MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

BIOLOGY

SECTION 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.3. Biology of Individual Development

Transplantation and The Immune System

It can be considered that the surgical phase of Organ and tissue transplantation has been successfully resolved. Technically, surgeons are capable of transplanting any organ or tissue. However, in all cases except autotransplantation, graft rejection occurs due to tissue incompatibility between the donor and the recipient. Graft rejection is driven by immune responses developed in reaction to its Antigens. Therefore, the causes of rejection are genetic, while the mechanisms of rejection are immune-mediated. The graft rejection reaction involves the generation of T-effectors (T-killers) that release cytotoxic substances. This constitutes transplantation Immunity, which destroys the "foreign" tissue.

Nevertheless, in certain instances, the Organism may perceive foreign antigens as its own and fail to produce Antibodies against them. This phenomenon is termed immunological tolerance. Immunological tolerance was discovered in 1953 in various subjects independently by two scientists: Czech embryologist M. Hašek and English zoologist P. Medawar. Their experiments demonstrated that if foreign Proteins (antigens) are introduced into an organism during the Embryonic Stage of development, adult animals will subsequently perceive them as their own. The organism will exhibit tolerance toward them. These studies confirmed F. Burnet's hypothesis (1949) that the establishment of immunological Homeostasis occurs during the early period of organismal development during the formation and development of lymphoid tissue. Such animals can receive transplants without the risk of rejection. Furthermore, the induction of polyvalent tolerance to all tissue antigens of a given species is also possible. To achieve this, a mixture of antigens from A large number of animals must be administered simultaneously. The polyvalent tolerance method demonstrates the feasibility of overcoming immunological incompatibility, thereby opening up new Perspectives for medicine.

Ways to overcome tissue incompatibility:

1. Matching donor and recipient via the HLA system. Structure/149.html">The problem of donor and recipient Selection is extremely complex. To address it, special international organizations have been established to process information regarding the immunological, hematological, and clinical status of individuals awaiting transplantation. Banks of donor Organs, Tissues, and Cells have also been established.

2. Suppression of immunity (immunosuppression) through: a) irradiation; b) administration of antimetabolites that inhibit nucleic acid synthesis (such as Imuran) or block Protein Synthesis (glucocorticoids); c) use of antilymphocyte serum; d) use of heparin to improve microcirculation.

The most crucial task of modern immunology is not to suppress immunity globally, but specifically to suppress transplantation immunity while preserving the body's protective function against infectious agents.