Immune tolerance

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.

Innate tolerance (also known as oral tolerance)
Innate tolerance is the body's tolerance for its own antigens and proteins, such as food taken into the body by mouth. When natural tolerance fails, or when the body does not properly recognize itself, an autoimmune disorder results.

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 natural kinds of acquired tolerance occurs during pregnancy where the fetus must be tolerated by the maternal immune system. One model for the induction of tolerance during the very early stages of pregnancy is the eutherian fetoembryonic defense system (eu-FEDS) hypothesis. . However, another model suggests that the induction of tolerance primarily requires the participation of regulatory T cells. 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.