Host responses after acellular muscle basal lamina allografting used as a matrix for tissue engineered nerve grafts

Background. A nerve gap must be bridged by autologous nerve grafts that serve as scaffold and consist of viable Schwann cells that promote regeneration. Owing to the necessary immunosuppression, nerve allografts remain limited to special cases. Alternatively, tissue engineering of peripheral nerves focuses on the implantation of cultured Schwann cells into suitable scaffolds. We established grafts from Schwann cells and basal lamina from acellular muscles. These grafts offer a regeneration that is comparable to autologous nerve grafts. Methods. Using a rat model (DALEW.1W strain), the present study evaluates the host response to acellular muscle allografts by assessing cellular reaction major histocompatability (MHC) class I and II, lymphocytes, macrophages. The results were compared to untreated muscle allografts. Results. Macroscopically, the untreated muscles showed a strong inflammatory reaction as a sign of rejection, whereas the acellular muscle offered only minor reactions in the periphery of the graft. Expression of MHC I and II and invasion of CD4/CD8 positive cells and macrophages was pronounced after grafting the untreated muscles. Only a moderate reaction was noted for these parameters after acellular grafting. Conclusions. The acellular muscle graft is not completely free of cellular response; however the reaction is considered to be moderate and is located only in the periphery. To date, synthetic scaffolds that represent endoneurial tube-like structures and allow sufficient adhesion of Schwann cells and axonal regeneration are not available. The decreased response to acellular muscle allografts offers at least a basis for further experiments.