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BIO 156
Chapter 14
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The Immune System
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Viruses
Viruses are nonlivingbiological agents that
invade cells.
Viruses consist of
a nucleic acid core
a coat of protein
molecules called thecapsid.
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Viruses Are Grouped by Their Shape
Helical viruses have helical symmetry
Icosahedral viruses have isocahedral symmetry
Viruses that have both helical and icosahedral
symmetry have complex symmetry
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Rabies
Helical VirusHerpes, Icosahedral Virus
Smallpox
Complex Virus
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Bacteria Many bacteria perform usefulfunctions, while others cause
serious diseases.
Bacteria are classified living
organisms that reproduce on
their own without taking over
host cells.
Bacteria respond to
antibiotics although many
have become resistant tocommonly used antibiotics;
viruses do not, but new
antiviral drugs may help flu
sufferers.
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E. coli
S. aureus
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The Bodies First Line of Defense
In humans, the first line of defense is a physicaland chemical barrier.
Physical
the skin epithelial linings of the respiratory, digestive,
and urinary systems
Chemical
Body secretions that impair bacterial growth
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The bodys second line of defense combatsinfectious agents that penetrate the first line
and consists of cellular and chemical
responses.
Four nonspecific mechanisms include the
inflammatory response, pyrogens,
interferons, and complement.
The Bodies Second Line of Defense
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The Inflammatory Response
The inflammatory response involves
a chemical and cellular responses. Macrophages, cells derived fromthe monocyte, are found inconnective tissue beneath epithelia,where they phagocytize infectiousagents, preventing their spread.
Histamine, a chemical released by
damaged tissue, stimulates
arterioles in the infected tissue to
dilate.
The increase in blood flow raises
the temperature of the wound.
Heat stimulates macrophage
metabolism, accelerating the rate of
the destruction of infectious agents.
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The cells of the immune system, lymphocytes,selectively target foreign substances and foreignorganisms.
Lymphocytes circulate in the blood and lymphand take up residence in the lymphoid organs andlymphoid tissues.
The Third Line of Defense:
The Immune System
Substances that trigger an immune response
are large molecular weight molecules,particularly proteins and polysaccharides,
called antigens.
-Antigens are antibody-generating substances.
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Immature B and T cells are incapable of responding to
antigens but soon gain this ability.
B cells mature and differentiate in the bone marrow. T cells mature in the thymus.
B cells provide humoral immunity through the production of
antibodies. Antibodies are proteins that bind to specific antigens.
When T and B cells first encounter an antigen, the
primary response, they react slowly.
The rapidity of the secondary response is the result of theproduction of memory cells during the primary response.
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B cell Activation
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B cell Activation Continued
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Primary and Secondary Antibody Responses
Antibody Structure
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Antibodiesdestroy
antigens in one
of four ways:
Neutralization
Agglutination
Precipitation
Activation of thecomplement
system
How Antibodies Work
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T cells attack foreign cells directly.
T cells differentiate into at least four cell types, each
with a separate function in cell-mediated immunity.Cytotoxic T cellsMemory T cellsHelper T cells
Suppressor T cells
T cells
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The outer membrane of the tumor
cell (right) has been shot full of holes
by a protein, perforin, secreted from
the cytotoxic cell (left). The tumor
target cell has become leaky and aninflux of water has made it expand in
volume; it has also lost many of its
surface villi. In addition, there is a
large cavity in the membrane of the
tumor target cell.
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Macrophages play a very important role in humoral and cell-
mediated immunity.
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HIV
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HIV
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HIV
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Course of HIV Infection
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Kaposis Sarcoma
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Azidotheymidine (AZT) was the first drug used for
treatment
It interferes with reverse transcriptase activity
HIV can become resistant to some antivirals
This requires a cocktail of drugs called highly active antiretroviral
therapy (HAART)
HAART reduces the risk of HIV transmission and can extend life of
patients by about 8 years
A vaccine has not yet been developed
HIV continually mutates and recombines, making vaccinedevelopment difficult
A vaccine needs to activate T lymphocytes, which are the cells
infected by the virus
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HAART
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End of Chapter 14