Effect of S1P on hMC functions. Purified cord blood–derived mast cells (hMCs) were treated with vehicle, increasing concentrations of S1P (1 nM, 10 nM, 100 nM, 1 μM), or ionomycin (1 μM) for 2 hours, or sensitized overnight with anti-DNP IgE (1 μg/mL) washed, and then stimulated with increasing concentrations of Ag (10, 30, 100 ng/mL) for 2 hours. Degranulation was assessed by β-hexosaminidase release (A), and secretion of CCL2 was measured by ELISA (B). Data are the means plus or minus SD of triplicate determinations from a single experiment. Similar results were obtained using cells from 2 different donors. (C) Migration of IgE-sensitized hMCs toward increasing concentrations of S1P (1, 10 μM), Ag (30 ng/mL), or FN (20 μg/mL) was determined in transwell chambers.