S1P induces degranulation of human LAD2 mast cells and cytokine release. LAD2 cells 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 for 2 hours with increasing concentrations of Ag (10, 30, 100 ng/mL, ) or with 30 ng/mL Ag, as indicated. Degranulation was assessed by β-hexosaminidase release (A). Secretion of TNFα (B) and IL-6 (C) was measured by ELISA. Data are the means plus or minus SD of triplicate determinations. Similar results were obtained in 3 independent experiments. *P < .01.