Immune Privilege

Certain sites of the human body have immune privilege, meaning they are able to tolerate the introduction of antigens without eliciting an inflammatory immune response. Tissue grafts are normally recognised as foreign antigen by the body and attacked by the immune system. However in immune privileged sites, tissue grafts can survive for extended periods of time without rejection occurring. Immunologically privileged sites were thought to include:

• the brain, but this is now known to be incorrect and indeed immune cells of the CNS contribute to the maintenance of neurogenesis and spatial learning abilities in adulthood
• the eyes
• the placenta and the fetus
• the testicles

Immune privilege is thought to be an evolutionary adaptation to protect vital structures from the potentially damaging effects of an inflammatory immune response. Inflammation in the brain or eye can lead to loss of organ function, while immune responses directed against a fetus can lead to the loss of the fetus.

Medically, a cornea transplant is currently the only procedure that takes advantage of this.