Transplant rejection is when a transplant recipient's immune system attacks a transplanted organ or tissue. See also graft-versus-host disease.

Your body's immune system protects you from potentially harmful substances, such as microorganisms, toxins, and cancer cells. These harmful substances have proteins called antigens on their surfaces. If your immune system identifies antigens that are foreign (not part of your body), it will attack them.

In the same way, foreign blood or tissue can trigger a blood transfusion reaction or transplant rejection. To help prevent this, tissue is "typed" before the transplant procedure to identify the antigens it contains.

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.

• The organ does not function properly
• General discomfort, uneasiness, or ill feeling
• Pain or swelling in the location of the organ (rare)
• Fever (rare)

The doctor will feel the area over and around the transplanted organ, which may feel tender to you (particularly with transplanted kidneys).

There are often signs that the organ isn't functioning properly. For example:

• Less urine output with kidney transplants
• Yellow skin color and easy bleeding with liver transplants
• Shortness of breath and less tolerance to exertion with heart transplants

A biopsy of the transplanted organ can confirm that it is being rejected. A routine biopsy is often performed to detect rejection early, before symptoms develop.

When organ rejection is suspected, one or more of the following tests may be performed prior to organ biopsy:

• Lab tests of kidney or liver function
• Kidney ultrasound
• Kidney arteriography
• Abdominal CT scan
• Heart echocardiography
• Chest x-ray