Recognition of antigens takes place on specific receptors on T and B cells of the immune system. These encounters may result in either activation or inhibition of lymphocytes, depending on several conditions at the time of encounter. Burnet also proposed that tolerance may occur when fetal immunocytes are exposed to and recognize a specific antigen and that this process leads to deletion of these clones.
Tolerance is mediated through both T and B cells and so lacks both humoral and cellular immunity.
Immature lymphocytes are more susceptible to induction of tolerance than are mature lymphocytes. Tolerance can be induced in mature lymphocytes if they encounter antigens in tissues outside the thymus or bone marrow, under certain conditions. This is called peripheral tolerance. High doses of antigens, orally administered antigens, and repeated low doses of antigens may all lead to tolerance. Antigens with high affinity for their antigen receptors may also induce tolerance rather than activation.