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Susan Capasso, Ed.D., CGCSt. Vincent’s College
Suggested Lecture Presentation
Copyright © 2009 Pearson Education, Inc.
Chapter 13
Body Defense Mechanisms
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Body Defense Mechanisms
The body’s defense system targets pathogens and cancerous cells
The body has three lines of defense The immune system distinguishes self
from nonself The immune system mounts antibody-
mediated responses and cell-mediated responses
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Body Defense Mechanisms
The cell-mediated immune response and the antibody-mediated immune response have the same steps
Immunity can be active or passive Monoclonal antibodies are used in
research, clinical diagnosis, and disease treatment
The immune system can cause problems
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The Body’s Defense System
The body’s defense mechanisms target pathogens and cancerous cells
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The Body Has 3 Lines of Defense
The body has three lines of defense Nonspecific
1. Physical and chemical surface barriers
2. Internal cellular and chemical defense Specific
3. Immune response
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The Body Has 3 Lines of Defense
Figure 13.1
First line of defense:Nonspecific physical andchemical surface barriers
Second line of defense:Nonspecific internal cellular
and chemical defense
Third line of defense:Immune response
Specific defensesNonspecific defenses
If pathogenpenetrates barriers
If pathogensurvives nonspecific
internal defenses
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Nonspecific Surface Barriers
Physical and chemical barriers The skin
Nearly impenetrable Waterproof Resistant to most toxins and enzymes of
invading organisms Sweat and oil glands
Produce chemicals that slow or prevent the growth of bacteria
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Nonspecific Surface Barriers
Physical and chemical barriers (continued) Mucus of the respiratory and digestive tracts
Sticky and traps many microbes The lining of the stomach
Produces hydrochloric acid and digesting enzymes that destroy pathogens
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Nonspecific Surface Barriers
Physical and chemical barriers (continued) Urine
Slows bacterial growth with acidity Washes microbes from urethra
Saliva and tears Contain lysozyme, an enzyme that kills
bacteria
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Nonspecific Surface Barriers
Figure 13.2 (1 of 2)
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Nonspecific Surface Barriers
Figure 13.2 (2 of 2)
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Nonspecific Internal Defenses
The second line of defense Defensive cells Defensive proteins Inflammation Fever
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Nonspecific Internal Defenses
Table 13.1
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Nonspecific Internal Defenses
Animation—The Inflammatory ResponsePLAY
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Nonspecific Internal Defenses
Defensive cells include neutrophils and macrophages They engulf pathogens, damaged tissue, or
dead cells by the process of phagocytosis
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Nonspecific Internal Defenses
Figure 13.3
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Nonspecific Internal Defenses
Eosinophils Attack pathogens that are too large for
phagocytosis, such as parasitic worms Get close to the parasites and discharge
destructive enzymes that destroy them
Natural killer (NK) cells Search out abnormal cells, including
cancerous cells, and kill them
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Nonspecific Internal Defenses
Figure 13.4
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Nonspecific Internal Defenses
The body’s non-specific cellular defenses use two types of defensive proteins Interferons Complement system
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Nonspecific Internal Defenses
Before a virally–infected cell dies, it secretes small proteins called interferons that Attract macrophages and natural killer cells Stimulate neighboring cells to make proteins
that prevent the viruses from replicating
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Nonspecific Internal Defenses
The complement system A group of proteins that enhance both
nonspecific and specific defense mechanisms by Destroying pathogens Enhancing phagocytosis Stimulating the inflammatory response
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Nonspecific Internal Defenses
Figure 13.5 (1 of 3)
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Nonspecific Internal Defenses
Figure 13.5 (2 of 3)
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Nonspecific Internal Defenses
Figure 13.5 (3 of 3)
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Nonspecific Internal Defenses
Inflammatory response destroys invaders and helps repair and restore damaged tissue Redness Heat Swelling Pain
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Nonspecific Internal Defenses
Figure 13.6 (1 of 2)
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Nonspecific Internal Defenses
Figure 13.6 (2 of 2)
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Nonspecific Internal Defenses
The increased blood flow to damaged tissue stimulates mast cells and basophils to release histamine Increases blood flow by dilating blood
vessels and increasing the permeability of the capillaries
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Nonspecific Internal Defenses
Fluid leaks from the capillaries Causes swelling
Blood flow increases Causes redness and warmth
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Nonspecific Internal Defenses
