Download antigens????

Function of the Immune System
 Prevent pathogens from entering
 Eliminate pathogens from body
 Provide memory against future infections from same
pathogen
– Pathogen = agent that causes disease
© 2012 Pearson Education, Inc.
Figure 42.2 Blood Cells
2 Divisions of Immune System
 INNATE (Non-specific)
– 1st line of defense; general response
– Quick to respond
– Prevent than eliminate
– Same response whether or not pathogen encountered
before
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2 Divisions of Immune System
 ADAPTIVE (Specific)
– Recognizes specific pathogens
– Slower to respond (1st time)
– Responsible for immune system memory
– Previous exposure to pathogen enhances immune response
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INNATE IMMUNITY
© 2012 Pearson Education, Inc.
Figure 24.1A
Innate immunity (24.1–3)
The response is the same whether
or not the pathogen has been
previously encountered
External
barriers (24.1)
Internal
defenses (24.1–2)
• Skin/
exoskeleton
• Acidic
environment
• Secretions
• Mucous
membranes
• Hairs
• Cilia
• Phagocytic cells
• NK cells
• Defensive
proteins
• Inflammatory
response (24.2)
Adaptive immunity
(24.4–15)
Found only in
vertebrates; previous
exposure to the
pathogen enhances the
immune response
• Antibodies (24.8–10)
• Lymphocytes
(24.11–13)
The lymphatic system (24.3)
Some Components of Innate immunity
 Phagocytic cells
– Neutrophils and macrophages,
– large cells that wander through the interstitial fluid and blood
– Destroy bacteria and virally-infected cells
 natural killer cells that attack cancer cells and virusinfected cells
 complement system, a group of proteins that
recruit other immune responses
 Inflammation and Histamine
© 2012 Pearson Education, Inc.
Figure 24.2_1
Pin
Skin surface
Bacteria
Signaling
molecules
White
blood cell
Blood vessel
1
Tissue injury; signaling
molecules, such as histamine,
are released.
Figure 24.2_2
Swelling
Blood clot
Phagocytes and
fluid move
into the area
2 Dilation and increased leakiness
of local blood vessels;
phagocytes migrate to the area.
Figure 24.2_3
Phagocytes
3
Phagocytes (macrophages and
neutrophils) consume bacteria
and cellular debris; the tissue
heals.
Lymphatic System Function
 Return tissue fluid back to CV system
 Fight infection
– As lymph circulates through lymphatic organs it collects
pathogens
– transports them to lymphatic organs
– Here, macrophages engulf the invaders and
– lymphocytes may mount an adaptive immune response.
© 2012 Pearson Education, Inc.
Figure 24.3
Organs
Adenoid
Tonsils
Lymphatic ducts
that drain into veins
Lymph node
Lymph nodes
Masses of
lymphocytes and
macrophages
Thymus
Lymphatic
vessels
Valve
Lymphatic vessel
Spleen
Blood capillary
Tissue cells
Interstitial fluid
Appendix
Bone
marrow
Lymphatic
capillary
ADAPTIVE IMMUNITY
© 2012 Pearson Education, Inc.
24.4 The adaptive immune response counters
specific invaders
 Our immune system responds to foreign molecules called
antigens
 Antigens
– are molecules that elicit the adaptive immune response,
– Example: proteins or large polysaccharides on the surfaces of
viruses or foreign cells
 The adaptive immune system
– reacts to specific pathogens
– “remembers” an invader.
© 2012 Pearson Education, Inc.
24.5 Lymphocytes mount a dual defense
 Lymphocytes
– are responsible for adaptive immunity, and
– originate from stem cells in the bone marrow.
– B lymphocytes or B cells continue developing in bone marrow.
– T lymphocytes or T cells develop further in the thymus.
© 2012 Pearson Education, Inc.
Figure 24.5A
Stem cell
Bone
marrow
Via
blood
Immature lymphocytes
Thymus
Antigen
receptors
B cell
Via
blood
T cell
Final maturation
of B and T cells in a
lymphatic organ
Lymph
nodes,
spleen, and
other
lymphatic
organs
Humoral
immune response
Cell-mediated
immune response
24.5 Lymphocytes mount a dual defense
 B cells
– participate in the humoral immune response
– Acts on extracellular pathogens (pathogens in body fluids)
Attack pathogens OUTSIDE body cells!!!!
– secrete antibodies into the blood and lymph to mark pathogen for
destruction
 T cells
– participate in the cell-mediated immune response,
– attack cells infected with bacteria or viruses; cancerous cells
– promote phagocytosis by other white blood cells and stimulating B
cells to produce antibodies.
–
Help bridge B-cell and Innate immune responses
© 2012 Pearson Education, Inc.
Figure 42.6 The Specific Immune System
24.5 Lymphocytes mount a dual defense
 Millions of distinct B and T cells
– each with different antigen receptors, capable of binding
one specific type of antigen,
– Antibodies = antigen receptors of B cells
– T cell receptors = antigen receptors of T cells
 Antigenic determinants are specific regions on an
antigen where antibodies bind.
– An antigen usually has several different determinants.
© 2012 Pearson Education, Inc.
