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Immunological tolerance is the process by which the immune system does not attack an antigen. It occurs in two forms: natural tolerance and induced tolerance. This article or section contains information that has not been verified and thus might not be reliable. ... The immune system is the system of specialized cells and organs that protect an organism from outside biological influences. ... An antigen is a substance that stimulates an immune response, especially the production of antibodies. ...
Natural Tolerance
Natural 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. ...
Induced Tolerance
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 roles of induced tolerance is in organ transplantation, when the body must be forced to accept an external organ. 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. ...
This is the first example of the phenomenon we came to call immunologicaltolerance; the red cells could not have "adapted" themselves to their strange environment, because they were in fact identified as native or foreign by those very antigenie properties which, had an adaptation occurred, must necessarily have been transformed.
Tolerance is not an all-or-nothing phenomenon: every degree of tolerance is to be found, from that which allows a graft to live just perceptibly longer than would be expected of it in a normal animal to that in which the graft is permanently accepted by and incorporated into its host.
Tolerance unaccompanied by any symptom of runt disease is produced by the injection of embryonic cells or by a natural or artificial parabiosis between embryos, and it leads here to a stable chimerism in which native and foreign cells seem to coexist without the one ousting the other.
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