Origin of Schwann cells in peripheral nerve allografts in the rat after withdrawal of cyclosporine.

The origin of Schwann cells in peripheral nerve allografts following rejection was determined by immunohistochemistry. Sciatic nerve allografts from ACI-RT1a rats were transplanted into Lewis-RT1l sciatic nerves using epineurial sutures. Isografts were taken from Lewis-RT1l rats. Cyclosporine (CsA) was administered subcutaneously daily, 5 mg/kg for 12 weeks, to the rats in each group. Allografts with CsA were sacrificed in groups at 12, 14, 16, 20, 24, and 36 weeks postoperatively during the rejection and recovery phase. Allografts and isografts without CsA were evaluated at 3, 6, 12, and 24 weeks. Nerves were frozen and cross sections immunohistochemically stained against Lewis rat HLA (RT1) and against Schwann cells (S-100 antigen). Allografts without CsA demonstrated minimal reaction to anti-Lewis compared to control isografts, which stained positively at all times. Schwann cells were not as well-stained in the allografts. Allografts with CsA showed reactivity to S-100 at 12 weeks, but minimal activity to Lewis antibody. Minimal reactivity to both S-100 and Lewis existed at 16 weeks, but increased gradually by 24 and 36 weeks. Therefore, Schwann cells from the recipient migrate into the graft and replace the Schwann cells from the donor following rejection.