Expression of Foxp3 mRNA in tissues of different strains of mice. (A) Relative expression of Foxp3 mRNA by real-time PCR. RNA was extracted from homogenized suspensions of thymus, spleen, or lymph nodes. Symbols represent the fold increase or decrease expression in individual mice, and the bar indicates the mean. (B) To verify that detection of Foxp3 by real-time PCR was selective for Treg cells, thymocytes from C57BL/6 mice were sorted for Treg cell markers. Expression was highest in the CD4⁺CD25⁺ subset that includes Treg cells. (C) Expression of Foxp3 mRNA by real-time PCR in sorted CD4⁺CD25⁻ or CD4⁺CD25⁺ cells from spleens of C57BL/6, IL-7^−/−, IL-7Rα^−/−, TSLPR^+/+, and TSLPR^−/− mice. Cells for each strain were pooled from at least 2 mice. (D) Quantification of Treg cells (CD4⁺CD25⁺ and CD4⁺Foxp3⁺) in spleen of IL-7Rα^−/− mice was compared with C57BL/6, IL-7^−/−, or TSLPR^−/−. Cells were gated on CD3. Representative individual mice from groups of at least 4 mice are shown.