Cytokine-induced STAT5 phosphorylation in CD8⁺ populations. Representative example of STAT5 phosphorylation induced after stimulation of PBMCs with (A) 1 ng/mL IL-7 or (B) 1 ng/mL IL-15. Results are shown for the HLA-A^*0201-positive patient IM81 studied in the acute disease (IM81.1) and 14 years later (IM81.5), and for an HLA-B^*0801-positive healthy carrier. In each case, STAT5 phosphorylation is analyzed on EBV lytic epitope-specific populations (against the HLA-A^*0201-restricted YVL or HLA-B^*0801-restricted RAK epitope) and EBV latent epitope-specific populations (against the HLA-A^*0201-restricted CLG or HLA-B^*0801-restricted FLR epitopes). Percentage values in the top right quadrant of each dot plot refer to the percentage of STAT5 phosphorylation in tetramer-positive cells, whereas values in the bottom right quadrant indicate the percentage of STAT5 phosphorylation in the total CD8⁺ population. Quadrant boundaries were set using nonstimulated cells from the same donors.