631
CHAPTER SIXTEEN
Lymphatic System and Immunity
Cytokines
Activated helper
T cell interacts with
B cell (which has
combined with an
identical
antigen)
and releases
cytokines, which
activate the B cell
Helper T cell contacts
displayed antigen and
proliferates
Displayed
antigen
Antigen
B cells
Antigen
receptor
B cell combines
with antigen
Macrophage
displays digested
antigen on its
surface
Activated B cell
Helper
T cell
Helper
T cells
Interleukin-2
Cytotoxic
T cell
Cytotoxic
T cell
Cytotoxic
T cell
Memory
T cell
1
Cytotoxic
T cell contacts
displayed
antigen
3
2
Activated helper
T cell
interacts with cytotoxic
T cell (which has com-
bined with an identical
antigen) and releases
interleukin-2, which
activates the cytotoxic
T cell
4
Proliferation
and
Differentiation
5
(a)
Macrophage
Helper T cell
(b)
FIGURE 16.17
T and B cell activation. (
a
) During an
infection, macrophages bind to helper T cells, activating
them to trigger other immune defenses. (
b
) In the
photograph, the round cells are helper T cells, and the cells
bearing projections are macrophages (1,040×).
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