Measurement of mRNAs. mRNA was measured for Foxp3 (A), GITR (B), CCR8 (C), TNFR2 (D), CTLA-4 (E), and TGF-β1 (F) in purified CD4⁺CD25⁺ versus CD4⁺CD25^- or CD8⁺CD25⁺ versus CD8⁺CD25^-thymocytes. mRNA was obtained from CD4⁺CD25⁺, CD4⁺CD25^-, CD8⁺CD25⁺, or CD8⁺CD25^-thymocytes purified by MACS. Columns represent mean values (± SD) of mRNA levels obtained in 4 separate experiments by using real-time quantitative RT-PCR. ^*P < .01.