7/28/2019 Blood Group Ass

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Blood groups are created by molecules present on the surface of red blood cells (and often on

other cells as well).

The ABO Blood Groups

The ABO blood groups were the first to be discovered (in 1900) and are the most important inassuring safe blood transfusions.

The table shows the four ABOphenotypes("blood groups") present in the human population and

thegenotypesthat give rise to them.

Blood

Group

Antigens

on

RBCs

Antibodies in

SerumGenotypes

A A Anti-B AA orAO

B B Anti-A BB orBO

AB A and B Neither AB

O Neither Anti-A and Anti-B OO

Whenred blood cellscarrying one or bothantigensare exposed to the correspondingantibodies,

they agglutinate; that is, clump together. People usually have antibodies against those red cellantigens that they lack.

The antigens in the ABO system areO-linked glycoproteinswith their sugar residues exposed atthe cell surface. The terminal sugar determines whether the antigen is A or B.

The critical principle to be followed is that transfused blood must not contain red cells that the

recipient's antibodies can clump. Although theoretically it is possible to transfuse group O blood

into any recipient, the antibodies in the donated plasma can damage the recipient's red cells.

Thus, when possible, transfusions should be done with exactly-matched blood.

In 2007, Danish and French investigators reported the properties of two bacterial glycosidases

that specifically remove the sugars responsible for the A and B antigens. This discovery raisesthe possibility of being able to treat A, B, or AB blood with these enzymes and thus convert the

blood to Group O, the "universal donor".

Why do we have antibodies against red cell antigens that we lack? Bacteria living in ourintestine, and probably some foods, expressepitopessimilar to those on A and B. We synthesize

antibodies against these if we do not have the corresponding epitopes; that is, if our immune

system sees them as "foreign" rather than "self".

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7/28/2019 Blood Group Ass

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A blood type (also called a blood group) is a classification ofbloodbased on the presence orabsence ofinheritedantigenicsubstances on the surface ofred blood cells(RBCs). These

antigens may beproteins,carbohydrates,glycoproteins, orglycolipids, depending on the blood

group system. Some of these antigens are also present on the surface of other types ofcellsofvarioustissues. Several of these red blood cell surface antigens that stem from oneallele(or very

closely linkedgenes), collectively form a blood group system.

[1]

Blood types areinheritedandrepresent contributions from both parents. A total of 30human blood group systemsare nowrecognized by theInternational Society of Blood Transfusion(ISBT).

[2]

Manypregnantwomen carry afetuswith a different blood type from their own, and the mother

can form antibodies against fetal RBCs. Sometimes these maternal antibodies areIgG, a small

immunoglobulin, which can cross the placenta and causehemolysisof fetal RBCs, which in turn

can lead tohemolytic disease of the newborn, an illness oflow fetal blood countsthat rangesfrom mild to severe.

[3]

Blood type (or blood group) is determined, in part, by the ABO blood group antigens

present on red blood cells.

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