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Immune System
Professor Andrea Garrison
Biology 11
Illustrations ©2010 Pearson Education, Inc.
Immune System
• Function = defend against infectious disease
and other “invaders” that can cause harm
– Includes pathogens
• Viruses and micro-organisms with potential to cause
disease
– Includes toxins and other substances that can
harm us
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Immune System
Involves Three Lines of Defense
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Immune System
Involves Three Lines of Defense
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Immune System
Involves Three Lines of Defense
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Immune System
• Innate Defenses
• Adaptive Defenses
– Also called Non-Specific
Defenses
– Respond to any invader
– Also called Specific
Defenses
– Respond to very specific
types of invaders
immune system after
exposure
• e.g., polio virus
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Immune System
Involves Three Lines of Defense
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Innate (Non-Specific) Defenses
• Operate without previous exposure to
pathogen
– External defenses (barriers to invasion)
• Prevent pathogens from getting into body
• Work for most pathogens in most situations
– Internal defenses
• Destroy pathogens that get through barriers
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External Innate Defenses
• Skin
• Mucous membranes
– Mucus contains lysozyme
• Breaks down bacterial walls
• Tears, saliva, sweat contain
lysozyme
• Gastric fluid contains
lysozyme
• Microbes
– Outcompete pathogens
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When External Innate Defenses Fail. . .
Internal Innate Defenses
• White Blood Cells
– Phagocytic cells
• Engulf foreign cells or
molecules/debris from dead
cells
• Alert adaptive defense system
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Internal Innate Defenses
• White Blood Cells
– Natural killer cells
• Recognize virus-infected &
cancerous cells
• Release chemicals to kill them
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Internal Innate Defenses
• Defensive proteins
– Interferon
• Produced by virus-infected
cells
• Bind to receptors on healthy
cells
• Trigger production of antiviral
proteins by healthy cells
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Internal Innate Defenses
• Defensive proteins
– Complement proteins
• Attach microbes
– Coat surface making job
easier for phagocytes
– Tear holes in microbe
membranes
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Internal Innate Defenses
• Inflammatory response
– We see it all the time
– Don’t recognize its value
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Inflammatory Response
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Inflammatory Response
Swelling, redness, warmth
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Inflammatory Response
Swelling, redness, warmth
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Fever
• May occur with inflammation or an infectious
disease
• Pyrogens
– Released by some bacteria
– Released by white blood cells in response to
infection
– Released by severely damaged cells
– Brain responds by creating environment too hot
for viruses and bacteria to reproduce well
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Immune System
Involves Three Lines of Defense
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Adaptive (Specific) Defenses
• Respond to specific types of invaders after
exposure
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Adaptive Defenses
• All cells and molecules have markers allowing
them to be recognized
• “Self” markers are called MHC markers
• “Non-self” markers are called antigens
– Your MHC markers are antigens to anyone else
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Adaptive Defenses
• Response to antigens
– Lymphocytes (type of white blood cells)
• B cells complete development in bone marrow
• T cells complete development in thymus gland
– Travel to lymph nodes and other lymphatic organs
– Also reside in blood
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Adaptive Defenses
• Response to antigens
– B cells and T cells have antigen receptors in their
cell membranes
• Bind to specific antigen based on shape
– B cells and T cells have receptors for almost every
possible antigen
• Lie in wait for that antigen to invade body
• Only few cells with each receptor shape
• Most will never be used
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Adaptive Defenses
• Humoral Immune
Response
• Cell-mediated Immune
Response
– Also called antibodymediated response
– B cells
– Protect against invaders
not yet in cells
• In blood
• In tissue outside cells
– T cells
• Helper T cells
• Cytotoxic T cells
– Protect against body’s
own cells that pose
danger
• Invaded by pathogen
• Cancerous
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Adaptive Defenses
• Humoral Immune
Response
• Cell-mediated Immune
Response
– Primary immune
response
– Primary immune
response
• Gets you well
• Gets you well
– Secondary immune
response
– Secondary immune
response
• Keeps you from getting
same disease twice
• Keeps you from getting
same disease twice
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Humoral Immune Response
• B cell response to
antigens
– B cells with correct
receptor for antigen will
make an antibody with
the complementary
shape to the antigen
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Humoral Immune Response
• Antibody binds to
antigens
– Antibody-antigen
complex triggers
destruction
• Marks invader for
phagocytes
• Physically blocks its
entrance to cells
• Triggers complement
proteins
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Building Humoral Immune Response
• Initially only a few of each type of B cells
– A few B cells produce antibodies to invader
• Once the B cells w/correct antibody are found
they divide rapidly
– Some short-lived cells produce large numbers of
antibodies to fight invader – PRIMARY RESPONSE
– Some cells become memory B cells to protect
against invasion a second time – SECONDARY
RESPONSE
