The concept of immune privilege refers to the observation that tissue grafts placed in certain anatomical sites, including the brain and eye, can survive for extended periods of time 1. Immune privilege is thought to reflect an evolutionary adaptation to protect vital structures from damage by inflammatory responses directed against pathogens. It was originally believed that antigens in immune-privileged sites are concealed from the immune system by physical barriers and therefore ignored. However, subsequent studies have shown that antigens do leave immune-privileged sites, that these antigens can induce immune responses, and that immune effector cells can have access to immune-privileged sites. It is now clear that immune privilege is maintained by an active rather than passive process 2,3,4.
The eye is an excellent example of an immune-privileged site. This organ enjoys immune privilege...
