Certain sites of the mammalian body have immune privilege (no immunity), meaning they are able to tolerate the introduction of antigens without eliciting an inflammatory immune response. Tissuegrafts are normally recognised as foreign antigens 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.[1] Immunologically privileged sites include:
Immune privilege is also believed to occur to some extent or able to be induced in articular cartilage.[2][3][4] This was once thought to also include the brain, but this is now known to be incorrect, as it has been shown that immune cells of the central nervous system contribute to the maintenance of neurogenesis and spatial learning abilities in adulthood.[5]
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 miscarriage.[6]
^Ziv Y, Ron N, Butovsky O, Landa G, Sudai E, Greenberg N, Cohen H, Kipnis J, Schwartz M (February 2006). "Immune cells contribute to the maintenance of neurogenesis and spatial learning abilities in adulthood". Nat Neurosci. 9 (2): 268–75. doi:10.1038/nn1629. PMID16415867.
^Garrett JC, Steensen RN, Stevensen RN (1991). "Meniscal transplantation in the human knee: a preliminary report". Arthroscopy: The Journal of Arthroscopic and Related Surgery. 7 (1): 57–62. doi:10.1016/0749-8063(91)90079-D. PMID2009121.