Download 39. Immune system

The Human Immune System
Video
What is the immune system?
• The body’s defense against disease causing
organisms, malfunctioning cells, and
foreign particles
The First Line of Defense
~Skin~
- The dead, outer
layer of skin, known
as the epidermis,
forms a shield
against invaders and
secretes chemicals
that kill potential
invaders
- You shed between
40 – 50 thousand
skin cells every day!
The First Line of Defense
~Mucus and Cilia~
- As you breathe in,
foreign particles and
bacteria bump into
mucus throughout
your respiratory
system and become
stuck
- Hair-like structures
called cilia sweep this
mucus into the throat
for coughing or
swallowing
Don’t swallowed bacteria have a
good chance of infecting you?
The First Line of Defense
~Saliva~
What’s the first thing you do when you cut
your finger?
- Saliva contains many
chemicals that break down
bacteria
- Thousands of different types
of bacteria can survive these
chemicals, however
The First Line of Defense
~Stomach Acid~
- Swallowed bacteria are
broken down by incredibly
strong acids in the stomach
that break down your food
- The stomach must produce a
coating of special mucus or
this acid would eat through
the stomach!
Think of the human body as a
hollow plastic tube…
The food is digested within the hole in the
tube, but it never actually enters into the
solid plastic material.
Tube inner surface
~Digestive System~
Tube outer surface
~Skin~
Plastic interior
~Body~
Escherichia coli
is common and plentiful in all of our
digestive tracts. Why are we all not
sick?
- These bacteria are
technically outside the
body and aid in digesting
material we cannot
- Only if E.Coli are
introduced in an unnatural
manner can they break
through the first line of
defense and harm us
The Second Line of Defense
~White Blood Cells~
- If invaders actually
get within the body,
then your white
blood cells (WBCs)
begin their attack
- WBCs normally
circulate throughout
the blood, but will
enter the body’s
tissues if invaders
are detected
Video
White Blood Cells
~Phagocytes~
• These white blood cells are
responsible for eating
foreign particles by
engulfing them
• Once engulfed, the
phagocyte breaks the
foreign particles apart in
organelles called ________
Lysosomes
Where could invaders
hide from phagocytes?
Viruses
Viruses enter body cells, hijack their organelles, and
turn the cell into a virus making-factory. The cell
will eventually burst, releasing thousands of viruses
to infect new cells.
Cell before infection…
…and after.
The Second Line of Defense
~Interferon~
- Virus-infected body
cells release
interferon when an
invasion occurs
- Interferon – chemical
that interferes with the
ability to viruses to
attack other body cells
What happens to already
infected cells?
White Blood Cells
~T-Cells~
• T-Cells, often called
“natural killer” cells,
recognize infected human
cells and cancer cells
• T-cells will attack these
infected cells, quickly kill
them, and then continue to
search for more cells to kill
The Second Line of Defense
~The Inflammatory Response~
- Injured body cells release
chemicals called
histamines, which begin
inflammatory response
- Capillaries dilate
- Pyrogens released, reach
hypothalamus, and
temperature rises
- Pain receptors activate
- WBCs flock to infected area
like sharks to blood
Two Divisions of the Immune
System
- The efforts of the WBCs known as
phagocytes and T-cells is called the cellmediated immune system.
- Protective factor = living cells
- Phagocytes – eat invaders
- T-cells – kill invaders
Two Divisions of the Immune
System
• The other half of the immune system is
called antibody-mediated immunity,
meaning that is controlled by antibodies
• This represents the third line of defense in
the immune system
The Third Line of Defense
~Antibodies~
- Most infections never make it
past the first and second levels
of defense
- Those that do trigger the
production and release of
antibodies
- Proteins that latch onto, damage,
clump, and slow foreign particles
- Each antibody binds only to one
specific binding site, known as an
antigen
Antibody Production
- WBCs gobble up invading
particles and break them up
- They show the particle
pieces to T-cells, who
identify the pieces and find
specific B-cells to help
- B-cells produce antibodies
that are equipped to find
that specific piece on a new
particle and attach
Video - 1:58
Immunity
- New particles take longer
to identify, and a person
remains ill until a new
antibody can be crafted
- Old particles are quickly
recognized, and a person
may never become ill from
that invader again. This
person is now immune.
