Graft rejection occurs when the immune system attacks foreign tissue with different antigens. Most transplant patients need immunosuppressant medication to prevent rejection. HLA compatibility is important, and identical twins are the best match. Corneal transplants are less likely to be rejected due to lack of blood supply.
A graft rejection is an immune response by the body to destroy foreign cells in the transplanted tissue. Graft rejection occurs because the transplanted tissue or organ has antigens on its cells that do not match the person’s cellular antigens. Only grafts from one identical twin to another are perfect matches, so most transplant patients need to take immunosuppressant medications to keep their body from rejecting the graft.
Grafts are pieces of foreign tissue attached to a patient’s body in some way. The graft can come from another part of the patient’s body, as is the case with skin grafts. The graft can come from a cadaver, as in a heart or liver transplant, or from a living person, as is the case with many kidney and bone marrow transplants.
As mentioned, the best grafts in terms of rejection risk are those from identical twins. Corneal transplants are unusual in that they are rarely refused. This is because the corneas have no blood supply and, therefore, no molecules of the immune system reach the cornea.
Graft rejection occurs because the transplanted tissue has different antigens than the rest of the body. The patient’s immune system is quick to attack foreign materials that display different antigens. Graft donors and recipients are checked for antigen compatibility before performing the transplant to reduce the risk of graft rejection.
The most important of these antigens are the human leukocyte antigens (HLA). These antigens are present on almost every cell in the body, but they get their name because white blood cells carry many of them. There are three main groups of HLA: HLA-A, HLA-B and HLA-DR. Each group contains many different antigens.
HLAs are inherited, so a person will get half of their HLAs from their mother and the other half from their father. Unrelated people tend to have very different HLA profiles, which is why relatives are the first to test for compatibility when a patient needs a transplant. Blood typing must also be done before a graft operation. Some of the O, A, B and AB blood types are incompatible with each other, so a donor patient must have an appropriate blood type and a proper HLA profile.
A transplant is rejected by the immune system if the antigen profiles don’t match and immunosuppressant drugs aren’t doing their job. Immunosuppressive drugs may be needed for the rest of the tissue recipient’s life to prevent graft rejection. Graft rejection is diagnosed if the graft is not working properly or if the patient is ill or experiencing unusual discomfort. Only rarely is a graft rejection manifested by fever, pain, or swelling.
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