Alloimmunity

Alloimmunity is a condition in which the body gains immunity, from another individual of the same species, against its own cells. Alloimmunity should not be confused with autoimmunity in which the body's immune system attacks its own cells without being provoked or influenced by substances or cells from another member of the same species.

An alloantigen is an antigen that is a part of an animal's self-recognition system. e.g., Major histocompatibility complex molecules. When injected into another animal, they trigger an immune response aimed at eliminating them. Therefore, it can be thought of as an antigen that is present in some members of the same species, but is not common to all members of that species. If an alloantigen is presented to a member of the same species that does not have the alloantigen, it will be recognized as foreign. They are the products of polymorphic genes. [Abbas AK and Lichtman AH. Basic Immunology: Functions and Disorders of the Immune System. Second Edition, Updated Edition 2006-2007. Elsevier Saunders Publishing.]

One alloantigen is known as "Qa-1".cite journal |author=Germana S, Shinohara N |title=Qa-1/Tla region alloantigen-specific CTL with alpha beta receptor |journal=Immunology |volume=74 |issue=4 |pages=578–82 |year=1991 |month=December |pmid=1838350 |pmc=1384763 |doi= |url=]

If either alloimmunity or autoimmunity is directed against red blood cells (RBCs), the direct Coombs test is positive.

Alloimmunity can occur
*in the recipient after transfusions of fluids such as blood or plasma.
*in the recipient after allografts (grafts).
*in the fetus after maternal antibodies have passed through the placenta into the fetus, as in haemolytic disease of the newborn and fetomaternal alloimmune thrombocytopenia.

ee also

* Isoantigen

References

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