV. The percentages and absolute numbers of each type of P14 T cell 7 days after rechallenge were analyzed for CD8 and Thy1.1 expression. Results are representative of four independent experiments. B, B6 host mice were injected with (open histograms) or without (shaded histograms) 1 mg of BrdU i.p. 6 days after rechallenge. The percentages of BrdU incorporation in ThPOKhd/hd or ThPOKwt/wt P14 cells in PBL were analyzed 6 h after BrdU injection. Results are representative of two independent experiments. C, Bcl-2 expression levels (open histograms) in ThPOKhd/hd and ThPOKwt/wt P14 cells from the spleen before (90–180 days postinfection) or 7 days after the secondary challenge. Shaded histograms are isotype controls. The numbers in the histograms indicate MFI of Bcl-2.