S1P but not FTY720 induces degranulation of human mast cells. (A) LAD2 mast cells were treated with vehicle, S1P (100 nM), phospho-FTY720 (100 nM), or ionomycin (1 μM) for 2 hours or sensitized overnight without anti–DNP IgE (1 μg/mL), washed, and then treated with Ag (1, 10, 100 ng/mL) for 2 hours. (B) LAD2 cells were sensitized overnight with anti–DNP IgE, washed, and treated with FTY720 (1 μM) for 2 hours before stimulation with Ag (10 ng/mL) or FTY720 (1 μM) for 15 minutes. Degranulation was determined by hexosaminidase release. Data are means ± SD of quadruplicate determinations. Similar results were obtained in 5 independent experiments.