Figure 2. S1P₁ blocks thymic differentiation of T_reg cells.

(a) Flow cytometry of total and gated CD4SP thymocytes isolated from WT control, S1P₁-KO and S1P₁-Tg FTOC. Panels on the right show the proportions and absolute numbers of Foxp3⁺ CD4SP T_reg cells with the mean (+s.d.) calculated from ≥8 mice of each genotype. (b) Flow cytometry of gated CD4SP thymocytes from WT control, S1P₁-KO and S1P₁-Tg mice. Panels on the right show the proportions and absolute numbers of the CD4⁺CD25⁺Foxp3⁻ precursor population, with the mean (+s.d.) calculated from ≥8 mice of each genotype. (c) Induction of Foxp3 expression in the CD4⁺CD25⁺Foxp3⁻ population in vitro. CD4⁺CD25⁺Foxp3⁻ cells were purified and stimulated with medium alone, IL-2 or IL-15 for 20 h, and induction of Foxp3 expression was measured by flow cytometry. The lower panel shows an IL-2 dependent dose response curve. Data are representative of 5 independent experiments. *, P < 0.05; **, P < 0.01 (Student’s t-test).