SphK1 is important for degranulation of hMCs and CCL2 and TNF-α secretion. Purified cord blood–derived mast cells (hMCs) were transfected with control siRNA (□) or SphK1 siRNA (■). (A) SphK1 mRNA levels normalized to GAPDH mRNA were measured by QPCR. (B-D) hMCs were sensitized overnight with IgE and then treated with 30 ng/mL Ag or ionomycin (1 μM) for 2 hours. Degranulation (B) and secretion of CCL2 (C) and TNF-α (D) were determined. Data are the means plus or minus SD of triplicate determinations. Similar results were obtained in 3 independent experiments. *P ≤ .01, #P ≤ .05.