Role of endothelial cells in allograft rejection.

The immunological properties of endothelial cells suggest they perform a pivotal role in acute and chronic rejection following solid organ transplantation. Their constitutive expression of MHC class II molecules (which initiate allograft rejection by activating CD4 T cells) and accessory molecules allows them to present foreign antigen by both the direct and indirect route to the recipient's immune system. The costimulatory molecules used by endothelial cells appear to differ from those used by traditional antigen-presenting cells such as B cells and dendritic cells. Release of non-HLA antigens from damaged endothelial cells results in a chronic antibody response--possibly contributing to graft vasculopathy and chronic rejection. Further understanding of the factors that regulate MHC class II and accessory molecule expression on endothelial cells could lead to novel strategies of therapeutic intervention.