Defense Mechanisms of the Body
659
Encounter and recognition
Activation
Attack
+
Plasma cells
B cell
Helper T cell
Cytotoxic T cell
(Cytokines)
(Cytokines)
Guide phagocytes,
complement, and
NK cells to attack
antigen-bearing cells
or to neutralize
free antigen
Directly attack antigen-
bearing cells
Antibodies
+
Begin
Antigen
Specific antigen-
binding sites
One “prong”
Light
chain
Heavy chain
Fc
(“stem”)
Variable
ends
Constant ends
Figure 18–9
Summary of the roles of B, cytotoxic T, and helper T cells in immune responses. Events of the attack phase are described in later sections.
The
B
symbol denotes a stimulatory effect (activation) of cytokines.
Figure 18–10
Immunoglobulin structure. The Fc portions and an extended region
of the heavy chains are the same for all immunoglobulins of a
particular class. A small portion of the light chains are also the same
for a given immunoglobulin class. Collectively, these portions of
the heavy and light chains are called “constant ends.” Each “prong”
contains a variable amino acid sequence, which represents the single
antigen binding site. The links between chains represent disulfi de
bonds.
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