Fever An abnormally high body temperature
caused by pyrogens Chemicals that reset the brain’s
thermostat to a higher temperature
A moderately higher body temperature helps fight bacterial infections
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Nonspecific Internal Defenses
Figure 13.7
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Nonspecific Internal Defenses
Table 13.1
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Specific Immune Responses
The third line of defense is the immune system Has specific responses and memory
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Specific Immune Responses
Immune response The body’s specific defenses Work together in the recognition and
destruction of specific pathogens Have memory
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The Immune System Distinguishes Self from Nonself
The body must be able to distinguish a foreign organism or molecule from self
MHC markers are found on our own cells and mark them as belonging to us
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The Immune System Distinguishes Self from Nonself
Figure 13.8
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The Immune System
Antigens Nonself substances that trigger an immune
response Usually large molecules, such as proteins,
polysaccharides, or nucleic acids
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The Immune System
When an antigen is detected B lymphocytes and T lymphocytes that
recognize the antigen are stimulated to divide repeatedly
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The Immune System
Some of these cells attack and eliminate the invader
Others are stored in a state of suspended animation as a form of memory of the invader Available to attack if there is a reoccurrence
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Antibody-Mediated Responses
Antibody-mediated immune responses Defend against antigens that are free in
body fluids, including toxins or extracellular pathogens
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Antibody-Mediated Responses
B cells use antibodies to neutralize the antigen
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Antibody-Mediated Responses
Figure 13.9 (1 of 3)
Antigen
Macrophage
Helper T cell
Effectorhelper T cell
Memoryhelper T cell
Naive B cell Naivecytotoxic T cell
Antibody-mediated response
Engulfed
Cell divides
Cell divides
Activates Activates
Presents antigen toidentify invader andactivates helper T cells
Step 1: Threat
Step 2: Detection
Step 3: Alert
Step 4: Alarm Step 4: Alarm
Step 7: Continuedsurveillance
Cell-mediated response
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Antibody-Mediated Responses
Figure 13.9 (2 of 3)
Effectorhelper T cell
Naive B cell
Plasma cell
Antibodies
Memory B cell
Secretes
Antibody-mediated response
Memory cellsremain and providea quick response tothe antigen in afuture encounter
Cell divides
Activates
Step 4: Alarm
Step 7: Continuedsurveillance
Step 6: Defense
Step 5: Buildingspecific defenses
Pathogens or toxinsoutside of cells
Targets
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Antibody-Mediated Responses
Figure 13.12 (1 of 2)
Step 4: AlarmThe helper T cell stimulatesthe B cell to begin dividing.
Step 5: Buildingspecific defensesThe B cell divides andforms plasma cells andmemory cells.
Memory B cell
B cell
B cell
B cell
Helper T cell
Plasma cell
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Antibody-Mediated Responses
Figure 13.12 (2 of 2)
Step 5: Buildingspecific defensesThe B cell divides andforms plasma cells andmemory cells.
Step 6: DefensePlasma cells secreteantibodies specificfor that antigen.
Step 7: ContinuedsurveillanceMemory B cells remain andmount a quick response ifthe invader is encounteredagain.
Memory B cells
Memory B cell
B cell
Plasma cell
Antibodies
Plasma cell
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Cell-Mediated Responses
Cell-mediated immune responses Involve living cells Protect against cellular threats, including
body cells that have become infected and cancer cells
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Cell-Mediated Responses
Figure 13.9 (1 of 3)
Antigen
Macrophage
Helper T cell
Effectorhelper T cell
Memoryhelper T cell
Naive B cell Naivecytotoxic T cell
Antibody-mediated response
Engulfed
Cell divides
Cell divides
Activates Activates
Presents antigen toidentify invader andactivates helper T cells
Step 1: Threat
Step 2: Detection
Step 3: Alert
Step 4: Alarm Step 4: Alarm
Step 7: Continuedsurveillance
Cell-mediated response
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Cell-Mediated Responses
Figure 13.9 (3 of 3)
Effectorhelper T cell
Effectorcytotoxic T cell
Memorycytotoxic T cell
Naivecytotoxic T cell
Memory cellsremain and providea quick response tothe antigen in afuture encounter
Cell divides
Activates
Step 4: Alarm
Step 7: Continuedsurveillance
Step 6: Defense
Step 5: Buildingspecific defenses
Cells infected with intracellularpathogen; cancer cells; cells oforgan transplants
Targets
Cell-mediated response
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Cell-Mediated Responses
Figure 13.14 (1 of 2)
Step 5: Building specificdefensesThe cytotoxic T cell dividesand forms effector cytotoxicT cells and memorycytotoxic T cells. Memory
cytotoxic T cell
Effectorcytotoxic T cell
Step 4: AlarmThe helper T cell stimulates anaive or memory cytotoxic Tcell to begin dividing.
Helper T cell
Cytotoxic T cell
Antigen
Virus
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Cell-Mediated Responses
Figure 13.14 (2 of 2)
Step 5: Building specificdefensesThe cytotoxic T cell dividesand forms effector cytotoxicT cells and memorycytotoxic T cells.
Step 6: DefenseEffector cytotoxic cellscause the target cell toburst and die. In this case,the target cell is a cellinfected with a virus thattriggered the response.
