Rejection and regeneration in peripheral nerve homografts in rats after withdrawal of cyclosporin: morphological and immunohistochemical assessment.

Peripheral nerve homografts 35 mm long were inserted in rats to study rejection and regeneration of nerves after suspension of an immunosuppressant (cyclosporin), and the correlation between the Schwann cells of the host and the donor during the course of regeneration. Sciatic nerve homografts from 36 ACI-RT1a rats were transplanted into Lewis-RT1(1) rats. Isografts were taken from 24 Lewis rats. Cyclosporin 5 mg/kg/day was given subcutaneously for 12 weeks. In the homograft group the myelinated axons that regenerated while the immunosuppressant was being given were covered mainly with Schwann cells from the donor, and after the immunosuppressant was withdrawn both Schwann cells of the donor and axons were rejected. However, while the cyclosporin was being given the Schwann cells of the host migrated into the nerve graft together with a few myelinated axons that escaped rejection, and unmyelinated axons that regenerated after rejection were myelinated by the Schwann cells of host.