546
UNIT FOUR
14.1
FROM SCIENCE TO TECHNOLOGY
Blood Typing and Matching: From Serology to DNA Chips
T
yping and matching blood is essential to
minimize the chance that the immune
response of a blood transfusion recipient
will reject the blood. The popular view of blood
types is that it is a simple matter of A, B, AB, or O.
Rh blood types become important in pregnancy,
when woman and offspring may be incompat-
ible. However, human blood can be classified
into twenty-nine major types based on protein
and carbohydrate molecules (antigens) on the
surfaces of red blood cells. Each of these types
includes many subtypes, generating hundreds of
ways that the topographies of our red blood cells
diF
er from individual to individual.
±or more than a century, an approach called
serology has been used to type blood into major
groups by identifying red blood cell antigens.
DiF
erent reagents are required to detect diF
erent
antigens, and so typing by serology beyond a few
blood groups is costly and time consuming. It can
also miss variants of antigens that are small or
hidden among the embedded proteins and ema-
nating carbohydrate chains of the cell surface. A
more informative way to type blood is to identify
the
instructions
for the cell-surface antigens—the
genes that encode these proteins. This approach,
termed genotyping, is being tested in Europe and
Canada.
A consortium of European blood banks
and universities, called Bloodgen, is using a tiny
device called a BLOODchip that detects, with
one test, 100 distinct DNA “signatures” (²
g. 14D).
These represent some of the gene variant com-
binations that underlie blood types traditionally
defined by serology. So far the BLOODchip is
able to accurately type 99.8% of samples; serol-
ogy can accurately type 97%. Another device
called BeadChip tests for a different group of
antigens. Other variations on the DNA chip
theme are in development.
Accurate blood matching for many blood
groups may not be of great importance for the
average person who may require just one or two
transfusions in a lifetime. But for a person who
has a chronic disorder that requires multiple
transfusions—such as leukemia or sickle cell dis-
ease—greater speci²
city in typing and match-
ing blood can be lifesaving. Such individuals
produce so many antibodies (immune system
proteins) against so many types of donor blood
that it is often di³
cult to determine their blood
types by serology. DNA typing, however, can tell.
The head of the American Red Cross estimates
that DNA blood typing will be routine within ²
f-
teen years, but that serology is likely to remain a
valuable tool.
fused slowly and in limited amounts to minimize the chance
of an adverse reaction. When type O blood is given to blood
types A, B, or AB, it is generally transfused as “packed cells,”
meaning the plasma has been removed. This also minimizes
adverse reactions due to the anti-A and anti-B antibodies
found in the plasma of type O blood.
Table 14.13
summarizes
Type AB blood lacks both anti-A and anti-B antibodies,
so an AB person can receive a transfusion of blood of any
other type. For this reason, type AB persons are sometimes
called
universal recipients.
However, type A blood, type B
blood, and type O blood still contain antibodies (either
anti-A and/or anti-B) that could agglutinate type AB cells.
Consequently, even for AB individuals, it is always best to
use donor blood of the same type as the recipient blood. If
the matching type is not available and type A, B, or O is used,
it should be transfused slowly and in limited amounts so that
the recipient’s larger blood volume dilutes the donor blood.
This precaution usually avoids serious reactions between the
donor’s antibodies and the recipient’s antigens.
Type O blood lacks antigens A and B. Therefore, theoret-
ically this type could be transfused into persons with blood
of any other type. Individuals with type O blood are some-
times called
universal donors.
Type O blood, however, does
contain both anti-A and anti-B antibodies, and if it is given to
a person with blood type A, B, or AB, it too should be trans-
TABLE
14.13
|
Preferred and Permissible
Blood Types for Transfusions
Blood Type of
Recipient
Preferred Blood
Type of Donor
Permissible Blood Type of Donor
(In an Extreme Emergency)
AA
O
BB
O
AB
AB
A, B, O
O
O
No alternate types
FIGURE 14D
Bloodgen is a consortium
of European blood banks and universities
investigating the use of DNA microarrays
(“chips”) to type blood. Their logo is a drop of
blood superimposed on a DNA double helix.
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