544
UNIT FOUR
neither A nor B. An individual with only antigen A has
type
A blood;
a person with only antigen B has
type B blood;
one
with both antigen A and antigen B has
type AB blood;
and
one with neither antigen A nor antigen B has
type O blood.
Table 14.11
indicates some of the frequencies of ABO blood
types in the diverse population of the United States.
ABO blood group antibodies are synthesized in the plasma
about two to eight months following birth. The stimulus for
their synthesis has not clearly been established. However, we
know that whenever antigen A is absent in the red blood cells,
an antibody called
anti-A
is produced, and whenever anti-
gen B is absent, an antibody called
anti-B
is manufactured.
Therefore, persons with type A blood also have anti-B anti-
body in their plasma; those with type B blood have anti-A
antibody; those with type AB blood have neither antibody;
and those with type O blood have both anti-A and anti-B anti-
bodies
(fig. 14.21
and
table 14.12)
. The anti-A and anti-B
antibodies are large and do not cross the placenta. Thus, if
a pregnant woman and her fetus are of different ABO blood
types, agglutination in the fetus will not occur.
The major concern in blood transfusion procedures is
that the cells in the donated blood not clump due to anti-
bodies in the recipient’s plasma. For example, a person with
type A blood must not receive blood of type B or AB, either
of which would clump in the presence of anti-B antibodies in
the recipient’s type A blood
(± g. 14.22)
. Likewise, a person
with type B blood must not be given type A or AB blood, and
a person with type O blood must not be given type A, B, or
AB blood.
14.5
BLOOD GROUPS
AND TRANSFUSIONS
Early blood transfusion experiments, which date from the
late 1600s, used lamb blood. By the 1800s, human blood was
being used with unpredictable results—some recipients were
cured, but some were killed when their kidneys failed under
the strain of handling clumping red blood cells when blood
types were incompatible. So poor was the success rate that,
by the late 1800s, many nations banned transfusions.
Around this time, Austrian physician Karl Landsteiner
began investigating why transfusions sometimes worked and
sometimes did not. In 1900, he determined that blood was of
differing types and that only certain combinations of them
were compatible. In 1910, identi±
cation of the ABO blood
antigen gene explained the observed blood type incompat-
ibilities. Today, thirty-one different genes are known to
contribute to the surface features of red blood cells, which
determine compatibility between blood types.
Antigens and Antibodies
The clumping of red blood cells when testing blood com-
patibility or resulting from a transfusion reaction is called
agglutination
(ah-gloo
˘na
shun). This phenomenon is due
to a reaction between red blood cell surface molecules called
antigens
(an
ti-jenz), formerly called
agglutinogens,
and pro-
tein
antibodies
(an
ti-bod
ez), formerly called
agglutinins,
carried in the plasma. Antibodies are called
anti-
because
they are “against” speci±
c antigens. Although many different
antigens are associated with human erythrocytes, only a few
of them are likely to produce serious transfusion reactions.
These include the antigens of the ABO group and those of
the Rh group. Avoiding the mixture of certain types of anti-
gens and antibodies prevents adverse transfusion reactions.
From Science to Technology 14.l discusses a DNA chip that
prevents transfusion mismatches.
A mismatched blood transfusion quickly produces telltale signs of
agglutination—anxiety; breathing difficulty; facial flushing; head-
ache; and severe pain in the neck, chest, and lumbar area. Red blood
cells burst, releasing free hemoglobin. Macrophages phagocytize the
hemoglobin, breaking it down into heme and globin. Some of the
heme is recycled. The rest of the heme is converted to bilirubin, which
may suF
ciently accumulate to cause the yellow skin of jaundice. ±ree
hemoglobin in the kidneys may ultimately cause them to fail.
ABO Blood Group
The
ABO blood group
is based on the presence (or absence)
of two major antigens on red blood cell membranes—
anti-
gen A
and
antigen B.
A person’s erythrocytes have one of
four antigen combinations: only A, only B, both A and B, or
TABLE
14.11
|
Some ABO Blood Type
Frequencies (%) in the
United States
Population
Type O
Type A
Type B
Type AB
Caucasian
45
40
11
4
African American
49
27
20
4
Native American
79
16
4
1
Hispanic
63
14
20
3
Chinese American
42
27
25
6
Japanese American
31
38
21
10
Korean American
32
28
30
10
TABLE
14.12
|
Antigens and Antibodies of
the ABO Blood Group
Blood Type
Antigen
Antibody
A
A
anti-B
B
B
anti-A
AB
A and B
Neither anti-A nor anti-B
O
Neither A nor B
Both anti-A and anti-B
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