Role of B7-H1 in immune privilege of the eye.

The normal eye possesses immunologic privilege. When grafted orthotopically to the eyes of experimental animals, allogeneic corneas enjoy a relatively high level of acceptance, compared with orthotopic grafts of other types of solid tissue. Even corneas grafted into eyes of preimmunized recipients are often not subject to immune rejection. To understand the molecular mechanisms of immune privilege of the eye, we studied the role of new B7 family co-stimulatory molecules in the maintenance of the immunosuppressive microenvironment of the eye. Programmed death 1 (PD-1) is a new member of the CD28 CTLA-4 family which has been implicated in the maintenance of peripheral tolerance. B7-H1 (PD-L1) and B7-DC (PD-L2), new members of the B7 family, have been identified as ligands for PD-1, but their expression and function in the eye remain largely unknown. The purpose of the present study was to determine whether the PD-1 PD-Ls pathway plays a role in the immune privilege of corneal allografts and, if so, to investigate its mechanism.