Effect of cold nerve allograft preservation on antigen presentation and rejection

Abstract

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.

Fig. 1

Direct and indirect pathways of alloantigen presentation by donor and host (recipient) antigen-presenting cells, respectively, for T-cell activation.

Fig. 2

Photomicrographs of histological specimens of nerve graft or distal to nerve graft showing excellent regeneration in the untreated isograft group (A), poor regeneration in the allograft group (B), and improved regeneration with 4 weeks of cold allograft preservation (C). Toluidine blue. Original magnification × 400.

Fig. 3

Graph showing the total number of myelinated fibers in the isograft and allograft control groups and in knockout mice without cold preservation (CP). Superior regeneration was observed in the isografts and improved regeneration in the absence of the indirect pathway (MHC−/− with BALB/c allograft).

Fig. 4

Graph showing the total number of myelinated fibers after 1 week of cold allograft preservation with no significant difference between groups or improvement compared with no cold preservation.

Fig. 5

Graph showing the total number of myelinated fibers after 4 weeks of cold allograft preservation with all groups demonstrating significantly improved regeneration.

Fig. 6

Graph showing that when only the indirect pathway was intact, the total number of myelinated fibers was significantly improved after 4 weeks compared with 1 week or no cold preservation.

Fig. 7

Graph showing that when only the direct pathway was intact, improvement in nerve regeneration after 4 weeks was not statistically different compared with regeneration after 1 week or no cold preservation.