TISSUE AND ORGAN TRANSPLANTATION
Replacement of diseased or injured organs or tissues by surgery is an important endeavour of modern medical science. Kidney and cornea transplantation and skin grafting are now widely practised. Attempt was made to transplant heart in 1967 which resulted in partial success. Since then attempt to transplant lungs and liver have been made.
Success of transplantation depends upon the genetic compatibilities of donor and recipient’s tissue. Therefore, the first requirement of tissue and organ transplantation is tissue typing. Tissue of the donor must match the tissue of the recipient. Subsequent rejection of transplanted organs or graft is prevented or slowed down by cobalt irradiation or immuno-suppressive drugs to inhibit bodies immune response. There is great disadvantage in such immune suppression. Because this leads to suppress body’s defence system against invasion by pathogens. The high failure rate in transplantation is not due to rejection of organs but because of lack of immunity to invading pathogens.
Future success will depend upon development of drugs which eliminate graft or organ rejecting response. This will leave immune response against disease causing organisms unaltered. It must be remembered that transplantation is not natural as it never occurs in nature. The transplanted organs are rejected because these are foreign to the body like invading microbes. The immune system cannot distinguish between transplanted tissue and pathogen as both are foreign to the body. The fact that immune mechanism is involved in rejection of transplanted organ is more evident by the rejection of second transplant more quickly. This is like immune response in case of subsequent attack by pathogen after immunisation.
Not all individuals of a species possess identical antigens. These antigens segregate genetically within the species. These are called isoantigens. These isoantigens of one individual whose organ is donated produce immune response in the body of the recipient if the latter does not possess these antigen in his body. The genes responsible for the synthesis of isoantigens are referred to as histocompatibility (H) genes. It is therefore necessary to evaluate histocompatibility of tissues before transplantation. If the isoantigens are compatible the transplanted tissues are not rejected. These isoantigens are found to be located in the surface of the cell. Attempts have been made to extract them before transplantation.
Transplantation of donor cornea and skin grafting are most widely practised all over the world with very hight rate of success. Kidney transplantation has also become easier although the success rate is not as high as in the case of skin and cornea transplantation.