Transplantation – types of transplant
In the recent years we have become more and more successful in our attempts to remove tissues, even entire organs, from the bodies of persons and cause them to grow in the bodies of others. Transplants, as these operations are called, do not always involve more than one individual, for example, the burned skin of an arm may be replaced with grafted skin taken from the thigh of the same individual. This is known as an autotransplant. An isotransplant in-volves individuals of the same genetic background, such as identical twins. When a transplant is performed between individuals is not genetically related, the transfer of tissue is a homotransplant.
Grafts or transplants attempted between individuals, unless they happen to be identical twins, are usually rejected by the recipient’s body, due to the production of antibodies in the bloodstream. Both drugs and X-rays have been used in attempts to overcome this an¬tibody buildup. So far, any method that suppresses the buildup of antibodies also leaves the patient overly susceptible to infection.
Bone and cartilage, teeth, blood vessels, endocrine gland tissue, kidneys, and even hearts are being grafted or transplanted today with an encouraging degree of success. Often, tissues can be preserved chemically or by freezing until such time as they are needed. Inert (nonreactive) plastics are becoming more and more popular in the replacement of diseased or injured body parts, since they are seldom rejected by the tissues of the recipient. So far, the use of plastics has been somewhat limited to the circulatory system, in arterial grafts and artificial hearts or portions of hearts.
After the first heart transplant in South Africa in 1967 there was a considerable sharp drop in the number of heart transplants. The problem is, whether such operations should be carried out now when the problem of tissue incompatibility has not yet been fully solved. One more important factor, the selection of the donor and the recipient with corresponding groups of tissue proteins also blocks the road to the solution of this problem.
Immunity of an organ safeguards it from alien creatures — microbes, for example. But a transplanted organ or tissue is also alien to the organism, and its antigens reject them just as they reject the microbes. The “mechanism” of rejection is rather simple. The lym¬phocytes — certain type of blood cells — generate antibodies, which move into the place of transplantation and, after a battle, kill the cells of the transplanted organ or tissue.
It turned out, however, that it is possible to establish “peaceful coexistance” of the incompatible tissues within the organism. Groups of tissues exist just as blood groups do. They are distinguished by their antigens, or rather, by the system of antigens. Seventeen anti-gen systems are known today. Surgeons undertake transplants only when the main antigen system of the donor and the recipient coincide. However, even a thorough choice of the donor and the recipient does not guarantee a 100 per cent success of the operation.