What is immunity?
- Resistance to a disease causing organism or
harmful substance
- Two types
- Active Immunity
- Passive Immunity
Active Immunity
- You produce the antibodies
- Your body has been exposed to the antigen in
the past either through:
- Exposure to the actual disease causing antigen –
You fought it, you won, you remember it
- Planned exposure to a form of the antigen that has
been killed or weakened – You detected it,
eliminated it, and remember it
What is this second type of
exposure called?
Vaccine
• Antigens are deliberately introduced into the
immune system to produce immunity
• Because the bacteria has been killed or weakened,
minimal symptoms occur
• Have eradicated or severely limited several
diseases from the face of the Earth, such as polio
and smallpox
How long does active immunity
last?
• It depends on the antigen
• Some disease-causing
bacteria multiply into new
forms that our body doesn’t
recognize, requiring annual
vaccinations, like the flu
shot
• Booster shot - reminds the
immune system of the
antigen
• Others last for a lifetime,
such as chicken pox
Think the flu is no big deal?
- Think again…
- In 1918, a particularly
deadly strain of flu,
called the Spanish
Influenza, spread across
the globe
- It infected 20% of the
human population and
killed 5%, which came
out to be about 100
million people
Do we get all the possible
vaccines we can?
• Although the Center for
Disease Control (CDC)
recommends certain vaccines,
many individuals go without
them
• Those especially susceptible
include travelers and students
• Consider the vaccine for
meningitis, which is
recommended for all college
students and infects 3,000
people in the U.S., killing 300
annually
Link
Passive Immunity
• You don’t produce the
antibodies
– A mother will pass
immunities on to her baby
during pregnancy - through
what organ? Placenta
– These antibodies will
protect the baby for a short
period of time following
birth while its immune
system develops. What
endocrine gland is
responsible for this? Thymus
– Lasts until antibodies die
Why doesn’t the mother just
pass on the WBCs that
“remember” the antigens?
Immune Disorders
~Allergies~
- Immune system mistakenly
recognizes harmless foreign
particles as serious threats
- Launches immune response,
which causes sneezing, runny
nose, and watery eyes
- Anti-histamines block effect of
histamines and bring relief to
allergy sufferers
Aquired Immune Deficiency Syndrome
• Caused by the Human
Immunodeficiency Virus
• Discovered in 1983
• Specifically targets and kills
T-cells
• Because normal body cells are
unaffected, immune response
is not launched
AIDS
~The Modern Plague~
- The HIV virus doesn’t kill
you – it cripples your
immune system
- With your immune system
shut down, common diseases
that your immune system
normally could defeat
become life-threatening
- Can show no effects for
several months all the way
up to 10 years
AIDS
~The Silent Spread~
• Transmitted
by sexual
contact, blood
transfusions,
contaminated
needles
• As of 2007, it
affects an
estimated 33.2
million people
• You wake up one morning with a stuffy
nose, slight fever, and fatigue. Do you have
a cold or the flu? Or are they the same?
• Should you go to your doctor for an
antibiotic? Why or why not?
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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
Virus vs. Bacteria
• Colds and influenza
are caused by viruses.
• Viruses are which is a
non-living particle that
contains genetic
material, and hijacks
your cells to
reproduce.
• Viruses cannot be
“killed” with
Rhinovirus
Influenza
virus
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
because these
substances target key
E. coli
Streptococcus
Body Defenses
• Viruses and bacteria are everywhere. Some
of them want to invade your body. How
does your body defend itself against viruses
and bacteria?
