Table 2.

Central and peripheral immunologic tolerance.

	Central Tolerance	Peripheral Tolerance
Features	Inactivation of cells required for initiation of an immune response.	Inhibition of expression to the immune response.
Site of tolerance induction	Generative lymphoid organs.	Peripheral lymphoid tissues.
Site of involvement	Afferent limb of the immune response, which is concerned with sensitization and cell proliferation.	Afferent limb of immune response, which is concerned with the generation of effector cells.
B cell participation	Immature B cells.	Mature B cells.
T cell participation	Immature thymocytes.	Mature T cells.
Mechanisms of tolerance	Clonal deletion (apoptotic cell death, negative selection).	Clonal deletion (apoptotic cell death); clonal anergy (functional inactivation without cell death); clonal ignorance (failure to recognize or recognition of antigens without costimulation); suppression of lymphocyte activation and effector functions by regulatory lymphocytes.
Function	Eliminates potentially self-reactive lymphocytes.	Maintains unresponsiveness to self-antigens.