Abstract: Objective To observe the effect of transplanted bone marrow mesenchymal stem cells(MSCs) on repairing of the colon tissues of rats with ulcerative colitis. Methods The MSCs from rats were isolated, cultured and labelled with fluor. Forty-five SD Rats were randomly grouped as A, B and C groups. Immune combined TNBS/ethanol was induced in groups A and B. Group C was the control group. The rat in group A received a caudal vein injection of 1ml of a fluids containing the labelled MSCs, and the rat in group B received 1ml of PBS after the induction of colitis. 5 rats in each group were sacrificed at day 3, 7 and 14 after injection. The colonic tissue in 3 groups were collected and prepared as paraffin sections for examination of pathological changes. Some colonic tissues in group A were prepared as frozen sections to observe the distribution of transplanted cells in the colon under a fluorescent microscope, and expression of cytokeratin(CK) of transplanted cells by immunofluorescent staining under a laser confocal microscope. Results The MSCs proliferated rapidly and had a typical fibroblastlike morphology. The repairing of injured colon in group A was much better than that in group B on day 7 and 14. The transplanted cells were seen in colon in group A, and the number of the cells increased as time going and was maximized on day 14(P <0.05). There were a few transplanted cells expressed CK in group A on day 7 and 14. Conclusion The transplanted MSCs distribute in the injured colon of rats with ulcerative colitis, and some MSCs diferentiate into colonic epithelial cells and participate in repair of the i

Key words: Mesenchymalstem cell, Ulcerative colitis, Transplantation, Repair, Immunofluorescence, Rat