T-cell stimulation increases Treg detection by upregulating Foxp3 expression. (A) CD4 T cells were analyzed for Foxp3, CTLA-4, and CD25, Ki67 in a healthy control and a CTLA-4–deficient patient at 0 hours (Hr) and 16 hours after CD3/28 bead stimulation. (B) Percentage of Tregs before or after bead stimulation in controls and individuals with CTLA-4 mutations.