BACKGROUND: The majority of studies addressing spinal cord ischemia/reperfusion injury (SCIRI) have focused on drugs, proteins, cytokines, and various surgical techniques. A recent study reports that human umbilical cord mesenchymal stem cell (hUCMSC) transplantation achieves good therapeutic effects, but the mechanisms underlying nerve protection remain poorly understood.OBJECTIVE: To observe survival of transplanted hUCMSCs in SCIRI rat models and the influence on motor function in the hind limbs, to determine interleukin-8 expression and cellular apoptosis in spinal cord tissues, and to verify the hypothesis that hUCMSC transplantation exhibits protective effects on SCIRI.DESIGN, TIME AND SETTING: A randomized, controlled, animal experiment was performed at the Laboratory of the Department of Orthopedics in the First Affiliated Hospital of Soochow University,China between January 2007 and December 2008.MATERIALS: hUCMSCs were harvested from umbilical cord blood of healthy pregnant women after parturition in the Obstetrical Department of the First Affiliated Hospital of Soochow University, China. Rabbit anti-human BrdU monoclonal antibody was provided by DAKO, USA. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) Kit and enzyme-linked immunosorbent assay (ELISA) Kit were purchased by Wuhan Boster, China. METHODS: A total of 72 healthy, Wistar, adult rats were randomly assigned to three groups: sham-surgery, model, and transplantation, with 24 rats in each group. SCIRI was induced in the model and transplantation groups via the abdominal aorta block method. The inf rarenal abdominal aorta was not blocked in the sham-surgery group. Prior to abdominal aorta occlusion, 0.2-0.3 mL bromodeoxyuridine (BrdU)-labeled hUCMSCs suspension (cell concentration 5 × 10~3/μL) was injected through the great saphenous vein of the hind limb, and an equal volume of physiological saline was administered to the model and sham-surgery groups.MAIN OUTCOME MEASURES: Pathological observation of rat spinal cord tissues was performed by hematoxylin-eosin staining at 6, 24, and 48 hours post-surgery. Immunohistochemistry was applied to determine hUCMSCs survival in the spinal cord. The amount of cellular apoptosis and interleukin-8 expression in spinal cord tissues was assayed utilizing the TUNEL and ELISA methods, respectively. Motor function in the hind limbs was evaluated according to Jacob's score. RESULTS: Numerous BrdU-positive cells were observed in spinal cord tissues from the transplantation group. The number of apoptotic cells and interleukin-8 levels significantly decreased in the transplantation group (P < 0.05), pathological injury was significantly ameliorated, and motor function scores significantly increased (P < 0.05) compared with the model group. CONCLUSION: Via vein transplantation, hUCMSCs were shown to reach and survive in the injury area. Results suggested that the transplanted hUCMSCs contributed to significantly improved pathological changes in the injured spinal cord, as well as motor function, following SCIRI. The protective mechanism correlated with inhibition of cellular apoptosis and reduced production of inflammatory mediators.