An ultrastructural comparison of peripheral nerve allografts and autografts

Summary There is a marked difference in the cellular response of the host to peripheral nerve allografts and autografts. The response elicited by allografts is characterised by invasion of tissue with lymphocytes, plasma cells and activated macrophages. These cells disrupt the nerve architecture, and cause rupture and consequent compression of the neurolemmal tubes which are the essential conduit element of a nerve graft.By contrast, in the autograft, regeneration follows the initial process of Wallerian degeneration without the complication of immune reaction. The Schwann cells and macrophages rapidly remove the myelin and axons from the neurolemmal tubes of the donor nerve; new axonal sprouts are then able to traverse these channels and reach the periphery in large numbers. If this process is delayed, the neurolemmal tubes in the distal nerve segment are compressed by surrounding collagen which limits the size of regenerating axons.