BACKGROUND: The latest researches demonstrate that intrathymic injection of MHC antigen which reaches a certain dosage (2 mg, i.e., 4 × 108 cell extraction) can induce immunologic tolerance under non-antilymphocyte serum condition.OBJECTIVE: To investigate the effect of intrathymic injection of allogene antigen on survival and function of sciatic nerve in allogenic mice.DESIGN: Randomized controlled animal study.SETTING: The 4th Affiliated Hosptial of Harbin Medical University.MATERIALS: A total of 32 male donor C57BL/6(H-2b) mice of 4 - 8 weeks old and weighing 18 - 22 g and 44 female receptor Balb/c(H-2d) mice of 4 - 8 weeks old and weighing 18 - 22 g were selected from Heilongjing Veterinary Institution. The animal experiment had got confirmed consent from local ethic committee.METHODS: The experiment was carried out in the Laboratory (Provincial Key Laboratory) of the Fourth Hospital, Harbin Medical University from June 2006 to May 2007. C57BL/6(H-2b) mice were anesthetized to extract MHC (H-2b) antigen from splenic cells and sciatic nerves. Allogenous nerve transplantation group:Mice were given intrathymic injection of 100 μ L saline; two weeks later, frozen sciatic nerves of donor mice were transplanted. Immunosuppressive agent group: Mice were given intrathymic injection of 100 μ L saline; two weeks later, fresh sciatic nerves of donor mice were transplanted. At three days before transplantation, 10 mg/kg per day cyclosporin A was intraperitoneally injected once a day till mice were sacrificed. MHC (H-2b) antigen injection group: Mice were given intrathymic injection of MHC (H-2b)antigen from C57BL/6(H-2b) donor mice; two weeks later, fresh sciatic nerves of donor mice were transplanted. Autogenous nerve transplantation group: Mice were given intrathymic injection of 100 μ L saline; two weeks later, fresh sciatic nerves were transplanted.MAIN OUTCOME MEASURES: ① Three weeks later, transplanted part of exposured sciatic nerve was used to measure the motor nerve conduction velocity. ② Transplanted nerve was stained with histochemical staining and observed light microscope and electron microscope. ③ Mice received mixed lymphocyte culture and delayed-typed hypersensitiveness to observe absorbency and measure depth of soles.RESULTS: All 76 mice were involved in the final analysis. ① Motor nerve conduction velocity: The nerve recovery in MHC (H-2b) antigen injection group was higher than that in allogenous nerve transplantation group, equal to immunosuppressive agent group and lower than autogenous nerve transplantation group.There were significant differences among them (P ＜ 0.05). ② Histological changes of transplanted nerve:Light and electron microscopes demonstrated that there were a lot of regenerative nerve fibers in autogenous nerve transplantation group, immunosuppressive agent group and MHC (H-2b) antigen injection group, and all nerve fibers passed grafts. ③ Immunological examination: There was no significant difference in mixed lymphocyte culture among allogenous nerve transplantation group, autogenous nerve transplantation group and MHC (H-2b) antigen injection group (P ＜ 0.05). Depth of soles in other groups was deeper than that in the MHC (H-2b) antigen injection group, and there was significant difference (P ＜ 0.05); that was to say,delayed-typed hypersensitiveness was remarkable.CONCLUSION: The intrathymic injection of allogene MHC antigen may induce specific immune tolerance to allogenous sciatic nerve transplantation and promote nerve survival and functional recovery.