Chapter 21
The Immune System: Innate and Adaptive Body Defenses
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21
Ag-infected
body cell engulfed
by dendritic cell
Becomes
Activates
Activates
Induce
co-stimulation
Free Ags
may directly
activate B cell
Naive
CD4
T cells
Activated to clone
and give rise to
Naive
CD8
T cells
Antigen-
activated
B cells
Activated to clone
and give rise to
Cytokines stimulate
Cytotoxic
T cells
Memory
CD4
T cells
Helper
T cells
Memory
CD8
T cells
Together the nonspecific killers
and cytotoxic T cells mount a
physical attack on the Ag
Nonspecific killers
(macrophages and
NK cells of innate
immunity)
Circulating lgs along with complement
mount a chemical attack on the Ag
Antibodies (Igs)
Secrete
Plasma cells
(effector B cells)
Memory
B cells
Clone and
give rise to
Inhibits
Inhibits
Antigen (Ag) intruder
Innate defenses
Surface
barriers
Internal
defenses
Adaptive defenses
Triggers
Ag-presenting cell
(APC) presents
self-Ag complex
Co-stimulate and release cytokines
Present Ag to activated helper T cells
Cellular
immunity
Humoral
immunity
Figure 21.20
Simplified summary of the primary immune response.
Co-stimulation
usually requires direct cell-cell interactions; cytokines enhance these and many other events.
Although complement, NK cells, and phagocytes are innate defenses, they are enlisted in the
fight by cytokines. (For simplicity, only B cell receptors are illustrated.)
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