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Transplant rejection   

Overview | Symptoms | Treatment | Prevention

Alternative names:

Graft rejection; Tissue/organ rejection

Definition:

A consequence of organ or tissue transplantation caused by the transplant recipient's (host's) immune response to the transplanted organ/tissue which can damage or destroy it.  See also graft-versus-host disease.

Causes and Risks

The immune response protects the body from potentially harmful substances (antigens) such as microorganisms, toxins, and cancer cells. The immune system distinguishes "self" from "foreign" by reacting to proteins on the surfaces of cells.  It reacts against substances it recognizes as foreign (antigens). The presence of foreign blood or tissue in the body triggers an immune response that can result in blood transfusion reactions and transplant rejection when antibodies are formed against foreign antigens on the transplanted or tranfused material. Before transplant, tissue is "typed" according to the antigens it contains (Histocompatibility antigens).

No two people (except identical twins) have identical tissue antigens. Therefore, in the absence of immunosuppressive drugs, organ and tissue transplantation would almost always causes an immune response against the foreign tissue (rejection), which would result in destruction of the transplant. Though tissue typing ensures that the organ or tissue is as similar as possible to the tissues of the recipient, unless the donor is an identical twin, no match is perfect and the possibility of organ/tissue rejection remains. Immunosuppressive therapy is used to prevent organ rejection.

There are some exceptions, however. Corneal transplants are rarely rejected because they have no blood supply, so lymphocytes and antibodies do not reach the cornea to cause rejection. And, as mentioned above, identical twins have identical tissue antigens, so transplants from one twin to another are almost never rejected.

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