Expression of IRF4 by activated human blood CD8⁺T cells. Healthy donor PBMCs were stimulated with 1 μg/mL SEB and analyzed for the expression of surface and intracellular molecules at the indicated time points by flow cytometry. (A) IRF4 and CD69 expression by CD8⁺ T cells after stimulation with SEB. (B) IRF4 and CD69 expression by CD8⁺ T cells in unstimulated PBMCs (left panel) and PBMCs stimulated with SEB for 18 hours (right panel). (C) IRF4 and CD69 expression (left panel) and CD25 and CD137 expression (right panel) by CD8⁺ T cells after 18 hours of SEB stimulation. (D) Frequency of IRF4⁺CD69⁺, CD137⁺, and CD25⁺CD137⁺ cells in CD8⁺ T cells from healthy donor PBMCs after 18 hours of SEB stimulation (n = 24). Each point represents an individual donor. (E) IRF4 and CD69 expression in CD8⁺ T_CM cells (CD45RA⁻CCR7⁺), T_EM cells (CD45RA⁻CCR7⁻), naive T cells (CD45RA⁺CCR7⁻), and T_EMRA cells (CD45RA⁺CCR7⁺) in SEB-stimulated PBMCs. (F) Mean fluorescence intensity (MFI) of IRF4 of baseline CD8⁺ T_CM, T_EM, naive T, and T_EMRA cells (left panel) and after 18 hours of SEB stimulation (right panel) in healthy donor PBMCs (n = 3). Horizontal lines indicate the mean (± standard deviation). Each symbol represents an individual donor. *P < .05, **P < .01, **** P < .0001, 1-way analysis of variance with Tukey’s test. NS, not significant.