Table 1.

Conditions that promote immune privilege of corneal allografts

Condition	Mode of action	Effect on immune privilege
Absence of lymph vessels	Prevents APC migration to regional lymph nodes	Prevents induction of immune responses
FasL	Induces apoptosis of activated T cells at the graft–host interface	Blocks expression of immune responses
PD-L1	Inhibits T cell proliferation and induces T cell apoptosis at the graft–host interface	Blocks expression of immune responses
ACAID	Suppresses DTH responses and deviates alloantibody responses to noncomplement-fixing isotypes	Prevents both induction and expression of immune responses
Tregs	Suppress immune responses	Prevent both induction and expression of immune responses

ACAID, anterior chamber-associated immune deviation; DTH, delayed-type hypersensitivity; FasL, Fas ligand (CD95L); PD-L1, programmed death ligand 1; Tregs, T regulatory cells.