Flow cytometric analysis of IFNγ production in 2 CD8⁺ EBV-specific CTL lines from donor KK (A and B) and YI (C and D). (A and C) Unstimulated CTLs; (B and D) CTLs stimulated with autologous LCLs at a responder stimulator ratio of 1. After fixation and permeabilization, the cells were stained for CD8, CD69, and IFNγ. CD8⁺ cells were gated and analyzed by flow cytometry. The frequency of CD8⁺/CD69^high T cells that produced IFNγ is shown as a percentage of the total number of CD8 cells.