Immune tolerance or
immunological tolerance describes a state of unresponsiveness of the immune system to substances or tissue that have the capacity to elicit an immune response. It contrasts with conventional immune-mediated elimination of foreign
antigens (see
Immune response). Tolerance is classified into
central tolerance or
peripheral tolerance depending on where the state is originally induced—in the
thymus and
bone marrow (central) or in other tissues and
lymph nodes (peripheral). The mechanisms by which these forms of tolerance are established are distinct, but the resulting effect is similar.