Essentials of Anatomy and Physiology

produced is specific for only one antigen. Because
there are so many different pathogens, you might
think that the immune system would have to be capa-
ble of producing many different antibodies, and in fact
this is so. It is estimated that millions of different anti-
gen-specific antibodies can be produced, should there

be a need for them. The structure of antibodies is

shown in Fig. 14–8, and the five classes of antibodies

are described in Table 14–1.

The antibodies produced will bond to the antigen,

forming an antigen–antibody complex. This complex

results in opsonization, which means that the antigen

The Lymphatic System and Immunity 333

Table 14–1 CLASSES OF ANTIBODIES

Name Location Functions

IgG

IgA

IgM

IgD

IgE

Blood

Extracellular fluid

External secretions (tears,

saliva, etc.)

Blood

B lymphocytes

Mast cells or basophils

• Crosses the placenta to provide passive immunity for newborns


• Provides long-term immunity following recovery or a vaccine


• Present in breast milk to provide passive immunity for breast-fed infants


• Found in secretions of all mucous membranes


• Produced first by the maturing immune system of infants


• Produced first during an infection (IgG production follows)


• Part of the ABO blood group


• Receptors on B lymphocytes


• Important in allergic reactions (mast cells release histamine)

A

Antigen binding

site

Complement

binding site

Macrophage

binding site

B

IgG IgD IgE

IgA

IgM

Bacteria Virus Toxin

Agglutination

C

Neutralization

Disulfide

bonds

Figure 14–8. Antibodies.
(A) Structure of one IgG mol-
ecule. Notice how the many
disulfide bonds maintain the
shape of the molecule.
(B) Structure of the five classes
of antibodies. (C) Antibody
activity: Agglutination of bac-
teria and neutralization of
viruses or toxins.
QUESTION:In part C, why
does neutralization inactivate
a bacterial toxin?