The role of vascular endothelium in cardiac allograft rejection

This thesis examines whether mouse non-hematopoietic cells such as vascular endothelium have the capacity to activate alloreactive T lymphocytes and trigger acute allograft rejection via direct allorecognition. To test in vitro responses of T cells to endothelial cells, I have established a method to culture mouse vascular endothelium from thoracic aorta. In addition, a multi-parameter flow cytometric method was established to evaluate bi-directional interactions between endothelial cells and T lymphocytes. This allows for the possibility to assess T lymphocyte-mediated apoptosis of endothelial cells in vitro, a process likely contributing to acute and chronic allograft rejection. Studies dissecting effector pathways of cytotoxic T lymphocytes show that CTL-mediated apoptosis of endothelial cells is predominantly due to the perforin/granzyme exocytosis pathway. While, consistent with their expression of histocompatibility and costimulatory molecules, mouse vascular endothelial cells are able to activate and regulate the survival of unprimed alloreactive CD8+ T lymphocytes, they are unable to induce the proliferation of allogeneic CD4+ T lymphocytes. Finally, this thesis describes that, while non-hematopoietic components of allografts do not contribute to CD4+ direct allorecognition, vascularized cardiac allografts can be rejected via CD8+ direct allorecognition when the MHC class I mismatch is presented only by nonhematopoietic cells such as vascular endothelium. This observation, which is the first demonstration of the in vivo capacity of non-hematopoietic cells to initiate allograft rejection, could have important implications for the development of tolerance induction protocols