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Monday, December 26, 2016

TRANSPLANTATION IMMUNOGENETICS OF HLA

A person’s human leukocyte antigen (HLA) type is like a barcode on the immune system’s cells

A person’s human leukocyte antigen (HLA) type is like a barcode on the immune system’s cells



Major Histocompatibility Complex


Embedded in the membrane of every human cell is an array of molecules (many of them glycoprotein) that are recognized by the immune system of another human as antigens. Normally, the body's immune system does not respond to its own membrane antigens because they are self.

Transplanted foreign cells, however, carry non-self membrane antigens that can be recognized, and following this recognition, the cells carrying those antigens can be destroyed. 

Thus, for a successful transplant, there must be animal differences between the antigens of the recipient and the donor, for example, the individuals must be histocompatible. Unfortunately, of course, the search for compatibility requires an understanding of the genetic control of histocompatibility antigens.

A small segment of the chromosome is referred to as the major histocompatibility complex (MHC) and encodes within it the strongest histocompatibility, or transplantation, antigens. This complex of deoxyribonucleic acid (DNA) comprises approximately 1/1000 of all genetic material.

These are the antigens that, if recognized as foreign in cells of an allograft, lead to rapid destruction of the allograft. Various aspects of the major histocompatibility complex in humans referred to as HLA. 

Besides these very strong transplantation antigens, a number of other immunologically related phenomena are controlled by, or at least influenced by genes located in the MHC, for example, immune responsiveness (Ir), susceptibility to some diseases, various components of the complement system, and cell-mediated responses against virally infected autologous or syngeneic cells.

The evidence for immune responsiveness in humans is still fragmentary, although the MHC includes Ir genes in several other species, for example, mouse, guinea pig, rat, and rhesus monkey.


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