Abstract: The normal eye possesses immune privilege. When grafted orthotopically to the eye of experimental animals, allogeneic corneas enjoy a relatively high level of acceptance, compared to orthotopic grafts of other types of solid tissue. Each layer of the cornea displays different potentials of alloimmunogenicity or immune privilege. Immunogenicity of the cornea as an allograft resides within its epithelium and stroma, whereas immune privilege arises from endothelium. Corneal endothelium confers immune privilege on the corneal allografts through constitutive expression of CD95L and B7-H1. These molecules induce apoptosis of effector T cells by binding to CD95 and PD-1 expressed on T cells. These two key molecules play a role on peripheral deletion of allo-reactive effector T cells within corneas to maintain immune privilege of corneal allografts. To reduce allogeneic donor epithelium-derived immunogenicity in transplantation, a reconstituted corneal tissue, eliminating the risk of immune rejection, was created. Replacement of donor epithelium with syngeneneic epithelium protects orthotopic corneal allografts from allo-sensitization and rejection even in high risk recipients.

Key words: corneal transplantation, immune privilege, CD95L, B7-H1, immune rejection