Transplant rejection

Transplant rejection is a common complication of an organ transplant. Although medical science has advanced greatly since the first organ transplants, rejection is still a common possibility even in a well matched donor.
The immune system naturally attacks any tissue it identifies as not being genetically identical to the host body. However, the severity of the reaction is mitigated and aggravated by several factors, the most important of which is how close the antigens on the transplanted tissue match those of the host. For example, in blood transfusions, where three antigens (A, B, and Rhesus factor) are at issue, as long as none of the antigens in the donor blood are not also present in the host, the body will not trigger an immune reaction.
However, there are several other factors that play into rejection. The age of the patient is important as adults have a more well developed immune system that is more likely to reject a transplant. Also important are any damage to the transplant tissue, which can trigger an inflammatory response that can cascade.
Rejection is generally classified in three categories:
*Hyperacute, where the transplanted organ triggers a massive inflammatory response that is almost always fatal.
*Acute, where the host suffers severe but reversible symptoms of rejection.
*Chronic, where the organ slowly deteriorates. This is generally asymptomatic from an immune standpoint, but will show gradual failure of the transplanted organ. This is a near inevitability for most transplanted organs. 
Transplant patients are routinely given drugs that suppress the immune response, such as prednisone or other steroids, and other immunosuppressants.
Also see: Graft-versus-host disease
Transplant rejection at Wikipedia
Category:Immunology