Figure 42.9 The Structure of An Immunoglobulin
Figure 42.11 A T Cell Receptor
Key Point to
Remember:
Each B and T cell
displays unique
set of antigen
receptors on cell
surface
Each receptor can
specifically bind to
a unique antigen
Stem cell
Bone
marrow
Via
blood
Immature lymphocytes
Thymus
Antigen
receptors
B cell
Via
blood
T cell
Final maturation
of B and T cells in a
lymphatic organ
Lymph
nodes,
spleen, and
other
lymphatic
organs
Humoral
immune response
Cell-mediated
immune response
Development of Immune System Memory by
CLONAL SELECTION
Legal Disclaimer:
Clonal selection occurs in a similar manner for
T cell-mediated immune memory
(the following events are fictional - any resemblance to
Historical characters is just coincidence - no B cells or
Pathogens were actually harmed in the making of this animation.
© 2012 Pearson Education, Inc.
Figure 42.7 Clonal Selection in B Cells
CLONAL SELECTION
Primary immune response
1
B cells with
different
antigen
receptors
Antigen
receptor
on the cell
surface
Every B cell displays unique
antigen receptor on surface
CLONAL SELECTION
Primary immune response
1
B cells with
different
antigen
receptors
Antigen
receptor
on the cell
surface
2
Antigen
molecules
Antigen only binds to B cell with
complementary receptor
CLONAL SELECTION
Primary immune response
1
B cells with
different
antigen
receptors
Antigen
receptor
on the cell
surface
2
Antigen
molecules
3
First exposure
to the antigen
I WON THE
ANTIGEN
LOTTERY!!
The selected B cell now divides
rapidly!!!
Figure 24.7A_s4
Primary immune response
1
B cells with
different
antigen
receptors
Antigen
receptor
on the cell
surface
2
Antigen
molecules
3
First exposure
to the antigen
We’ll
hang out
And wait for the
next invasion
We’ll mark the
Pathogen for
Elimination!!
Antibody
molecules
4
Plasma cells - secrete antibodies
5
Memory cells
Figure 24.7A_s5
Secondary immune response
Alright boys, the pathogen is
Back!! Looks like we’re in
Charge of the second offensive Get ready to divide!!
Antigen
molecules
Second
exposure
to the same
antigen
Memory cells
Secondary immune response
Looks like we are off to fight
This pathogen again!
But now we can respond
Faster with a larger army - those
Bugs won’t know what hit them!
Memory cells
divide
Memory cells
Antibody
molecules
Plasma cells
Memory cells
Antibody concentration
2nd response
Second exposure
occurs
to antigen X,
quicker with
first exposure
greater
to antigen Y
magnitude!!
Secondary immune
response to
antigen X
First exposure
to antigen X
Primary immune
response to
antigen X
Antibodies
to Y
Antibodies
to X
0
7
14
21
Primary immune
response to
antigen Y
35
28
Time (days)
42
49
56
Antibodies mark antigens for elimination
Binding of antibodies to antigens
inactivates antigens by
Neutralization
(blocks viral binding sites;
coats bacteria)
Virus
Agglutination
of microbes
Precipitation of
dissolved antigens
Activation of the
complement system
Complement
molecule
Bacteria
Antigen
molecules
Bacterium
Foreign cell
Enhances
Leads to
Phagocytosis
Cell lysis
Macrophage
Hole
T cell mediated immune function
 2 types of T cells:
– Helper T cells -- stimulate B-cell and T-cell mediated
immune responses
– Detect presence of forein antigens on SURFACE of virally
or bacterially infected body cells
– Cytotoxic T cells
– DESTROY infected cells as marked by Helper T cells
© 2012 Pearson Education, Inc.
Figure 24.UN01
The humoral immune response:
makes
which bind to
B cell
Antibodies
Antigens in
body fluid
The cell-mediated immune response:
T cell
Infected
body cell
Self-nonself complex
Figure 42.12 Macrophages Are Antigen-Presenting Cells
Infected body cells will
display antigens of pathogen
on cell surface
Phagocytic cell
(yellow) engulfing
a foreign cell
Self-nonself
complex
Macrophage
Microbe
B cell
T cell
receptor
Interleukin-2
stimulates
cell division
5
3
1
2
Helper
T cell
4
6
7
Interleukin-2
activates B cells
and other T cells
Self protein
Antigen from the microbe
(nonself molecule)
Antigen-presenting
cell
Binding
site for the
self protein
Binding
site for the
antigen
Humoral
immune
response
(secretion of
antibodies by
plasma cells)
Cytotoxic
T cell
Cell-mediated
immune
response
(attack on
infected cells)
Helper T cells are trained to recognize foreign
antigens and alert B cells and Cytotoxic T cells
Figure 42.6 The Specific Immune System
Figure 42.6 The Specific Immune System
How are B and T cells trained to recognize ‘self’
vs. ‘non-self’ antigens????
 Each of us display a unique protein and
carbohydrate ‘fingerprint’ on the surface of our cells
– This fingerprint is referred to as the MHC protein complex
 During development, B and T cells are exposed to
MHC proteins
 Any B or T cells that have antigen receptors that can
bind to ‘self’ antigens are DESTROYED!!
 This is called CLONAL DELETION.
© 2012 Pearson Education, Inc.
Figure 42.19 The Course of an HIV Infection
Figure 42.15 Heavy-Chain Genes
Figure 42.16 Heavy-Chain Gene Recombination and RNA Splicing
Figure 42.16 Heavy-Chain Gene Recombination and RNA Splicing (Part 1)
Figure 42.16 Heavy-Chain Gene Recombination and RNA Splicing (Part 2)
Figure 42.17 Class Switching: Exchanging C Regions
Figure 42.17 Class Switching: Exchanging C Regions