Immune tolerance

A state of unresponsiveness to a specific antigen or group of antigens to which a person is normally responsive.

Immune tolerance is achieved under conditions that suppress the immune reaction and is not just the absence of a immune response.</P> Immune tolerance can result from a number of causes including: > >Prior contact with the same antigen in fetal life or in the newborn period when the immune system is not yet mature; >Prior contact with the antigen in extremely high or low doses; >Exposure to radiation, chemotherapy drugs, or other agents that impair the immune system; >Heritable diseases of the immune system; >Acquired diseases of the immune system such as HIV/AIDS.</LI></UL> Immune tolerance can be defined as a state in which a T cell can no longer respond to antigen.

The T cell 'tolerates' the antigen.