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.
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.
- 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). Read more...
- minor histocompatibility antigens (mHC)
Other
histocompatibility antigens caused a much slower skin rejection and were
consequently designated as minor histocompatibility antigens (mHC).
Read more...
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:
The response to histoincompatible tissues (incompatible MHC and/or mHC) was designated as allorecognition. Histocompatibility antigens can be recognized by (allo)antibodies and by T cells. Allorecognition at the basis of a rejection of an organ have many points in common with the allorecognition causing Graft versus Host Disease. The response is initiated when alloantigens expressed by the stimulator are recognized by so called "alloreactive" T cells of the responder.
Read more ...
Which histocompatibility antigen is recognized and whether the antibody or T cell response prevails depends on the type of transplantation as well as of the degree of matching betweeen stimulator and responder. Read more...
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