All ABO Blood Types

These diagrams show red blood cells of each type with all their ABO antigens in place. The representation of the red blood cell shows it a great deal smaller than it actually is in comparison to the antigens for reason of space. It is huge compared to the antigens, which would not even be visible on the surface. There are 30 different blood types whose antigens also appear on each blood cell, as well as various receptors, proteins, glycoproteins, etc., but these have been left off of the diagrams as it would be impossible to depict all of these different structures within this small space. For clarity, these show ABO antigens only.

ABH antigens are not only found in humans, but also in various organisms such as bacteria, plants, and animals. ABH substances are present both on red blood cells and in secretions only in humans and some of the apes (chimpanzee, gorilla, orangutan, and gibbon). In all other mammalian species these substances are found only in secretions.

The product of the A gene is alpha 1,3-Nacetylgalactosaminyltransferase. This transferase is an enzyme which forms the blood group A specific antigen by 'transferring' N-acetylgalactosamine residues onto H determinant (or, onto the 'O' antigen base). The B gene product is an alpha 1,3-galactosyltransferase. This enzyme forms the B specific antigen by transferring alpha-galactose onto the H determinant. The O gene is silent, or inactive. It carries no information to create a working glycosyltransferase. So the H substance, which is the precursor of both the A and B antigens, remains as it is, the O antigen.

The average number of ABH sites on each human red blood cell are in the range of 1.5 to 2.0 million. There are differences in the number of blood group determinants (antigens) in the various subgroups. Within the many A subgroups, the number of A antigens varies from a range of close to1-1.5 million on A1 red blood cells, to fewer than 2,000 on Am and Ael red blood cells. The B subgroups are much rarer than the A subgroups. These subgroups have not been as well defined as the A subgroups yet. In AB individuals, the A and/or the B activities of the red blood cells are usually lower than what is found in A or B individuals. So A1B red blood cells have far fewer A and B sites than A1 or B cells. If a stronger A or B is combined with a weak form of B or A, the expression may be changed by depressing activity of the weaker allele. That is why an A2B is sometimes expressed as A3B.

ABO Antigens

A1	A1B
B	A2B
O	A2

Table showing Number of A,B, O, Antigen sites for each ABO Blood Type in order of O Antigens Sites>

Blood Group	A sites	B sites	O sites
O	-	-	1,590,000-1,740,000
A2	160,000-290,000	-	1,080,000-1,210,000
B	-	610,000-830,000	540,000-760,000
A2B	120,000 - 200,000	450,000-550,000	300,000-500,000
A1	910,000-1,300,000	-	70,000-170,000
A1B	420,000-850,000	310,000-560,000	20,000-70,000

Structure of each ABO Antigen

O (H) Antigen [Precursor of A and B antigens]
A Antigen
B Antigen

Units of the ABO Antigens shown above

Ceramide	Glucose	Galactose	N-acetyl glucosamine	Fucose	N-acetyl galactosamine

Thanks to F. Yamamoto, Ph.D. of the Burnham Institute, Torrey Pines, Calif. for his help in calculating the number of O (H) antigen sites for the different blood types.