Role of OX40 in the genesis and suppressor functions of CD4⁺Foxp3⁺ Tregs. (A). Real-time RT-PCR analysis of Foxp3 gene transcripts in CD4⁺CD25⁺ Tregs sorted from wt C57BL/6 and OX40KO mice. Data shown are representative of 3 individual experiments. (B) Spleen (SP) and lymph node (LN) cells from wt foxp3gfpKI mice and OX40KO foxp3gfpKI mice were stained with cychrome–anti-CD4 and then compared for the presence of CD4⁺GFP(Foxp3)⁺ T cells by FACS. The data shown are representative data of 4 individual experiments. Numbers in quadrants are the relative percentage of cells in each region given by the flow cytometer. (C) CD4⁺GFP⁻ T effector cells sorted from foxp3gfpKI mice were mixed with CD4⁺GFP(Foxp3)⁺ Tregs from wt and OX40KO foxp3gfpKI mice at different ratios, and suppression of T effector cell proliferation was shown. The data shown are representative of 4 individual experiments. Error bars represent SD of triplicate assays.