Migratory behavior of lymphocytes to different concentrations of S1P. Ex vivo chemotaxis assay using unsorted T and B cells from WT or Sphk2 knockout mice treated for 24 hours with FTY720 (A) or for 6 or 24 hours with FTY720-P (B) (1 mg/kg intravenously, each). The percentage of the input cell population that responded to S1P was determined (mean values ± SD, n = 6).