The S1P–S1P₁ axis remains active in Il4ra^−/− mice. (A) Quantitative PCR of CD62L⁺HSA⁻ SP4 T-conv from WT and Il4ra^−/− mice. mRNA levels were normalized to β-actin; error bars indicate SEM, and data are typical of three independent experiments. (B) Thymic sections from Il4ra^−/− mice stained for CD31, ERTR7, and CD8. C, cortex; M, medulla; *, PVS. Data represent three experiments, n = 4. Bars, 100 μm. (C) Flow cytometry of thymocytes from WT and Il4ra^−/− mice i.v. injected with anti-CD4PE (top). Quantitation of anti-CD4PE–labeled SP4 cells in WT and Il4ra^−/− mice (bottom); n = 6 from two separate experiments. Surface levels of S1P₁ (D) and CD69 (E) in conventional SP4 thymocytes from WT and Il4ra^−/− mice. (D) Gray histogram is peripheral blood CD4⁺ T cells; data represent at least three experiments, n = 6. (E) Gray histogram is CD69 on total SP4 thymocytes, Data represent at least three experiments, n = 10 for WT and Il4ra^−/− mice. (F) Effects of FTY720 in WT and Il4ra^−/− mice. (Top) CD4/CD8 in total thymocytes. (Bottom) CD62L/HSA in conventional SP4 thymocytes. (G) Proportions of total SP4 and CD62L⁺HSA⁺ SP4 T-conv. Data represent at least two experiments, n = 8. Error bars indicate SEM. A Mann-Whitney nonparametric U test was performed. *, P < 0.05; **, P < 0.01; ***, P < 0.001.