Immune system self-tolerance

One fundamental property of an animal s immune system is that it does not normally react against its own body constituents, i.e. it exhibits tolerance. However, clinical and experimental evidence shows that certain diseases exist in which the patient apparently destroys his/her own cells. The reactions could involve Tc cells, B cells orNK cells, and the result of the reaction with antigen may result in a pathological condition arising (autoimmune disease). Autoimmunity is the mirror-image of tolerance and reflects the loss of tolerance to self... 

Tolerance is the process that allows organ-specific antigens to be accepted as self.2,6 This would mean that the immune system would cease to respond to the allograft, and immunosuppressive medications would not be necessary. Immune tolerance has not been accomplished successfully in humans.2,6... 

Autoimmune diseases in which immunological self-tolerance breaks down and the immune system launches an attack on self-antigens. 

In addition to having an overabundance of several self-antigens, tumor cells express unique antigens, which can be recognized by the host immune system, provided that the immune system is simultaneously activated. Without this activation, the immune system will become tolerized to the unique antigens known as tumor-associated antigens (TAAs), which are usually small peptides of 8 to 10 amino acids. The potential exists for the eradication of cancers by injection of TAAs and the subsequent immune response. Indeed, there have been many tumor-reactive CTLs identified that recognize specific TAAs (15). 

V6. Van Rarijs, L., and Abbas, A. K., Homeostasis and self-tolerance in the immune system Turning lymphocytes off. Science 280, 243-248 (1998). 

Tolerance Prevents the Immune System from Attacking Self-Antigens... 

Tolerance prevents the immune system from attacking self-antigens. To understand tolerance we must appreciate how T cells work. T cells recognize a combination of self and nonself. The cell surface antigens rec-... 

In fetal life, if an immature antibody-producing cell displays cell-surface antibody that binds a normal body component, then the cell dies. Thus, usually, in the adult animal, no cells exist that can make antibodies against the animal s own macromolecules. This inability to make antibodies against self is called self-tolerance. However, in some disease states (the so-called autoimmune diseases) the immune system loses its tolerance against self-antigens. 

Regulatory T-cells (sometimes known as suppressor T-cells) are a specialised subpopulation of T-cells that act to suppress activation of the immune system and thereby maintain immune-system homeostasis and tolerance to self-antigens. 

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