Immune or immunological tolerance is the process by which the immune system does not attack an antigen. It occurs in two forms: innate tolerance and acquired tolerance. The immune system is composed of a complex constellation of cells, organs and tissues, arranged in an elaborate and dynamic communications network and equipped to optimize the response against invasion by pathogenic organisms. ... An antigen is a substance that stimulates an immune response, especially the production of antibodies. ...
Innate tolerance is the body's tolerance for its own antigens and proteins. When naturals tolerance fails, or when the body does not properly recognize itself, an autoimmune disorder results. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ...
Acquired tolerance
Acquired or induced tolerance is the immune system's tolerance for external antigens. It is created through some form of manipulation, such as medication. One of the most important kinds of acquired tolerance occurs during pregnancy where the fetus must be tolerated by the maternal immune system.[1] In clinical practice, acquired immunity is important in organ transplantation, when the body must be forced to accept an organ from another individual. The failure of the body to accept an organ is known as transplant rejection. To prevent rejection, a variety of medicines are used to produce induced tolerance. Oral medication A medication is a licenced drug taken to cure or reduce symptoms of an illness or medical condition. ... An organ transplant is the transplantation of an organ (or part of one) from one body to another, for the purpose of replacing the recipients damaged or failing organ with a working one from the donor. ... Transplant rejection occurs when the immune system of the recipient of an transplant attacks the transplanted organ or tissue. ...
References
^ Trowsdale J, and Betz AG. 2006. Mother's little helpers: mechanisms of maternal-fetal tolerance. Nature Reviews Immunology 7:241-6 PMID 16482172
Tolerance to tissue and cell antigens can be induced by injection of hemopoietic (stem) cells in neonatal or severely immunocompromised (by lethal irradiation or drug treatment) animals.
Tolerance can be broken naturally (as in autoimmune diseases) or artificially (as shown in experimental animals, by x-irradiation, certain drug treatments and by exposure to cross reactive antigens).
Tolerance may be induced to all epitopes or only some epitopes on an antigen and tolerance to a single antigen may exist at the B cell level or T cell level or at both levels.
Immunological tolerance is the failure to mount an immune response to an antigen.
Immunological tolerance is not simply a failure to recognize an antigen; it is an active response to a particular epitope and is just as specific as an immune response.
Both B cells and T cells can be made tolerant, but it is more important to tolerize T cells than B cells because B cells cannot make antibodies to most antigens without the help of T cells.
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