Transplantation barriers
Given the extent of the natural polymorphism in a population,
the donor and the recipient will always differ for allelic variants of
numerous proteins (except for monozygote twins). Such differences will
represent transplantation barriers when recognized by the immune system.
Different types of alloantigenic structures
- Blood groups
Blood groups represent important transplantation barriers when blood is transfused because incompatible ABO blood group antigens of the donor are recognized by the recipient’s natural antibodies. Blood group antigens are also expressed on vascular endothelial
cells of the organs. Hence, matching of blood groups is essential in organ
transplantation (even if no blood is transfused!) because the recipient's
natural antibodies may recognize the antigens on the graft and cause its
rejection.Read more...
- Major histocompatibility antigens (MHC)
The way blood groups antigens
are recognized is quite different from the recognition of the other type of transplantation barriers, the “Histocompatibility Antigens” (also known as transplantation antigens). They were first identified in transplantation experiments in mice and because at that
time, nothing was known about the nature of the antigens, the term “Histocompatibility Antigens” that stands for “molecules playing a role in tissue compatibility” (Greek: histo meaning tissue) simply refers to their role in transplantation reactions. A group of genes that encoded for antigens that caused a particularly fast rejection of histoincompatible skin grafts was then designated as the major histocompatibility complex (MHC).
- minor histocompatibility antigens (mHC)
Other
histocompatibility antigens caused a much slower skin rejection and were
consequently designated as minor histocompatibility antigens (mHC).
Role and recognition of the alloantigenic structures in transplantations
Which type of alloantigenic structure represents the strongest (+++) transplantation barrier depends on the type of transplantation:
Like transplantations, blood transfusion is restricted by barriers of allo-immune reactions. Natural antibodies, that is antibodies that exist without prior immunization may recognize blood group antigens. Other antigens on red blood cells induce immune responses, stronger or weaker depending on the nature and quantity of the antigen and represent barriers on the second infusion. Matching of major and minor histocompatibility are irrelevant for the transfusion of blood. Immune reactions are thus only induced by an antibody-antigen recognition. Read more...
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