Hi.... Peripheral tolerance refers to the tolerance on the functions of the T cell and B cell. T cell and B cell are the immunity cells in the human body. They deliver this funtion by different mechanism. It is activated by the presence of receptors on the cells usually refered to as MHC. The target cells for the MHC is the antigen (anything that is an not part of the body). There are instances when the MHC reacts angainst the own body resulting in the develpment of autoimmunity state or disease. The mechanism where in the develpopment of such autoimnunity is prevented is refered to as development of tolerance. It can happen either at the central level i.e at the stage of the production or at the peripheral level i.e at the stage of its release.