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 cyt