Treatment of mice with FTY720 induces T-cell sticking in PP HEVs. (A) Splenocytes and PLN cells from T-GFP mice were injected intravenously into WT mice (n = 6 mice/group), which had been pretreated 2.5 hours earlier with FTY720 or saline. After 30 minutes, PPs were harvested and single-cell suspensions were analyzed by FACS for the presence of GFP⁺ T cells. Homed T cells were increased in PPs of FTY720-treated mice by 62%; *P < .05. (B-C) The intravascular behavior of calcein-labeled WT and S1P₁^–/– T cells in PP HEVs of untreated or FTY720-treated recipients was analyzed by IVM (n = 4 mice/group). (B) WT T-cell rolling and sticking fractions (9.4% ± 2.2% in control mice versus 14.4% ± 2.0% in FTY720-treated mice; P = .05) and (C) S1P₁^–/– T-cell rolling and sticking fractions (11.5% ± 2.8% in control mice versus 26.0% ± 5.0% in FTY720-treated mice. Error bars indicate SEM. *P < .05).