Persisting SLP-76–deficient H-2D^b:GP33⁺ CD8⁺ T cells from cKO mice are unable to respond to TCR signals. Forty-eight weeks after SLP-76 deletion, mice were rechallenged with LCMV clone 13 infection, and expansion was assessed quantitatively in peripheral blood at days 3 and 5 after infection. Data are gated on: (A) total CD8⁺, (B) CD8⁺CD44^hi, and (C) CD8⁺H-2D^b:GP33⁺ cells. Cells are further gated for YFP expression, with the YFP⁺ populations shown in the left column and YFP⁻ populations shown in the right column. Each data point shows mean and standard deviation from 2 mice in each cohort. (D) Splenocytes from cHET and cKO mice were isolated at day 5 after rechallenge and stimulated in vitro for 4 hours. Samples were stained for immunophenotyping and intracellular cytokine expression. Histograms are gated on YFP⁺CD8⁺CD44^hi cells. Numbers in the top right quadrant show the relative percentage of cells in each gate. Shaded histograms represent cHET mice; black line histograms represent cKO mice. Data are representative of stimulations from 2 cHET and 2 cKO mice.