Design and characterization of a model of murine skin graft rejection: Visualizing the immune response against a defined minor transplantation antigen

The underlying cellular interactions causing rejection of minor histocompatibility antigen (mHAg) mismatched allografts are not well understood. To gain a more complete and comprehensive understanding of these processes, a murine model of transplantation was designed where a single, defined minor antigenic disparity exists between donor and recipient. Transgenic C57BL/6 (B6) mice were generated expressing a membrane-bound form of the chicken ovalbumin (OVA) protein. Splenocytes from the Act-mOVA-I transgenic line failed to produce a primary mixed leukocyte reaction (MLR) when cultured with B6 T lymphocytes in vitro, but could stimulate TCR-transgenic CD4+ and CD8+ T cells responsive to peptides from OVA, consistent with the expected response against a mHAg. Transplantation of skin grafts from Act-mOVA-I donors onto wild-type B6 recipients resulted in rejection by a month post-transplant, in a T cell-dependent, B cell-independent manner. In addition, both CD4 + and CD8+ T cells were required for normal rejection.; The adoptive transfer of the OVA-specific CD4+ and CD8 + TCR-transgenic T cells into recipient mice one day prior to grafting resulted in accelerated rejection and allowed the antigen-specific T cell response to the foreign mHAg to be monitored in vivo. Tracking of the transferred cells via congenic surface markers revealed activation localized to the graft-draining nodes, expansion beginning around day 4 after grafting, peaking between days 9 and 11 Then declining dramatically by the time the rejection was complete. Quantitative immunohistochemical analysis of the grafted skin showed a pronounced accumulation of the transferred population, particularly the transgenic CD8+ T cells, in the Act-mOVA-I graft itself without appearance in control B6 isografts. Additionally, the presence of the antigen-specific CD4+ T cells enhanced the expansion of the transgenic CD8+ T cells, thereby providing even more cytotoxic cells in the graft parenchyma. Analysis of the graft tissue also revealed increased expression of the peptide:major histocompatibility complex (MHC) target recognized by the CD8+ T cells during the rejection process, indicating that the tissue contributed to its own destruction.; These results demonstrate that rejection of a single mHAg-expressing skin graft occurs in coordinated fashion with direct analogy to the natural immune response to a foreign pathogen.