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Initially only a few of each type of B cells, so
very few antibodies
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Once the B cells w/correct antibody are
found they divide rapidly
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Antibody producing effector B cells
Immune System
Memory B cells protect against
later invasion
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Humoral Immune Response
• Primary response
– Takes 10-14 days to build response
– Short-lived effector B cells produce antibodies
– Antibodies destroy invader free in bloodstream or
lymphatic system
• Secondary response
– Memory B cells are produced that live a long time
and fight infection immediately the next time you
are invaded by same invader
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Cell-Mediated Immune Response
• Body cell response to
invasion
– Cell binds antigen to
MHC marker and
displays complex on cell
membrane
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Cell-Mediated Immune Response
• Cytotoxic T cell
response to MHCantigen display
– Cytotoxic T cells with
correct receptor for
antigen will bind to
infected cells displaying
the MHC-antigen
complex
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Cell-Mediated Immune Response
• Cytotoxic T cell
response to MHCantigen display
– Cytotoxic T cells with
correct receptor for
antigen will bind to
infected cells displaying
the MHC-antigen
complex
– Cytotoxic T cells kill
infected cell
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Building Cell-Mediated Immune
Response
• Antigen presented by phagocyte triggers two types
of T cells (with correct receptor) to divide and fight
invader –PRIMARY RESPONSE
– Cytotoxic T cells
• Kill infected cells
– Helper T cells
• Assist cytotoxic T cells and B cells
• Some cells become memory T cells to protect against
invasion a second time – SECONDARY RESPONSE
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Cell-Mediated Immune Response
• Primary response
– Takes 10-14 days to build response
– Cytotoxic T cells destroy infected cells
• Secondary response
– Memory T cells are produced that live a long time
and fight infection immediately the next time you
are invaded by same invader
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Function of Helper T Cell
• Helper T cells critical in adaptive immune
response
• Helper T cells bind to antigen presented by
phagocyte
• Helper T cells stimulate division of correct B
cells and cytotoxic T cells, as well as memory B
cells and memory T cells
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Activation of Helper T Cell
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Activation of Helper T Cell
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Activation of Helper T Cell
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Activation of Helper T Cell
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Role of Activated Helper T Cell
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Adaptive Immune Response – Primary
and Secondary
Cytotoxic T cells
Memory B cells act fast if another
invasion
Memory T cells act fast if another
invasion
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Adaptive Immune Response
Which type of lymphocyte is attacked by
HIV?
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Adaptive Immune Response
Which type of lymphocyte is attacked by
HIV?
Helper T cells!!!
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Adaptive Immune Response
Which type of lymphocyte is attacked by
HIV?
Helper T cells!!!
Both the humoral immune response and
the cell-mediated immune response are
destroyed!
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Using Our Knowledge of the Immune
System
• Vaccinations
– Use harmless “dead” or weakened pathogen
– Stimulate primary response
• Body may act “sick”—no pathogen
– Stimulate secondary response
– May require booster
• Increase antibody levels sufficiently to fight invader
quickly
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Immune System Disorders
• Allergies
– Immune reaction to harmless substance
– First exposure develops antibodies
• Bind to body’s mast cells
– Produce histamines, minor response
– Second exposure triggers large number of
antibodies
• Histamines released
– Blood vessels dilate, leak
» Itchy eyes, tears, runny nose
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Immune System Disorders
• Autoimmune diseases
– Body’s cells don’t recognize “self” markers
•
•
•
•
Rheumatoid arthritis
Lupus
Insulin dependent diabetes
Multiple sclerosis
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Immune System Disorders
• Immunodeficiency diseases
– Severe Combined Immunodeficiency (SCID)
• Very low levels of B and T cells
• Require protection or bone marrow transplants
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Immune System Disorders
• Immunodeficiency diseases
– Severe Combined Immunodeficiency (SCID)
• Very low levels of B and T cells
• Require protection or bone marrow transplants
– Acquired Immunodeficiency Syndrome (AIDS)
•
•
•
•
Caused by HIV
Has killed >30 million people worldwide
Destroys helper T cells
Susceptible to opportunistic pathogens
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Immune System Disorders
• HIV
– Patients susceptible to diseases healthy people
easily fight
– Syndrome
• Lots of different diseases can attack patient
– Symptoms
• Little to none at first—flu-like, night sweats, fever
• Long latent period
• Opportunistic infections
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Immune System Disorders
• HIV
– Disease of blood
– Transmission
• Body fluids
• Sex, illegal drug use (hypodermic needles), mother to
child, very occasionally blood transfusion
• Virus dies quickly upon contact with air
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Immune System Disorders
• HIV
– Protection
• Don’t do drugs
• Don’t have multiple sex partners
– Monogamous relationship
– Test if either partner previously sexually active
• Use of latex condoms reduces risk (not 100%)
• Infected pregnant women should get treatment
• Infected mothers should not breast feed
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