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Lecture 10Immune System
Lecture 10
1. Introduction
2. Nonspecific External Defenses
3. Innate Immune Response
4. Acquired Immune Response
5. Antibiotics and Vaccines
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The not-so-common cold
• A “cold” is an infection of
the mucus membranes of
the respiratory tract by a
rhinovirus.
• Over 100 rhinoviruses have
been identified, which is
one reason why we don’t
become immune to “the
cold.”
Virus vs. Bacteria
• Colds and influenza are
caused by viruses.
• Viruses are non-living
particles that contains genetic
material, they hijack your cells
to reproduce.
• Viruses cannot be “killed”
with antibiotics.
Rhinovirus
Influenza
virus
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Virus vs. Bacteria
• Bacteria are living organisms
that have a metabolism, have
DNA, and can reproduce on
their own.
• Bacteria can be killed with
antibiotics.
E. coli
Streptococcus
Fungi, Protista, & Worms!
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• Viruses, bacteria, fungi, protists, and worms are
everywhere. Some of them want to invade your body.
How does your body defend itself against them?
• Viruses and Bacteria
Immune System
Immune System: Body Defenses
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Defense Against Disease
1. Nonspecific External Barriers
2. Innate Immune System
3. Acquired (Adaptive) Immune System
Nonspecific External Barriers
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First Line of DefenseNon-Specific External Defenses are designed to
prevent infections by viruses and bacteria from
entering the body. These include:
• Intact skin
• Saliva in Mouth
• Mucus and Cilia
• Cough Reflex
• Stomach Acid
• Small Intestine –Bile
The Skin
• Dead skin cells are constantly
sloughed off, making it hard
for invading bacteria to
colonize.
• Sweat and oils contain anti-
microbial chemicals,
including some antibiotics.
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Saliva
Mucus and Cilia
• Mucus contains special enzymes
that destroy bacterial cell walls.
• The normal flow of mucus washes
bacteria and viruses off of mucus
membranes.
• Cilia in the respiratory tract move
mucus out of the lungs to keep
bacteria and viruses out.
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Cough Reflex
Coughing ejects mucus and
foreign matter from the lungs.
Coughs may be voluntary, but
more often in response to
stimulation of receptors in the
respiratory tract.
Stomach Acid
• Low pH. Stomach acid prevents
bacterial and fungal growth.
• When it is properly acidic, bacteria
that are ingested along with food
don’t stand a chance.
• It acts as an acid buffer to protect the
body from pathogens.
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Innate Immune System
Innate Immune System• Innate Immune System (IIS) comprises the cells and
mechanisms that defend the host from infection by other
organisms.
• IIS provides immediate defense against infection.
• The cells of the innate system recognize and respond
to pathogens in a generic way, but,
• IIS does not confer long-lasting or protective immunity to the
host.
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Ouch!
1. Inflammation
Acute inflammatory response is the body’s initial reaction to tissue
damage.
1. Wound occurs!
2. Wounded cells secrete chemicals that stimulate release of
histamine.
3. Histamine causes fluids to collect around an injury to dilute
toxins. This causes swelling.
4. The temperature of the tissues may rise, which can kill
temperature-sensitive microbes.
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2. Phagocytes
• Phagocytes are several types of
white blood cells (including
macrophages and neutrophils) that
seek and destroy invaders.
• Phagocytes are attracted by an
inflammatory response of damaged
cells.
3. Natural Killer Cells
• Are white blood cells
that recognize and
destroy virus-infected
cells or those that have
become cancerous
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Fever
• Fever is a defense mechanism that
can destroy many types of microbes.
• While high fevers can be dangerous,
some doctors recommend letting low
fevers run their course without
taking aspirin or ibuprofen.
Acquired (Adaptive) Immune System
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Acquired Immune System
• AIS gives us immunity to certain diseases.
• In the AIR, the immune system forms a
chemical “memory” of the invading microbe.
• If the microbe is encountered again, the body
reacts so quickly that few or no symptoms are
felt.
Some Vocabulary:
• Antigen (Pathogen) - any substance that
causes an immune system to produce
antibodies against it (e.g. bacteria, virus,
etc.).
• Antibody - a protein produced by the human
immune system to tag and destroy invasive
microbes.
