146 Chapter 8
Whole blood may be used for a transfusion, but
usually donor blood is processed to remove some of
its components, such as white blood cells. Research
this topic at the National Institutes of Health website
(www.nih.gov). Why are white blood cells or other
elements of whole blood potentially a problem in
transfused blood?ThiNk OuTsiDE ThE bOOk
blood types: genetically different red blood Cells
people have type O red blood cells—they have neither A
nor B markers. Depending on your ABO blood type, your
blood plasma also will contain antibodies to other blood
types, even if you have never been exposed to them. As
the chapter introduction noted, a severe immune response
takes place when incompatible blood types are mixed. This
is why donated blood must undergo the chemical analysis
called ABO blood typing.mixing incompatible blood types can cause
the clumping called agglutination
As you can see in Table 8.1, if you are type A, your body
doesn’t have antibodies against A markers but does have
them against B markers. If you are type B, you don’t have
antibodies against B markers, but you do have antibodies
against A markers. If you are type AB, you do not have
antibodies against either form of the marker. If you are
type O, however, you have antibodies against both forms
of the marker, so you can only receive blood from another
type O individual.
In theory, type O people are “universal donors,” because
they have neither A nor B antigens, and—again, only in
theory—type AB people are “universal recipients.” In fact,
however, as already noted, there are many markers associ-
ated with our red blood cells, and any of them can trigger a
defense response in which the recipient’s antibodies attack
the donor’s blood cells. This defense response is called
agglutination (Figure 8.5). When the mixing of incom-
patible blood causes agglutination, antibodies act againstn The different human blood types are due to variations in
the surface markers on red blood cells.n Link to Plasma membrane 3.4
Each of your body cells has markers on its surface that
mark the cell as “self.” Your genes have determined the
chemical characteristics of these self markers, which
vary from person to person. The variations are medically
important because the markers on cells and substances
that are not part of an individual’s own body are antigens.
An antigen is a chemical characteristic of a cell, particle,
or substance that causes the immune system to mount
an immune response. Defensive proteins called antibodies
identify and attach to antigens in a process that is a major
topic of Chapter 9. For now, it’s important to know that for
each type of antigen, the body makes a specific type of
antibody that can bind to it.
To date, biologists have identified more than thirty com-
mon self markers on human red blood cells, and hundreds
more rare ones. Because each kind of marker can have
several forms, the different forms are often called “blood
groups.” Two of them, the Rh blood group and the ABO
blood group, are extremely important in situations where
the blood of two people mixes. We will consider the Rh
blood group in Section 8.5. For now, let’s look more closely
at the ABO blood group, which is a vital consideration in
blood transfusions.
self markers on red blood cells include
the abo group of blood types
One of our genes carries the instructions for building the
ABO self markers on red blood cells. Different versions of
this gene carry instructions for different markers, called
type A and type B. A third version of the gene does not call
for a marker, and red blood cells of someone who has this
gene are dubbed type O. Together, these markers make up
the ABO blood group (Table 8.1).
In type A blood, red blood cells bear A markers. Type
B blood has B markers, and type AB has both A and B.
Type AB blood is quite rare, but a large percentage of
8.4
Antigens
on Plasma
Blood Membranes Antibodies Safe to Transfuse
Type of RBCs in Blood To From
A A Anti-B A, AB A, O
B B Anti-A B, AB B, O
AB A 1 B none AB A, B, AB, O
O — Anti-A, A, B, AB, O O
Anti-BTable 8.1 Animated! AbO blood Types© Wei Ming/
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