Immune Privileged Sites, Such as the Brain, the Eye, and the Testis

Immune privileged sites, such as the brain, the eye, and the testis, are often the targets of autoimmune attack. Thus, once effector T cells are generated that have specificity for autoantigens expressed in these tissues, the effector cells can gain entry to the tissue and cause tissue damage. However, under normal circumstances, the priming and differentiation of effector cells specific for antigens found in the brain, for example, is generally prevented. This is because 'immune privileged' sites:

A) Express antigens that never leave the tissue where they are produced
B) Are surrounded by tissue barriers that block all lymphocyte trafficking
C) Express the cell death receptor, Fas
D) Express the cytokine, TGF- $\beta$
E) Promote the differentiation of T_H17 cells