633
CHAPTER SIXTEEN
Lymphatic System and Immunity
A single type of B cell carries information to produce a
single type of antibody. However, different B cells respond
to different antigens on a pathogen’s surface. Therefore,
an immune response may include several types of antibod-
ies manufactured against a single microbe or virus. This is
called a
polyclonal response.
From Science to Technology
16.1 discusses how researchers use clones of single B cells to
produce single, or monoclonal, antibodies.
The human body can manufacture an apparently limitless number
of different antibodies, but we have a limited number of antibody
genes. During the early development of B cells, sections of their anti-
body genes move to other chromosomal locations, creating new
genetic instructions for antibodies. The great diversity of antibody
types is increased further because different antibody protein sub-
units combine. Antibody diversity is like using the limited number of
words in a language to compose an inF
nite variety of stories.
Other members of the activated B cell’s clone differen-
tiate further into
plasma cells,
which produce and secrete
large globular proteins called
antibodies
(an
tı˘-bod
e
¯z) or
immunoglobulins
(im
u-no-glob
u-linz) similar in structure
to the antigen-receptor molecules on the original B cell’s
surface (±
g. 16.19). These antibodies can combine with the
antigen on the pathogen and react against it. A plasma cell
is an antibody factory, as evidenced by its characteristically
huge Golgi apparatus. At the peak of an infection, a plasma
cell may produce and secrete 2,000 antibody molecules per
second! Body fl
uids carry antibodies, which then react in
various ways to destroy speci±
c antigens or antigen-bear-
ing particles. This antibody-mediated immune response is
called the
humoral immune response
(“humoral” refers to
uid).
Table 16.6
summarizes the steps leading to antibody
production as a result of B and T cell activities. T cells can
suppress antibody formation by releasing cytokines that
inhibit B cell function.
Antigen
Receptor-antigen
combination
Activated
B cell
Endoplasmic
reticulum
Released
antibodies
Antigen
receptor
Plasma cell
(antibody-secreting cell)
Memory cell
(dormant cell)
Memory cell
(dormant cell)
Plasma cell
(antibody-secreting cell)
Proliferation
Proliferation and
Differentiation
Proliferation and
Differentiation
Cytokines
from helper
T cell
Clone of
B cells
Clone of
B cells
FIGURE 16.19
An activated B cell proliferates after stimulation by cytokines released by helper T cells. The B cell’s clone enlarges. Some cells of
the clone give rise to antibody-secreting plasma cells and others to dormant memory cells.
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