Certain sites of the mammalian body have<unk> , meaning they are able to tolerate the introduction of antigens without eliciting an inflammatory<unk>  response. Tissue grafts are normally recognised as foreign antigen by the body and attacked by the<unk>  system. However, in<unk> d sites, tissue grafts can survive for extended periods of time without rejection occurring.<unk> logically<unk> d sites include: * the eyes * the placenta and fetus * the testicles * the central nervous system<unk>  is also believed to occur to some extent or able to be induced in articular cartilage. This was once thought to also include the brain, but this is now known to be incorrect, as it has been shown that<unk>  cells of the central nervous system contribute to the maintenance of neurogenesis and spatial learning abilities in adulthood.<unk>  is thought to be an evolutionary adaptation to protect vital structures from the potentially damaging effects of an inflammatory<unk>  response. Inflammation in the brain or eye can lead to loss of organ function, while<unk>  responses directed against a fetus can lead to miscarriage. Medically, a cornea transplant takes advantage of this, as does knee meniscal transplantation.
Immune privilege
Antineoplastic resistance
Extravasation 
Tumor initiation
Immune tolerance
Clonal hematopoiesis
Tumor budding
Tissue expansion