BOX 1-3ABO Blood Groups

One of the most familiar ways in which the glycan information of a cell influences phenotype is the ABO blood grouping, which is a significant factor in determining which blood transfusions can be carried out. With rare exceptions, human red blood cells contain on their surfaces a core carbohydrate sequence (called the “H antigen”). The familiar ABO blood types derive from further modifications to this H carbohydrate chain. In the genome, the locus that determines ABO type encodes for a glycosyltransferase. Different variants of this enzyme either are non-functional and therefore don't alter the H carbohydrate (type O) or add slightly different sugars to it (type A and type B; see image). Because a person receives DNA from both parents, the four possible blood types are O, A, B, and AB. Immune antibodies can form against the types of sugar chains that an individual does not have on his or her red blood cells. Thus, a person with type O blood may form anti-A and anti-B antibodies that prevent him or her from successfully receiving blood from anyone other than a similar type O donor. On the other hand, a person with both type A and type B carbohydrate chains will not form antibodies against either and can receive blood from any ABO source. As a caveat, it is important to recognize that the ABO system is not the only factor that determines transfusion acceptance and thus the above description is not absolute. For example, humans also have red blood cell proteins that influence transfusion acceptance (for example, Rh factor). However, the ABO system helps illustrate how small differences in glycans translate to practical, physiological differences. The possibility of modifying the surface glycans on red blood cells to avoid ABO incompatibilities is also being explored (Olsson and Clausen 2008; Liu et al. 2007).

Representation of the glycans that form ABO blood group antigens. Triangles and circles represent different sugars units that make up these antigens; the figure also shows the types of chemical linkages that connect the sugar units

Representation of ABO sugars on red blood cells

SOURCE: Varki et al 2009, used with permission.

From: 1, Introduction

Cover of Transforming Glycoscience
Transforming Glycoscience: A Roadmap for the Future.
National Research Council (US) Committee on Assessing the Importance and Impact of Glycomics and Glycosciences.
Washington (DC): National Academies Press (US); 2012.
Copyright © 2012, National Academy of Sciences.

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