Rejection of tissue transplants

The significant participation of certain of these nutritional factors in the production of circulating antibodies to a variety of antigens and the manifestation of delayed hypersensitivity reactions, including the rejection of tissue transplants, have been described. 

General Considerations - The spectrum of potential clinical uses for an effective compound In this area Is continuing to broaden. During the past year a number of reports have appeared which tend to substantiate the role of FA In the hyperacute rejection of tissue transplants. It has been known for some time that antigen-antibody complexes are capable of aggre-... 

Originally developed for chemotherapy, azathioprine is used today mainly as an immunosuppressive agent and rarely as an antineoplastic drug. It was introduced as an immunosuppressive agent by a British pioneer of tissue transplantation, Roy Caine. Azathioprine was used to prevent rejection after tissue transplantation as a replacement for 6-mercaptopurine because it was less toxic. In addition to tissue transplantation, it is also used for rheumatoid arthritis and Crohn s disease. Azathioprine is a prodrug which in the body is converted to its active metabolites 6-mercaptopurine and 6-thioinosinic acid. Until the discovery of cyclosporine, azathioprine in combination with steroids was the standard treatment to prevent rejection after tissue transplantation. 

Fig. 7.1 Phases of tissue transplant rejection. The transplanted tissue sheds antigens. These antigens undergo uptake, processing and presentation to the T cells in the secondary lymphoid tissue by APCs, which include macrophages, B cells, Langerhans cells or dendritic cells. This phase results in the production of antibodies and antigen-specific TH and Tc cells. The antibodies and effector cells then migrate to the grafted tissue where TH cells secrete cytokines and which in combination with the antibodies and Tc cells destroy the grafted tissue (see Color Insert)...

MHC class I and II proteins, the presenters of peptides to T cells, were discovered because of their role in transplantation rejection. A tissue transplanted from one person to another or from one mouse to another is usually rejected by the immune system. In contrast, tissues transplanted from one identical twin to another or between mice of an inbred strain are accepted. Genetic analyses revealed that rejection occurs when tissues are transplanted between individuals having different genes in the major histocompatibility complex, a cluster of more than 75 genes playing key roles in immunity. The 3500-kb span of the MHC is nearly the length of the entire E. coli chromosome. The MHC encodes class I proteins (presenters to cytotoxic T cells) and class II proteins (presenters to helper T cells), as well as class III proteins (components of the complement cascade) and many other proteins that play key roles in immunity. 

MHC class I and II proteins, the presenters of peptides to T cells, were discovered because of their role in transplantation rejection. A tissue transplanted from one person to another or from one mouse to another is usually rejected by the immune system. In contrast, tissues transplanted from one identical twin to another or between mice of an inbred strain are accepted. 

The science of immunology not only encompasses the body s immune responses to bacteria and viruses but is extensively involved in tumour recognition and subsequent rejection the rejection of transplanted organs and tissues the elimination of parasites ftom the body allergies and autoimmunity (the condition when the body mounts a reachon agairrst its own tissues). 

Allograft Tissue or organ transplanted from a donor of the same species but different genetic makeup the recipient s immune system must be suppressed to prevent rejection of the allograft (graft). 

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