P75 nerve growth factor receptor is expressed in regenerating human nerve grafts

Background. The purpose of this study was to elucidate the expression of p75 nerve growth factor receptor (p75NGFR) in human cross-facial nerve grafts and to compare the immunohistological findings with patient data and the functional outcome in facial reanimation. Materials and methods. The study comprised 37 sural nerve graft specimens. All of the patients had long-lasting complete facial paralysis and were operated on by the standard two-stage procedure involving cross-facial nerve grafts and microneurovascular muscle transfer. Nerve biopsies were taken 4 to 20 months (mean, 8 months) after the cross-facial nerve grafting. Immunohistochemistry for p75NGFR as well as for Schwann cells (S-100; Dako, Glostrup, Denmark) and for Neurofilament-200 (NF-200; Boehringer, Mannheim, Germany) was performed. Results. In graft biopsies, the mean number of NF-200-positive axons amounted to 38% (range, 6-81%) of that in control samples. Further, regenerated axons were thinner than in control samples. Morphologically, the grafted nerves were characterized by fibrosis and invasion of inflammatory cells. A longer time between cross-facial nerve grafting and biopsy sampling correlated with a higher number of viable axons (NF-200) (P = 0.002). In all cases, expression of p75NGF receptor was clearly higher at the distal end of the grafted nerve. Expression of p75NGFR was lower in older than in younger patients (P = 0.003). A high expression of p75NGFR was often seen with better function of the transplanted muscle. Conclusion. Increased expression of p75NGFR in human nerve grafts was noted, especially in younger patients. We suggest that p75NGFR expression might be a contributing factor in a successful axonal regeneration and eventual recovery of muscle function. (c) 2008 Elsevier Inc. All rights reserved.