REJECTION AND REGENERATION THROUGH PERIPHERAL-NERVE ALLOGRAFTS - IMMUNOPEROXIDASE STUDIES WITH LAMININ, S100 PROTEIN AND NEUROFILAMENT ANTISERA

The pattern and temporal sequence of histopathological events in a rat nerve allograft model were evaluated. Following grafting and varying survival periods (from 1 to 30 weeks), the host and donor nerve were r emoved and assessed by light and electron microscopy. Nerve allografts underwent Wallerian degeneration and rejection. Wallerian degeneratio n was the dominant pathologic process at weeks 1 and 2 after engraftme nt. Histologic rejection started as an epineurial process at weeks 1 a nd 2, became progressively endoneurial and was most prominent at 4 and 6 weeks after engraftment. Rejection was accompanied by evidence of g raft Schwann cell and endoneurial tube loss. The rejection process del ayed, but did not prevent, nerve regeneration by the host. Regeneratio n of fine neurofilament-positive axonal sprouts into the proximal port ions of the graft was observed as early as week 2. Subsequently, regen eration occurred through the periphery and around the exterior of the rejected nerve allograft fascicle. Regenerating axons were accompanied by S100 protein reactive Schwann cells and newly synthesized laminin- positive endoneurial tubes. Regenerating axons reinnervated the distal host segment at week 8 and increased in number and myelination therea fter. The observations of rejection and regeneration through nerve all ograft segments are discussed in reference to previous studies.