<p><b>OBJECTIVE</b>To determine the role of sphingosine 1-phosphate receptor (S1PRs ) signaling in CD34+ hematopoietic stem/progenitor cell transmigration.</p><p><b>METHODS</b>CD34(+) cells were separated by Ficoll density gradient centrifugation and incubated in DMEM medium with 10% fetal calf serum. The cells were pretreated by FTY720, with or without pertussis toxin (PTX) and antiCXCR4 mAb in the medium, followed by addition of 100 ng/ml SDF-1 into the lower chamber of a Costar 24-well transwell. The migrated cells were counted using FACS and the migrating rates were determined. The expressions of sphingosine 1-phosphate receptors were analyzed in CD34(+) cells before and after the transmigration by reverse transcriptase- polymerase chain reaction (RT-PCR). Cord blood CD34(+) cells were treated with or without FTY720 (10(+) mol/L), and the expressions of CD49d (VLA-4), CD11a (LFA-1), and CD62L (L-selectin) were analyzed at 1, 8, and 16 h after the treatment.</p><p><b>RESULTS</b>While FTY720 did not affect spontaneous migration, a substantial increase of SDF-1-induced transmigration was observed in the presence of FTY720 (15.26 2.14 to 28.64 2.37). The FTY720-enhanced transmigration was completely blocked by addition of PTX or antiCXCR4 mAb. S1p1-5 was expressed in fresh isolated cord blood CD34(+) cells. The migrating cells stimulated by FTY720 and SDF-1 only expressed S1P1, S1P3, and S1P4. The expressions of CD49d, CD11a and CD62L on CD34(+) cells treated with FTY720 remained unchanged at the selected time points as compared with the control.</p><p><b>CONCLUSIONS</b>S1PRs are involved the transmigration of CD34(+) cells. The activation of S1PRs results in increased chemotactic response of CD34(+) to SDF-1. These effects are mediated through CXCR4 and PTX-sensitive Gi proteins. Only the CD34(+) cells expressing the specific receptors can rapidly transmigrate. The activation of the S1PRs does not affect the expressions of the adhesion molecules on cord blood CD34(+) cells.</p>