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Defense Against Disease
Nonspecific External Barriers
skin, mucous membranes
If these barriers are penetrated,
the body responds with
Innate Immune Response
phagocytic and natural killer cells,
inflammation, fever
If the innate immune response is insufficient,
the body responds with
Adaptive Immune Response
cell-mediated immunity, humoral immunity
First line of defense
• Non-specific defenses are designed to
prevent infections by viruses and bacteria.
These include:
– Intact skin
– Mucus and Cilia
– Phagocytes
Role of 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.
Role of mucus and cilia
• Mucus contains lysozymes,
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.
Role of phagocytes
• Phagocytes are several types
of white blood cells
(including macrophages and
neutrophils) that seek and
destroy invaders. Some also
destroy damaged body cells.
• Phagocytes are attracted by
an inflammatory response of
damaged cells.
Role of inflammation
• Inflammation is signaled by mast cells,
which release histamine.
• Histamine causes fluids to collect around
an injury to dilute toxins. This causes
swelling.
• The temperature of the tissues may rise,
which can kill temperature-sensitive
microbes.
Role of fever
• Fever is a defense mechanism that can
destroy many types of microbes.
• Fever also helps fight viral infections by
increasing interferon production.
• While high fevers can be dangerous, some
doctors recommend letting low fevers run
their course without taking aspirin or
ibuprofen.
Ouch!
Fever is caused by:
1. Toxins on the
surface of viruses.
2. Release of
histamines by
damaged cells.
3. Your own body’s
accumulated toxins.
4. Your body’s
pyrogens signaling
the hypothalamus.
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Based on what you know about non-specific
defenses, what’s the best way to treat a cut in
your skin?
1. Leave it exposed to
open air.
2. Wash it, and cover
it with a clean
bandage.
3. Rub it with dirt.
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• Why aren’t non-specific defenses enough?
Why do we also need specific defenses?
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Specific defenses
• Specific defenses are those that give us
immunity to certain diseases.
• In specific defenses, 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.
Major players
• The major players in the immune system
include:
–
–
–
–
Macrophage
T cells (helper, cytotoxic, memory)
B cells (plasma, memory)
Antibodies
Some vocabulary:
• Antibody: a protein produced by the human
immune system to tag and destroy invasive
microbes.
• Antibiotic: various chemicals produced by
certain soil microbes that are toxic to many
bacteria. Some we use as medicines.
• Antigen: any protein that our immune system
uses to recognize “self” vs. “not self.”
Antibodies
• Antibodies are
assembled out of
protein chains.
• There are many
different chains that
the immune system
assembles in
different ways to
make different
antibodies.
Antibodies as Receptors
• Antibodies can
attach to B cells,
and serve to
recognize foreign
antigens.
Antigens as Effectors
• Free antibodies
can bind to
antigens, which
“tags” the antigen
for the immune
system to attack
and destroy.
Antigen recognition
• Cells of the immune system are “trained” to
recognize “self” proteins vs. “not self”
proteins.
• If an antigen (“not self”) protein is
encountered by a macrophage, it will bring the
protein to a helper T-cell for identification.
• If the helper T-cell recognizes the protein as
“not self,” it will launch an immune response.
Helper T cells
• Helper T-cells have receptors for
recognizing antigens. If they are presented
with an antigen, they release cytokines to
stimulate B-cell division.
• The helper T-cell is the key cell to signal
an immune response. If helper T-cells are
disabled, as they are in people with AIDS,
the immune system will not respond.
B cells
• B-cells in general produce antibodies.
Those with antibodies that bind with the
invader’s antigen are stimulated to
reproduce rapidly.
• B-cells differentiate into either plasma
cells or memory B-cells. Plasma cells
rapidly produce antibodies. Memory cells
retain the “memory” of the invader and
remain ready to divide rapidly if an
invasion occurs again.
Clonal Selection
Role of antibodies
• Antibodies released into the blood stream
will bind to the antigens 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 various white
blood cells.
“Killer” T cells
• While B-cells divide and differentiate,
so do T-cells.
• Some T-cells become cytotoxic, or
“killer” T-cells. These T-cells seek out
and destroy any antigens in the system,
and destroy microbes “tagged” by
antibodies.
