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We investigated the origin of the epithelium in transplanted cryopreserved tracheal allografts in rats and tried to clarify the mechanism by which immunogenicity is reduced in this procedure.Tracheal transplantation was performed with PVG rats (allele at the RT1 locus: c) used as donors and ACI rats (allele at the RT1 locus: a) as recipients. After resection of a 5-ring segment of the cervical trachea of an ACI rat, the trachea was reconstructed with the cryopreserved tracheal segment of a PVG rat (n = 6). No immunosuppressive agents or steroids were given. Histologic changes were determined and immunohistochemical staining was performed to investigate major histocompatibility complex class I antigens of the transplanted tracheal segment.Two months after tracheal transplantation, 6 surviving ACI rats were killed. Histologically, the epithelium and tracheal cartilage of the transplanted cryopreserved segment displayed normal structure. Immunohistochemical staining showed that the major histocompatibility complex class I antigen of the ACI rat was expressed in the epithelium of the transplanted segment and that the class I antigen of the PVG rat was expressed in the cartilage of the transplanted segment.After transplantation of the cryopreserved trachea, the epithelium of the transplanted cryopreserved segment originated from the recipient epithelium whereas the cartilage retained the structure of the donor trachea. We hypothesize that transplantation of a cryopreserved trachea leads to the growth of the recipient's epithelium over the donor trachea, thereby reducing the antigenicity of the transplant.