IRF4 expression reflects TCR signal strength. (A) Isolated blood CD8⁺ T cells were stimulated with increasing concentrations of plate-bound anti-CD3 mAb (0.1-1 μg/mL) for 18 hours. Mean fluorescence intensity of IRF4 in IRF4⁺CD137⁺ cells. A representative result from 3 individual experiments is shown. (B) PBMCs were treated for 30 minutes with increasing concentrations of anti-human pan MHC class I mAb (0-100 μg/mL) and then cultured with CEF peptides for 18 hours. Expression of IRF4, CD69, CD25, and CD137 by activated CD8⁺ T cells was analyzed. A representative result from 6 individual experiments is shown.