Immune privilege as the result of local tissue barriers and immunosuppressive microenvironments.

As the cellular and molecular bases of immune privilege are elucidated experimentally, the phenomenon emerges as an active and dynamic exercise in immune regulation. Local tissue factors play a key role in the establishment and maintenance of privilege, particularly tissue cytokines and mediators within the local microenvironment, which modify both the induction and expression of immunity to antigens that are introduced into, or arise within, privileged sites.