The ABO Group

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Figure 18.13 Charles Drew (1904-50).

recipients with compatible blood types. Plasma could be stored longer and was less likely to cause transfusion reactions.

When the U.S. War Department issued a directive forbidding the mixing of Caucasian and Negro blood in military blood banks, Drew denounced the order and resigned his position. He became a professor of surgery at Howard University in Washington, D.C., and later chief of staff at Freedmen's Hospital. He was a mentor for numerous young black physicians and campaigned to get them accepted into the medical community. The American Medical Association, however, firmly refused to admit black members, even Drew himself.

Late one night in 1950, Drew and three colleagues set out to volunteer their medical services to an annual free clinic in Tuskegee, Alabama. Drew fell asleep at the wheel and was critically injured in the resulting accident. Doctors at the nearest hospital administered blood and attempted unsuccessfully to revive him. For all the lives he saved through his pioneering work in blood transfusion, Drew himself bled to death at the age of 45.

All cells have an inherited combination of proteins, glycoproteins, and glycolipids on their surfaces. These function as antigens that enable our immune system to distinguish our own cells from foreign invaders. Part of the immune response is the production of 7 globulins called antibodies to combat the invader. In blood typing, the antigens of RBC surfaces are also called agglutinogens (ah-glue-TIN-oh-jens) because they are partially responsible for RBC agglutination in mismatched transfusions. The plasma antibodies that react against them are also called agglutinins (ah-GLUE-tih-nins).

Blood types A, B, AB, and O form the ABO blood group (table 18.7). Your ABO blood type is determined by the hereditary presence or absence of antigens A and B on your RBCs. The genetic determination of blood types is explained on page 148. The antigens are glycoproteins and glyco-lipids—membrane proteins and phospholipids with short carbohydrate chains bonded to them. Figure 18.14 shows how these carbohydrates determine the ABO blood types.

_Think About It_

Suppose you could develop an enzyme that selectively split N-acetylgalactosamine off the glycolipid of type A blood cells (fig. 18.14). What would be the potential benefit of this product to blood banking and transfusion?

The antibodies of the ABO group begin to appear in the plasma 2 to 8 months after birth. They reach their maximum concentrations between 8 and 10 years of age and then slowly decline for the rest of one's life. They are produced mainly in response to the bacteria that inhabit our intestines, but they cross-react with RBC antigens and are therefore best known for their significance in transfusions.

Abo Blood Group Glycolipids

Figure 18.14 Chemical Basis of the ABO Blood Types. The terminal carbohydrates of the antigenic glycolipids are shown. All of them end with galactose and fucose (not to be confused with fructose). In type A, the galactose also has an N-acetylgalactosamine added to it; in type B, it has another galactose; and in type AB, both of these chain types are present.

Figure 18.14 Chemical Basis of the ABO Blood Types. The terminal carbohydrates of the antigenic glycolipids are shown. All of them end with galactose and fucose (not to be confused with fructose). In type A, the galactose also has an N-acetylgalactosamine added to it; in type B, it has another galactose; and in type AB, both of these chain types are present.

Saladin: Anatomy & I 18. The Circulatory System: I Text I © The McGraw-Hill

Physiology: The Unity of Blood Companies, 2003 Form and Function, Third Edition

696 Part Four Regulation and Maintenance

Table 18.7 The ABO Blood Group

ABO Blood Type

Type O

Type A

Type B

Type AB

Possible Genotypes

ii

IaIa, / a/

/bIb, /b/

/a /b

RBC Antigen

None

A

B

A,B

Plasma Antibody

Anti-A, anti-B

Anti-B

Anti-A

None

Compatible Donor RBCs

O

O, A

O, B

O, A, B, AB

Incompatible Donor RBCs

A, B, AB

B, AB

A, AB

None

Frequency in U.S. Population

White

45%

40%

11%

4%

Black

49%

27%

20%

4%

Hispanic

63%

14%

20%

3%

Japanese

31%

38%

22%

9%

Native American

79%

16%

4%

<1%

AB antibodies react against any AB antigen except those on one's own RBCs. The antibody that reacts against antigen A is called a agglutinin, or anti-A; it is present in the plasma of people with type O or type B blood—that is, anyone who does not possess antigen A. The antibody that reacts against antigen B is p agglutinin, or anti-B, and is present in type O and type A individuals—those who do not possess antigen B. Each antibody molecule has 10 binding sites where it can attach to either an A or B antigen. An antibody can therefore attach to several RBCs at once and bind them together (fig. 18.15). Agglutination is the clumping of RBCs bound together by antibodies.

