Abstract

Immunological 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. The recognition of antigens by the immature B cells in the bone marrow is critical to the development of immunological tolerance to self. This process produces a population of B cells that do not recognize self-antigens but may recognize antigens derived from pathogens or non self. T cells are selected for survival much more rigorously than B cells. They undergo both positive and negative selection to produce T cells that recognize self-MHC molecules but do not recognize self-peptides. Since, central tolerance is not 100% efficient, mechanisms of peripheral T-cell tolerance are required to prevent autoimmunity. Active peripheral tolerance is maintained by numerous types of regulatory T cells, the best known of which are FoxP3 + Tregs that develop naturally in the thymus or can be induced in the periphery. Central tolerance is the main way the immune system 2 learns to discriminate self from non-self which is clearly stated in the case of early embryo communication within placental barrier. In did so with the natural balance rule the immune tolerance is play an important role on normal physiology to occur.