Transplant rejection is when a transplant recipient's immune system attacks a transplanted organ or tissue. See also
Graft rejection; Tissue/organ rejection
Causes, incidence, and risk factors
In the same way, foreign blood or tissue can trigger a
Though tissue typing ensures that the organ or tissue is as similar as possible to the tissues of the recipient, the match is usually not perfect. No two people (except identical twins) have identical tissue antigens.
Immunosuppressive drugs are needed to prevent organ rejection. Otherwise, organ and tissue transplantation would almost always cause an immune response and result in destruction of the foreign tissue.
There are some exceptions, however. Corneal transplants are rarely rejected because corneas have no blood supply -- immune cells and antibodies do not reach the cornea to cause rejection. In addition, transplants from one identical twin to another are almost never rejected.