Suggested mechanism of tolerance includes (a) clonal deletion, (b) clonal anergy, and (c) suppression.
i. Clonal deletion: Clones of B and T lymphocytes thatrecognize self-antigens are selectively deleted in embryonic life, hence are not available to respond on subsequent exposure to antigen. This is known as clonal deletion.
ii. Clonal anergy: Clonal anergy means a condition in whichclones of B and T lymphocytes that recognize self-antigens might be present but cannot be activated.
iii. Suppression: In this mechanism, clones of B and T lym-phocytes expressing receptors that recognize self-antigens arepreserved. However, expression of immune responses following antigen recognition might be inhibited by active suppression.