Immunohistochemical analysis of clinically transplanted muscles.

BACKGROUND

Although a number of studies have examined the morphology and function of experimentally transplanted muscles, immunohistochemical evaluation of clinically transplanted muscles has not been reported. The purpose of this study was to examine clinically transplanted muscles at long periods after transplantation with biochemical markers specific for satellite cell activation and muscle regeneration.

MATERIALS AND METHODS

Nine biopsies of muscles transplanted to the paralyzed face were examined. In five cases, the gracilis muscles were transplanted about 1 year after cross face nerve grafting. The other four cases underwent one-stage latissimus dorsi (LD) muscle transplantation. Twelve to 162 months after transplantation, muscle biopsies were harvested in nine cases. In eight cases, secondary corrections of facial expression including debulking of the grafted muscle were required, while another muscle was transplanted in one case because of the failed first operation. As control, six specimens of normal LDs were examined as well. Monoclonal antibodies were employed to visualize myosin heavy chain (MHC) isoforms (slow, fast, and embryonic) and MyoD protein.

RESULTS

Although one specimen exhibited only small, atrophic fibers indicating failed reinnervation, the remaining eight specimens showed regularly distributed fibers and type grouping indicating successful reinnervation. There was no statistically significant difference in fiber area and lesser diameter between normal LDs and transplanted LDs. However, even in these successfully reinnervated muscles, intermediate and small fibers expressing embryonic MHC and small cells expressing MyoD were observed, suggesting that satellite cells were activated for repair of the adjacent fibers.

CONCLUSIONS

Muscle adaptation (presumably to denervation), which is a regenerative change accompanied by activation of satellite cells, was still seen even long periods after transplantation. It is concluded that, in microneurovascular human skeletal muscle transfers, there is a wide variation in the time required for reinnervation of individual muscle fibers, and it may be that human muscle fibers cannot be properly reinnervated after denervation has continued for a certain period such as 12 months.