BACKGROUND: Marrow stromal cells (MSCs) own the characteristic of migration. However, the mechanisms underlying the migration of these cells remain unclear. OBJECTIVE: To explore the roles of stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 in trafficking of MSCs migration. DESIGN, TIME AND SETTING: The in vivo cytology experiment was performed at Department of Anatomy, National University of Singapore from March 2007 to June 2007. MATERIALS: MSCs were isolated and purified from a Wistar neonatal rat. Forty adult female Wistar rats were randomly divided into sham operation and experimental groups, with 20 animals in each group. METHODS: The chemotaxis assay was performed at a 48 well Boyden chamber, and a total of 25 μL SDF-1 was added to the lower layer of chamber, covered with 8 μm polycarbonate membrane filter; SDF-1 cultured in DMEM conditioned medium was served as a blank control group. Cell concentration was regulated to 1.5×109L-1/L. 50 μL and cell suspension was added into the upper layer of chamber, cultured at CO2 incubator with temperature of 37 ℃ for 10 hours. Rats in the experimental group were prepared for transected spinal cord injury models, and in the sham operation'group, only the vertebral plate was opened. 1.0 mL (1×109L-1/L) MSCs suspension labeled with 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) was injected through internal jugular vein at 1 hour after completely transected spinal cord. MAIN OUTCOME MEASURES: Expression of chemokine receptor CXCR4 in MSCs, as well as the effect of SDF-1 on the migration of MSCs was observed by immunofluorescence, change of SDF-1 in lesion site of spinal cord was detected by real-time PCR analysis, as well as the in vivo migration of intravenously injected MSCs was detected by fluorescence microscopy. RESULTS: The pudfied MSCs were positive to CXCR4. Compared to the blank control group, SDF-1 with concentrations of 5, 50, and 500 μg/L could accelerated the migration of MSCs (P < 0.05), which reached a peak with concentration of 500 μg/L. The expression of SDF-1 RNA was obvious increased in the experimental group than that of the sham operation group (P < 0.05), and returned to a normal level at 14 days. At 2 weeks after cell injection, the number of MSCs migrated to the lesion site of completely transected spinal cord was significant increased than sham operation group (P < 0.05). CONCLUSION: SDF-1 may contribute to MSCs migration in vitro and in vivo. SDF-1 and its receptor CXCR4 are involved in the migration of injected MSCs to the lesion site of completely transected spinal cord.Ding P, Xue LP, Yang ZY, Wang CQ, Wang JH, Feng ZT, Ling EA.Chemokine stromal cell-derived factor-1 and its receptor CXCR4 mediate migration of marrow stromal ceils into the lesion site of completely transected spinal cord.