Background and aims The alterations in MHC class I expression play a crucial step in immune evasion of cancer or virus-infected cells. This study aimed to examine whether tolerized grafts modified MHC class I expression.

Methods FVB/N mice were rendered tolerant of C57BL/6 alloantigens by in utero transplantation of C57BL/6 marrows. Postnatally, engrafted donor skins and leukocytes were examined for their MHC expression by quantitative real-time PCR and flow cytometry.

Results In this murine tolerance model established by in utero marrow transplantation, engrafted donor skins up-regulated their MHC class I related gene transcripts after short-term (1~2 weeks) or long-term (>1 month) engraftment. This biological phenomenon was simultaneously associated with up-regulation of TAP1 gene transcripts, suggesting an important role of TAP1 in the regulation of MHC class I pathway. Notably, the surface MHC class I molecules of H-2K^q in engrafted donor leukocytes consistently showed over-expression.

Conclusions Induction of allograft tolerance involved biological modifications of donor transplants. The increased expression of MHC class I within engrafted donor skins of tolerant mice might be used as the tolerance biomarkers for identifying a state of graft tolerance, and paved the way to advancing our insights into the mechanisms of allo-tolerance induction.