This is performed because greater antigen difference causes more rapid and severe rejection. A few exceptions occur. Corneal transplants are rarely rejected because they have no blood supply, so lymphocytes and antibodies do not reach the cornea to cause rejection. Identical twins have identical tissue antigens, so transplantation between identical twins almost never causes rejection. Suppression of the immune system is usually necessary for the rest of the transplant recipient's life to prevent rejection.
Symptoms vary with the specific organ or tissue.
Signs of reduced organ function are often present. A biopsy of transplanted organs confirms rejection. Routine biopsy is often performed to detect rejection early, before symptoms develop. An X-ray , CT scan, or other procedure may indicate inflammation, swelling, or reduced organ function. Suppression of the immune response is used for both treatment and prevention of transplant rejection.