Effect of intrathymic injection of allogene antigen on immune response to sciatic nerve transplantation in allogenic mice

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 μL saline; two weeks later, frozen sciatic nerves of donor mice were transplanted. Immunosuppressive agent group： Mice were given intrathymic injection of 100 μL 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 μL 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.