A person's ABO blood type can be determined by placing one drop of blood in a pool of anti-A serum and another drop in a pool of anti-B serum. Blood type AB exhibits conspicuous agglutination in both antisera; type A or B agglutinates only in the corresponding antiserum; and type O does not agglutinate in either one (fig. 18.16).

Type O blood is the most common and AB is the rarest in the United States. Percentages differ from one region of the world to another and among ethnic groups because people tend to marry within their locality and ethnic group and perpetuate statistical variations particular to that group.

In giving transfusions, it is imperative that the donor's RBCs not agglutinate as they enter the recipient's bloodstream. For example, if type B blood were transfused into a type A recipient, the recipient's anti-B antibodies would immediately agglutinate the donor's RBCs (fig. 18.17). A mismatched transfusion causes a transfusion reaction—the agglutinated RBCs block small blood vessels, hemolyze, and release their hemoglobin over the next few hours to days. Free hemoglobin can block the kidney tubules and cause death from acute renal failure within a

Blood Agglutination
Figure 18.15 Agglutination of RBCs by an Antibody. Anti-A and anti-B have 10 binding sites, located at the 2 tips of each of the 5 Ys, and can therefore bind multiple RBCs to each other.

week or so. For this reason, a person with type A (anti-B) blood must never be given a transfusion of type B or AB blood. A person with type B (anti-A) must never receive type A or AB blood. Type O (anti-A and anti-B) individuals cannot safely receive type A, B, or AB blood.

Type AB is sometimes called the universal recipient because this blood type lacks both anti-A and anti-B antibodies; thus, it will not agglutinate donor RBCs of any ABO type. However, this overlooks the fact that the donor's plasma can agglutinate the recipient's RBCs if it contains anti-A, anti-B, or both. For similar reasons, type O is sometimes called the universal donor. The plasma of a type O donor, however, can agglutinate the RBCs of a type A, B, or AB recipient. There are procedures for reduc-

Saladin: Anatomy & I 18. The Circulatory System: I Text I © The McGraw-Hill

Physiology: The Unity of Blood Companies, 2003 Form and Function, Third Edition

Saladin Blood Types

Figure 18.16 ABO Blood Typing. Each row shows the appearance of a drop of blood mixed with anti-A and anti-B antisera. Blood cells become clumped if they possess the antigens for the antiserum (top row left, second row right, third row both) but otherwise remain uniformly mixed. Thus type A agglutinates only in anti-A; type B agglutinates only in anti-B; type AB agglutinates in both; and type O agglutinates in neither of them.

Figure 18.16 ABO Blood Typing. Each row shows the appearance of a drop of blood mixed with anti-A and anti-B antisera. Blood cells become clumped if they possess the antigens for the antiserum (top row left, second row right, third row both) but otherwise remain uniformly mixed. Thus type A agglutinates only in anti-A; type B agglutinates only in anti-B; type AB agglutinates in both; and type O agglutinates in neither of them.

Agglutination Blood
Figure 18.17 Effects of a Mismatched Transfusion. Donor RBCs become agglutinated in the recipient's blood plasma. The agglutinated RBCs lodge in smaller blood vessels downstream from this point and cut off the blood flow to vital tissues.

Chapter 18 The Circulatory System: Blood 697

ing the risk of a transfusion reaction in certain mismatches, however, such as giving packed RBCs with a minimum of plasma.

Contrary to some people's belief, blood type is not changed by transfusion. It is fixed at conception and remains the same for life.

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Responses

  • RITVA KORTEKANGAS
    What would be the benefit of splitting nacetylgalactosamine off of type a blood?
    8 years ago

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