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.

Natural Tolerance

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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.

Induced Tolerance

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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.