Immune Privilege - Mechanisms

Mechanisms

Antigens from immune privileged regions have been found to interact with T cells in an unusual way inducing tolerance as opposed to a destructive response. Immune privilege has emerged as an active rather than a passive process.

Physical structures surrounding privileged sites cause a lack of lymphatic drainage, limiting the immune system's ability to enter the site. Other factors that contribute to the maintenance of immune privilege include:

• low expression of classical MHC class Ia molecules
• expression of immunoregulatory nonclassical, low polymorphic class Ib MHC molecules
• increased expression of surface molecules that inhibit complement activation
• local production of immunosuppressive cytokines such as TGF-β
• presence of neuropeptides
• constitutive expression of Fas ligand that controls the entry of Fas-expressing lymphoid cells.

The nature of isolation of immunologically privileged sites from the rest of the body's immune system can cause them to become targets of autoimmune diseases or conditions, including sympathetic ophthalmia in the eye.