ABSTRACT
The discovery of the ABO system at the end of the nineteenth century laid the foundation for clinical transfusion practice. It is now known that ABO antigens expressed on red cells are determined by genes located on the long arm of chro mosome nine. These genes code for glycosyl transferases, which attach different carbohydrates (sugars), to a terminal galactose of an oligosaccharide chain. These oligosaccharide chains are attached to phospholipids in the red cell membrane and to proteins (glycoproteins) in plasma. The ABO system is illustrated in Fig ure 6.1. In blood group A, the terminal sugar is N-acetyl D-galactosamine and in blood group B, D-galactose. Individuals o f blood group AB contain both A and В antigens on their red cells. Individuals o f blood group O lack a functional trans ferase and hence do not transfer either sugar o f type A or B. The distribution of the different ABO types differs substantially between different populations as il lustrated in Figure 6.1. Prominent is the relatively larger proportion o f Group В in African-Americans and Asians.
