BACKGROUND: Nerve allograft rejection is an unavoidable problem for nerve allografts. Traumatic peripheral nerve injuries are commonly reconstructed using autogenous nerve grafts. However, this form of reconstruction is limited by insufficient autologous nerves for large gap repairs and by morbidity at the nerve donor site.OBJECTIVE: To examine sciatic nerve regeneration and immune tolerance reaction after intragastric administration of ultraviolet B-irradiated (UVB) donor splenocytes.DESIGN, TIME AND SETTING: A complete randomized grouping design and controlled experiment. The experiments were conducted in the Department of Orthopedics, the First Affiliated Hospital to Shanxi Medical University, China, between March and October 2007.MATERIALS: Fourteen adult male SD rats and fourteen male Wistar rats, weighing 250-300g, were randomly matched as donors and acceptors. A further seven male SD rats (weight 250-300g, age 12-16 weeks) were used for nerve isografts. Immune preparations and the Epics XL flow cytometer were purchased from B-D Company, USA. A computer-assisted electromyograph machine was provided by Keypoint P, Dantel Company, Denmark.METHODS: Splenocytes from Wistar rats were isolated, purified, and cultured, and then irradiated with ultraviolet B. In the first control group (Group 1), the SD rats received a syngeneic SD nerve isograft. In the second control group (Group 2), the SD rats received a nerve allograft from Wistar rats without pretreatment. In the oral-tolerance treated group (Group 3), the SD recipient rats were inoculated with 2.5×107 Lewis UVB-irradiated donor splenocyte cells by intestinal tract administration at seven days before transplantation.MAIN OUTCOME MEASURES: (1) The recent end and the middle and distal end of the transplanted nerve were cut at 8 and 12 weeks after operation. Recovery of nerve regeneration was measured with HE staining using the total number, density, and diameter of the nerve fibers. (2) The level of CD25+T lymphocytes in peripheral blood was detected with the Epics XL flow cytometer at one week after operation. (3) The bilateral sciatic nerves were exposed from the sciatic notch up to 0.5mm beyond the distal graft site at eight weeks post-engraftment. Bipolar platinum stimulating electrodes were placed under the sciatic nerve proximally and the mean conduction velocity was recorded with recording electrodes on the posterior tibial nerve at 0.3cm distal to the nerve graft.RESULTS: Eight weeks after operation, total axon number and fiber density in Group 3 were higher than that in Group 1 (P