An immunologically privileged site
is any of those locations in the body--the brain
, anterior chamber
of the eye, testis
, renal tubule
, and possibly joints and adrenal glands
--where immune response to antigens
are not destructive to tissue or is suppressed. It is necessary due to unique self-proteins that reside only in particular tissues and do not travel through the lymphatic system
. Examples of tissue-specific proteins include myelin
of the central nervous system
. Such proteins are sequestered in organs and extracellular fluid does not travel the lymphatic system, meaning they do not come into contact with T cells during negative selection
in the thymus
to these sites are not rejected.
Immune response is modified by the privileged sites through anti-inflammatory cytokine release of TGF-beta, which suppresses immune responses likely to cause tissue damage (favors B-cell antibody release vs. macrophage activation). Cells express FasL on their surface, which binds to cytotoxic T cells and causes the cytotoxic T cells to apoptose rather than destroy the tissue of privileged sites.
Medically, a cornea transplant is currently the only procedure that takes advantage of this.