• Some cytotoxic T-cells can recognize
and destroy cancer cells.
Calling a halt
• When the invader is destroyed, the helper
T-cell calls a halt to the immune response.
• Memory T-cells are formed, which can
quickly divide and produce cytotoxic Tcells to quickly fight off the invader if it is
encountered again in the future.
A foreign protein that enters the
body is an:
1.
2.
3.
4.
antibiotic.
antigen.
antibody.
anti-inflammatory.
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The specific immune response is
triggered when:
1. A macrophage
delivers an antigen
to a T-helper cell.
2. Plasma cells begin
making antibodies.
3. Pyrogen stimulates
a fever.
4. Clonal selection of
B-cells occurs.
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• Why is it important for the immune system
to have a way of stopping the immune
response? Why not just keep going and
fight off everything as it comes?
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Human Assist
Helping the immune system
• Medical science has
created to systems
for augmenting the
human immune
system:
– Antibiotics (NOT
the same as
antibodies)
– 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.
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.
Vaccine history
• Variolation: The
deliberate inoculation
of people with
secretions from
smallpox (Variola)
sores, by inhaling the
dried secretions or
rubbing them on
broken skin. Used for
centuries in Asia and
Vaccine history
• Vaccination: (From vacca,
Latin for cow.) Invented by
Edward Jenner in 1796.
Jenner knew that dairy maids
who had contracted cowpox
never got smallpox. He
inoculated a boy with
secretions from cowpox
sores, and showed the boy
was immune to smallpox.
Not that everyone accepted the process.
Cartoons like this created widespread fear
of the “cow pock” vaccine.
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.
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.
• The proposed link between vaccines and
autism turns out to have far less experimental
True or false: Antibiotics weaken the immune
system because your body doesn’t learn to make
enough antibodies.
1. True. Antibiotics
are a type of
antibody.
2. False. Antibiotics
are not antibodies.
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True or false: Vaccines weaken the immune system
because the body doesn’t learn to defend itself
without help.
1. True. The immune
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system needs to
exercise itself or it
won’t get strong.
2. False. Vaccination
causes the body to
learn to defend
itself.
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Vaccines stimulate the production
of:
1.
2.
3.
4.
Antibodies.
Helper T-cells.
Antigens.
Memory cells.
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• Why will antibiotics work against bacteria
but not viruses?
• Why don’t antibiotics kill your own cells?
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Immune system
challenges
But I caught a cold... again!
• Because there are over 100 different
known rhinoviruses, it’s possible to catch
colds again and again.
• In addition, cold viruses can mutate
quickly. No sooner do we have immunity
to one form than along comes another.
How did I get this cold?
• To catch a cold, a rhinovirus must reach the
mucus membranes of your upper respiratory
system.
• Your hands pick up rhinoviruses from surfaces.
Every time you touch your eyes or nose, or eat
something with your hands, the viruses get a
free ride. Like Mom said, wash your hands!
• Viruses may also ride on re-circulated air, or
reach you if someone sneezes right at you.
Cold myths
• Colds and “the flu” are different illnesses. Not every respiratory
infection is “the flu.”
• Colds are not caused by getting chilled. This belief comes from
medical ideas of prior centuries, when it was believed that illness
was caused by an imbalance of “humors,” and that a person with a
cold actually had too much “coldness.”
• “Feed a cold, starve a fever” also comes from prior centuries, when
it was thought that people with a cold had too much “cold” and
“moisture” in their bodies, and needed food to increase heat, while
people with fever had too much “dryness” and “heat,” so needed less
food to cool them down.
Cold vs. “Flu” (influenza)
Symptoms
Cold
Flu
Fever
rare
characteristic
Headache
mild (sinus)
strong
Aches & Pains
slight
usual, strong
Fatigue
mild
2-3 weeks
Exhaustion
never
early, profound
Stuffy nose
usual
sometimes
Sneezing
usual
sometimes
Sore throat
common
sometimes
Chest discomfort
mild
common, strong
Stomach flu?