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Acquired Immune System
• Lymphocytes - Main players of the acquired
immune system
− They are white blood cells that circulate in the
bloodstream and lymphatic system
− Two different types:
• T Cells (T Lymphocytes)
• B Cells (B Lymphocytes)
• T Cells - 3 types:
• Helper T Cells - detect the invading pathogen and trigger
production of killer T cells
• Killer T Cells - attack and kill invading pathogen and
infected body cells
• Suppressor T Cells - slow down and halt the immune
response when the threat has been handled
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Acquired Immune System
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Helper T Cells
• The Helper T-Cell is the key cell to signal an
immune response.
• If helper T-cells are disabled, the immune system
will not respond.
• AIDS – Helper T-Cells are disabled
• B Cells - a type of lymphocyte (white blood cell) that
monitor the blood and tissue fluids for antigens.
• Following the body’s first exposure to a pathogen,
the B Cells have a “memory” of the pathogen
• When they encounter a specific invading pathogen
again, they produce antibodies - proteins that bind
to specific invader (antigen)
• Killer T-Cells recognize the antibodies and will kill
the pathogen that is tagged with them.30
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Antibodies
• Antibodies released into the blood
stream will bind to the antigens
(pathogens) that they are specific for.
• Antibodies may disable some microbes,
or cause them to stick together
(agglutinate).
• They “tag” microbes so that the
microbes are quickly recognized by the
Killer t-cells.
1. Antigen invades body for the first time – you get sick
2. T-helper cells recognize threat and trigger the T-killer cells
3. B-cells produce antibodies that mark the antigen so that the t-killer cells
know which cells to attack.
4. Once the t-killer cells have the upper hand, the t-suppressor cells go into
action and begin shutting down the immune response.
5. Your immune system now has a “memory” of the antigen/pathogen. If
the pathogen ever invades again, your immune system is ready to defend
your body against it. When/if it does invade, you never know it
Let’s put it all together…
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Immunity
• After surviving infection by a pathogen, a person
often acquires immunity to future infections by the
same pathogen
• B and T cells become memory cells when exposed to
an infectious agent, allowing recognition and quick
action to destroy the invader before the illness begins
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Human Assist
Antibiotics and Vaccines
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Helping the immune system
• Medical science has
created to systems for
augmenting the human
immune system:
• Antibiotics
• Vaccines
How antibiotics work
• Antibiotics help destroy bacteria
(but not viruses).
• Antibiotics work in one of several
ways:
• Slowing bacteria reproduction.
• Interfering with bacterial cell wall
formation.
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Antibiotic myths
• Antibiotics are not antibodies.
• Antibiotics do not weaken our immune system. They
help it by weakening bacteria.
• Humans do not become “immune” to antibiotics.
Bacteria that resist antibiotics and are not completely
destroyed may multiply, producing more antibiotic-
resistant bacteria.
How vaccines work• Modern vaccines are created from killed bacteria or
viruses, or fragments of proteins from these
microbes.
• The proteins are recognized as antigens by our
immune systems. This causes a mild immune
response.
• Memory T-cells and B-cells remain ready to fight off
the illness if it is encountered again.
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How vaccines work
Vaccine myths
• The flu vaccine does not give you the flu. Some people get the
vaccine too late, or catch a cold and think they have the flu.
• Vaccines are not less effective than a “natural” infection with
the illness. The immunity is the same, and a mild response to a
vaccine is much less risky than a full-blown infection of
measles.
• There is NO link between vaccines and autism.
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Vitamin C for colds?
• Vitamin C is necessary for many
body functions.
• Absorption of Vitamin C increases
during illness. It also has a very
slight antihistamine effect.
• Vitamin C won’t cure a cold, but may
support some aspects of immune
response.
Zinc for colds?
• Some studies have shown that
moderate use of zinc
lozenges slightly decreases
the duration and severity of
colds.
• However, too much zinc can
suppress the immune system,
and can reach toxic levels.
Zinc nasal sprays can destroy
olfactory receptors.
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Vitamin D for colds?
• New research suggests that
Vitamin D plays a role in immune
response, and may be critical for
fighting off viruses.
• Vitamin D is fat-soluble and can
accumulate to toxic levels. A blood
test can determine if a person
needs to take Vitamin D.
Echinacea for colds?
• Echinacea is supposed to
“strengthen” the immune system.
• Studies in petri dishes showed
Echinacea stimulated white blood
cells to produce more virus-killing
peroxides, but controlled human
trials have not had consistent
results.