Santosh S. Kale

Effect of cold nerve allograft preservation on antigen presentation and rejection

OBJECT Nerve allotransplantation provides a temporary scaffold for host nerve regeneration and allows for the reconstruction of significant segmental nerve injuries. The need for systemic immunosuppression, however, limits the current clinical utilization of nerve allografts, although this need is reduced by the practice of cold nerve allograft preservation. Activation of T cells in response to alloantigen presentation occurs in the context of donor antigen presenting cells (direct pathway) or host antigen-presenting cells (indirect pathway). The relative role of each pathway in eliciting an alloimmune response and its potential for rejection of the nerve allograft model has not previously been investigated. The objective of this investigation was to study the effect of progressive periods of cold nerve allograft preservation on antigen presentation and the alloimmune response. METHODS The authors used wild type C57Bl/6 (B6), BALB/c, and major histocompatibility Class II-deficient (MHC-/-) C57Bl/6 mice as both nerve allograft recipients and donors. A nonvascularized nerve allograft was used to reconstruct a 1-cm sciatic nerve gap. Progressive cold preservation of donor nerve allografts was used. Quantitative assessment was made after 3 weeks using nerve histomorphometry. RESULTS The donor-recipient combination lacking a functional direct pathway (BALB/c host with MHC-/- graft) rejected nerve allografts as vigorously as wild-type animals. Without an intact indirect pathway (MHC-/- host with BALB/c graft), axonal regeneration was improved (p < 0.052). One week of cold allograft preservation did not improve regeneration to any significant degree in any of the donor-recipient combinations. Four weeks of cold preservation did improve regeneration significantly (p < 0.05) for all combinations compared with wild-type animals without pretreatment. However, only in the presence of an intact indirect pathway (no direct pathway) did 4 weeks of cold preservation improve regeneration significantly compared with 1 week and no preservation in the same donor-recipient combination. CONCLUSIONS The indirect pathway may be the predominant route of antigen presentation in the unmodified host response to the nerve allograft. Prolonged duration of cold nerve allograft preservation is required to significantly attenuate the rejection response. Cold preservation for 4 weeks improves nerve regeneration with a significant effect on indirect allorecognition.

Costimulation blockade inhibits the indirect pathway of allorecognition in nerve allograft rejection.

Nerve allografts provide a temporary scaffold for host nerve regeneration. The need for systemic immunosuppression limits clinical application. Characterization of the immunological mechanisms that induce immune hyporesponsiveness may provide a basis for optimizing immunomodulating regimens. We utilized wild‐type and MHC class II–deficient mice, as both recipients and donors. Host treatment consisted of triple costimulatory blockade. Quantitative assessment was made at 3 weeks using nerve histomorphometry, and muscle testing was performed on a subset of animals at 7 weeks. Nerve allograft rejection occurred as long as either the direct or indirect pathways were functional. Indirect antigen presentation appeared to be more important. Nerve allograft rejection occurs in the absence of a normal direct or indirect immune response but may be more dependent on indirect allorecognition. The indirect pathway is required to induce costimulatory blockade immune hyporesponsiveness. Muscle Nerve, 2011

Utilizing Reverese End-to-Side Neurorrhaphies in Peripheral Nerve Injuries

METHODS: 36 Lewis rats were divided into 3 groups (Figure 1). In Group 1, the right tibial nerve is transected and axonal regeneration from the proximal stump is prohibited. In Group 2, the tibial nerve is transected as described previously. The peroneal nerve is transected distally and coapted to the distal tibial nerve in an end-to-end (ETE) fashion. In Group 3, the tibial nerve is transected as described previously. The peroneal nerve is transected distally and coapted to a perineurial window in the side of the distal tibial nerve in a reverse end-to-side fashion (RETS). In addition, 5 male transgenic Sprague Dawley rats, expressing GFP in neural tissue, underwent the procedure described for Group 3. In these animals, axonal regeneration is visualized over time using confocal microscopy for qualitative assessment. Evaluated outcomes were recorded at two time points (5 and 10 weeks) and included muscle mass, nerve histomorphometry, and nerve stimulation. A one way ANOVA was used to identify differences between individual groups. If significant, a Student Newman-Keuls test was performed for a pairwise multiple comparison.