• Influenza is a respiratory virus. Strictly
speaking, there is no stomach flu.
• There are, however, viruses that attack the
digestive system. Norovirus and rotavirus
cause the nausea, vomiting, and diarrhea that
many people call “stomach flu.”If left
untreated, the rapid dehydration these viruses
cause can be fatal.
• Bacterial food poisoning can also cause fastonset vomiting and diarrhea.
Echinacea for colds?
• Echinacea is
supposed to
“strengthen” the
immune system.
• Studies in petri dishes
showed Echinacea
stimulated white
blood cells to
produce more viruskilling peroxides, but
Vitamin C for colds?
• Vitamin C is necessary
for making collagen, and
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
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.
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.
Evolution of the flu
• Flu viruses also mutate quickly.
• The same form of the flu may have the
ability to infect several different
vertebrate animals.
• Different forms may hybridize their
genetic material, causing new strains to
develop in a single generation.
New Flu
Flu Pandemic
• The deadly 1918 flu
pandemic has been
recently identified as
an avian flu. Unlike
common flu, it killed
mostly young,
healthy people.
• The recent H1N1
flu, mostly a swine
flu, had many avian
Allergies
• Allergies are an immune system
reaction to harmless antigens.
• Some, such as pollen, may get in
through the respiratory system.
Fragments of food proteins may get
through the digestive system.
• The next time these proteins are
encountered, the immune system
attacks them.
Achoo!
• Pollen is a harmless
protein, yet we can
become allergic to it.
• Most of the
symptoms are
caused by histamines
released by mast
cells. That is why
antihistamines are
used to treat
Autoimmune disorders
• Autoimmune disorders occur when the
immune system fails to recognize a
protein as “self” and launches an attack.
• Multiple sclerosis, lupus, and rheumatoid
arthritis are examples. None of these can
be cured, but drugs can help slow the
progress of these diseases.
Cancer
• Cancer occurs when the mechanisms that
control cell division fail, and body cells divide
out of control.
• Cytotoxic T-cells can recognize and destroy
these cells. But if division is too rapid, the Tcells cannot keep up.
• Some cancer research involves assisting
cytotoxic T-cells in recognizing and destroying
cancer cells.
AIDS
• AIDS (Acquired Immune Deficiency
Syndrome) is caused by an infection by the
HIV (Human Immunodeficiency Virus), which
attacks and destroys T-helper cells. Because it
attacks the immune system directly, finding a
vaccine has been difficult.
• Some drugs can slow down HIV reproduction,
but no cure exists yet. Prevention is still the
best “cure.”
AIDS
The HIV virus fools helper
T-cells into thinking its
proteins are “self,” and so
is able to infect the cells
that trigger specific
immunity.
The virus forces Tcells to make more
viruses, killing the
T-cells when the
new viruses burst
AIDS Prevention
• HIV is a fragile virus that cannot live
outside the human body for more than a few
minutes.
• Preventing HIV spread comes down to
preventing exposure to body fluids of an
infected person.
SCID
• Severe Combined Immune Deficiency is a
genetic condition in which one or more genes
for proteins crucial for the immune system are
defective. Children born with SCID have no
immune system.
• Gene therapy has been used to inject a good
copy of the defective gene into blood cells or
bone marrow cells. In several cases this has
been effective, though it is still experimental.
Which cell does HIV attack?
1.
2.
3.
4.
Macrophage.
Red blood cell.
Helper T-cell.
B-Memory cell.
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If AIDS attacks specific immune defense, would a
person with AIDS have a fever if they catch the flu?
1. Yes. Fever is a nonspecific response.
2. No. The entire
immune system has
been compromised.
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For some people, pollen allergies grow
worse every year. Why?
1. More pollen is
produced every
year.
2. Memory cells cause
a stronger reaction.
3. Pollen evolves
stronger toxins.
4. Suppressor T-cells
become more active
with time.
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• Discuss the best ways to prevent yourself
from catching colds and influenza.
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