EBV-specific IFNγ-producing CD8⁺ T cells in PBMCs of EBV-seropositive (A through D) and EBV-seronegative (E and F) individuals. PBMCs were stimulated with autologous LCLs (B, D, and F) 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. Unstimulated PBMCs were also incubated, fixed, and then mixed with autologous LCLs before staining (A, C, and E). The frequency of CD8⁺/CD69^high T cells that produced IFNγ is shown as a percentage of the total number of CD8 cells.