Demonstration of specific antigenic peptide TCR-triggered CD25 upregulation on cytochromec peptide TCR transgenic mouse T lymphocytes. B10A TCR-transgenic mouse splenocytes were incubated at 5 × 10⁶ cells/mL with 1 μmol/L of cytochrome c peptide for 2, 4, 6, and 8 hours. The cells were then labeled with (1) FITC antimouse CD25, (2) PE antimouse TCRαβ, and (3) PI. CD25 expression on the TCR⁺ cells was evaluated by flow cytometry by gating for PI⁻ (live) and PE-antimouse TCRαβ⁺ cells. (A) Flow cytometry profiles of CD25-expressing TCRαβ⁺ cells. The shaded histograms show changes in CD25 expression after 2 (graph a), 4 (graph b), 6 (graph c), and 8 (graph d) hours of stimulation. The solid histogram (control) in graph a represents the CD25 level on T cells from a sample that was not incubated with antigenic peptide. (B) Time-dependent changes in percentages of CD25⁺ cells among TCRαβ⁺ cells was calculated from data in (A).