Download 2-2 immunity F11

Bio 11:
The Body’s Defenses
Problems with nonspecific
immunity:
Sometimes too many invaders will enter
body for phagocytes, NK cells, etc to
eliminate quickly enough to prevent
infection.
Nonspecific defenses spread their efforts
– not focused
Specific Defenses
Need another defense system
to target those specific
particularly nasty invaders.
Two ‘teams’ of WBCs act in
the specific defenses

B cells
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develop in the
Bone marrow
B cells
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T cells
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Fighting the Invaders
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become
specialized in the
Thymus
T cells
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Different roles in
the immune
response
Special weapon: antibodies
Target: bacteria and viruses

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Helper T cells
Cytotoxic (or “killer”) T cells
Memory cells
Target: pathogens inside cells, some
cancer cells and transplanted tissue
Copyright 2009, John Wiley &
Sons, Inc.
B-cells
The specific defenses

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A large number of cells work together to
respond to a specific microbe or foreign
invader.
X
Defenses
T-cells
Antibody-mediated
response
Cell mediated
response
Digests Pathogen
• Displays its Proteins
Two properties
 Specificity for a particular foreign (non-self)
molecule

Memory for previously encountered invaders

Recognizes
Display
The immune system can react more promptly to a
second exposure to infection.
Secretes antibodies
Kills Infected Cells
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APC
Recognizing the invaders

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Antigen Presenting
Cells (APCs)
Seek out invaders
and relays
information about
them to other
defense cells
Helper
T cell
Helper T Cells Use
Information from APCs to
Initiate Specific Attacks
Each helper T cell recognizes a
different antigen. Over a billion
different types of T Cell receptors in
our bodies!
(Antigens = any foreign particles)
Antigens = any foreign particles
Scouts
Cytotoxic T Cells
T cell training
The thymus “trains” T Cells
before they mature &
communicate with APCs
Makes sure T Cells:
1) Recognize HLA markers
2) Won’t attack cells with
friendly/self markers
Active Cytotoxic T Cells kill
infected cells
Stimulated by
Helper T Cells
Attack infected
body cells
Cytotoxic (killer) T cells also
kill cells infected with viruses
http://www.youtube.com/watch?v=1tBOmG0QMbA
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T-cells
T cell defenses
Cell mediated
response
Digests Pathogen
• Displays its Proteins
Activated B Cells
Divide Into Plasma
Cells & Produce
Antibodies
1st step
Like Special Weapons
Developers
Activates
Plasma cells
2nd
step
Kills Infected
Cells
Antibodies
Antibodies eliminate specific
invaders (antigens)


Y-shaped proteins
that bind a particular
foreign molecule
(antigen)
Specific
Memory T Cells & B Cells respond
if a familiar invader returns
Familiar Invader
Plasma cell
Immediately
divide into active
cytotoxic T cells
Immediately
divide into active
helper T cells
Immediately divide
into plasma cells
Specific immunity: Abs
1:01
http://www.youtube.com/watch?v=Ys_V6FcYD5I&NR=1
APCs, T Cells, and B Cells Hang
Out in Specific Areas of the Body
70% of Immune System
Tissue in Body = MALT!
Definitions

Antigens
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Mucosa Associated Lymphoid
Tissue
Found in gut, bronchi, nose,
bladder, vagina, etc.
Also find immune cells in the
lymph nodes and spleen


Are foreign substances that trigger an
immune response
Most are pathogens
Antibodies

Are proteins made by our body that
attack one particular foreign invader (or
antigen)
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The immune response
What is the response of B
cells and T cells?

B cells secrete antibodies that
inactivate foreign invaders
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Sends
signals
lymph, attacking infected body cells
Antibodymediated
The immune response

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Cell-mediated immunity
Specificity: immune cells
recognize self vs non-self
The specific defenses
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Antibody-mediated immunity
T cells circulate in the blood and
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Two properties
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Specificity for foreign molecules (antigens)
Memory for previously encountered “invaders”

The immune system can react more promptly to a
second exposure to infection.
Self-markers located
on cell surfaces
A large number of B and T cells that work together
to respond to a specific microbe or foreign invader.
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unique to each person
Help T cells distinguish
foreign from self
T cells do not react to
self-markers
 Self-tolerance
HLA and MHC = Protein markers
on cell surfaces
Key to Immunity: Recognizing self vs. non-self
Graph or organ rejection
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Immune system recognizes the
self proteins in the transplanted
organ as foreign and mounts an
immune response
Tissue typing
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Match MHC proteins of donor and
recipient
Why do organ transplant
recipients receive
immunosuppressive drugs?
Autoimmune diseases
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Due to loss of self-tolerance
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The immune system attacks the person’s
own tissues
Examples
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Type 1 diabetes - T cells attack the insulinproducing pancreatic beta cells
Multiple sclerosis (MS) - T cells attack
myelin sheaths around axons of neurons
Copyright 2009, John Wiley &
Sons, Inc.
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Memory:
How vaccinations work
Memory:
How vaccinations work
Vaccine is injected → body mounts an
immune response
Activated B cells
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Vaccines trigger the
immune reaction,
stimulating the body
to defend itself and
create memory B
and T cells.
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Plasma cells that secrete antibodies
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Memory B cells that remain in the
body and produce antibodies if that
antigen enters the body again
Activated T cells
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Cytotoxic T cells that attack the antigen
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Memory T cells that respond quickly
to a second exposure to the antigen
Allergies result from inappropriate
immune responses
Immunologic memory
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The 1st exposure to an antigen
takes several days to produce
immune cells
peak levels occur at 1-2 weeks
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1st Exposure to Allergen:
Plasma cells make antibodies
which attach to mast cells
(another white blood cell)
2nd Exposure to Allergen:
Mast cells with antibodies are
stimulated, release histamines
The 2nd exposure elicits a
faster, stronger response
Due to the presence of
thousands of memory B and T
cells
Inflammation
Copyright 2009, John Wiley &
Sons, Inc.
How does the body respond to
a viral infection?
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The common cold
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A contagious viral
disease of the upper
respiratory track
Primarily caused by
rhinoviruses
The most common
infectious disease in
humans
Specific immune responses
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The host's immune
system effectively deals
with the cold virus.
The B cells begin
producing antibodies
that bind to the virus and
prevent it from infecting
cells.
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Specific immune responses
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Infected cells display viral
antigens on their surface
If a cytotoxic T cell
recognizes a viral fragment
there, it will destroy the
infected cell
How does the body respond to
a viral infection?
External barriers
Skin, mucous membranes, secretions
The first responders
Specific responses
B cells produce antibodies
to the virus
NK cells
Interferon
Helper T cells
Rhinovirus
Cytotoxic T cells attack
virus-infected cells
Inflammation
HIV Infects Helper T Cells
Helper T Cell
Why is HIV so lethal?
X
Replicated HIV
Budding Off From Cell
HIV infects and kills helper
T Cells
How does this impact the
body’s immune responses?
X
X
Antibodymediated
X
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