Immunohistochemical assessment of rat nerve isografts and immunosuppressed allografts.

OBJECTIVE: Autologous peripheral nerve grafts are commonly used clinically as a treatment for peripheral nerve injuries. However, in research using an autologous graft is not always feasible due to loss of function, which in many cases is assessed to determine the efficacy of the peripheral nerve graft. In addition, using allografts for research require the use of an immunosuppressant, which creates unwanted side effects and another variable within the experiment that can affect regeneration. The objective of this study was to analyze graft rejection in peripheral nerve grafts and the effects of cyclosporine A (CSA) on axonal regeneration. METHODS: Peripheral nerve grafts in inbred Lewis rats were compared with Sprague-Dawley (SD) rats to assess graft rejection, CSA side effects, immune responses, and regenerative capability. Macrophages and CD8+ cells were labeled to determine graft rejection, and neurofilaments were labeled to determine axonal regeneration. RESULTS: SD rats without CSA had significantly more macrophages and CD8+ cells compared to Lewis autografts, Lewis isografts, and SD allografts treated with CSA. Lewis autografts, Lewis isografts, and SD autografts had significantly more regenerated axons than SD rat allografts. Moreover, allografts in immunosuppressed SD rats had significantly less axons than Lewis rat autograft and isografts. DISCUSSION: Autografts have long been the gold standard for treating major nerve injuries and these data suggest that even though CSA is effective at reducing graft rejection, axon regeneration is still superior in autografts versus immunosuppressed allografts.

Vascularization is delayed in long nerve constructs compared with nerve grafts.

INTRODUCTION: Nerve regeneration across nerve constructs, such as acellular nerve allografts (ANAs), is inferior to nerve auto/isografts especially in the case of long defect lengths. Vascularization may contribute to poor regeneration. The time course of vascular perfusion within long grafts and constructs was tracked to determine vascularization. METHODS: Male Lewis rat sciatic nerves were transected and repaired with 6 cm isografts or ANAs. At variable days following grafting, animals were perfused with Evans Blue albumin, and grafts were evaluated for vascular perfusion by a blinded observer. RESULTS: Vascularization at mid-graft was re-established within 3-4 days in 6 cm isografts, while it was established after 10 days in 6 cm ANAs. CONCLUSIONS: Vascular perfusion is reestablished over a shorter time course in long isografts when compared with long ANAs. The differences in vascularization of long ANAs compared with auto/isografts suggest regenerative outcomes across ANAs could be affected by vascularization rates. Muscle Nerve 54: 319-321, 2016.