Step 7: ContinuedsurveillanceMemory cytotoxic T cellsremain and mount a quickresponse if the invader isencountered again.
Memory cytotoxic T cells
Memorycytotoxic T cell
Target cell
Effectorcytotoxic T cell
Perforin
T cell membrane
Target cell membrane
Perforin assemblinginto pores
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Cell-Mediated Responses
Table 13.2 (1 of 2)
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Cell-Mediated Responses
Table 13.2 (2 of 2)
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Cell-Mediated Responses
Table 13.3 (1 of 2)
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Cell-Mediated Responses
Table 13.3 (2 of 2)
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Cell-Mediated Responses
Animation—Antibody- and Cell-Mediated ImmunityPLAY
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Immune Response Steps
1. Threat Foreign cell or molecule enters the body
2. Detection Macrophage detects foreign cell or
molecule and engulfs it
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Immune Response Steps
3. Alert Macrophages present antigens to helper
T- cells to trigger an immune response They are called antigen-presenting cells
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Immune Response Steps
Figure 13.10
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Immune Response Steps
4. Helper T cells activate B cells and T cells to destroy the specific antigen When activated, these cells divide to form
clones of cells designed to eliminate a specific antigen from the body
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Immune Response Steps
Figure 13.11 (1 of 2)
The selected B celldivides, producing aclone of cells all bearingreceptors specific forthat particular antigen.
The antigen binds to theB cell with appropriatereceptors.
This B cell hasreceptors specificfor this particularantigen.
There is atremendousvariety of B cells.Each B cell hasreceptors for adifferent antigenon its surface.
Antigen
B cells
B-cellreceptorreceptor
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Immune Response Steps
Figure 13.11 (2 of 2)
Plasma cells produceantibodies specific forthis particular antigen.
Memory cells remainto bring about a quickresponse to thatantigen in the future.
The selected B celldivides, producing aclone of cells all bearingreceptors specific forthat particular antigen.
Plasmacells
Memory cells
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Immune Response Steps
5. Specific defense mechanism is built B cells form plasma cells that secrete
antibodies into the bloodstream that bind to antigens
T cells form cytotoxic T cells that attack
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Immune Response Steps
Figure 13.12 (1 of 2)
Step 4: AlarmThe helper T cell stimulatesthe B cell to begin dividing.
Step 5: Buildingspecific defensesThe B cell divides andforms plasma cells andmemory cells.
Memory B cell
B cell
B cell
B cell
Helper T cell
Plasma cell
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Immune Response Steps
Figure 13.12 (2 of 2)
Step 5: Buildingspecific defensesThe B cell divides andforms plasma cells andmemory cells.
Step 6: DefensePlasma cells secreteantibodies specificfor that antigen.
Step 7: ContinuedsurveillanceMemory B cells remain andmount a quick response ifthe invader is encounteredagain.
Memory B cells
Memory B cell
B cell
Plasma cell
Antibodies
Plasma cell
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Immune Response Steps
6. Primary defense Antibodies specific to the antigen eliminate
the antigen Cytotoxic T cells release perforins that
cause cells with the antigen to burst
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Immune Response Steps
Immunoglobulins Five classes of antibodies, each with a
special role to play in protecting against invaders IgG IgM IgE IgA IgD
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Immune Response Steps
Figure 13.13
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Immune Response Steps
Table 13.4
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Immune Response Steps
7. Immunological memory Allows for a more rapid response on
subsequent exposure to the antigen Primary response may be slow as the
antibody concentration rises Secondary response is strong and swift
due to the large number of specific memory cells that can respond to the antigen
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Immune Response Steps
Figure 13.15
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Immune Response Steps
8. Suppressor T cells Turn off the immune response when the
antigens no longer pose a threat
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Active Immunity
Active immunity The body actively participates by producing
memory B cells and T cells following exposure to an antigen
This process can also happen through vaccination
Because memory cells are produced, active immunity is relatively long lived
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Passive Immunity
Passive immunity Results when a person receives antibodies
that were produced by another person or animal
Short lived since the recipient’s body was not stimulated to produce memory cells
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Monoclonal Antibodies
Monoclonal antibodies A group of identical antibodies that bind to
one specific antigen Used in research, clinical diagnosis, and
disease treatment because they can help diagnose certain diseases in their early stages
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The Immune System Can Cause Problems
Autoimmune disorders Failure to recognize distinguish between self
and nonself Occur when the immune system attacks the
body’s own cells
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The Immune System Can Cause Problems
Figure 13.16
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Immune System Problems
Allergies Immune responses to harmless substances
called allergens Allergens cause plasma cells to release
large numbers of class IgE antibodies
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Immune System Problems
Figure 13.17
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Immune System Problems
Table 13.6
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Immune System Problems
These IgE class antibodies bind to mast cells or basophils, causing them to release histamine
The histamine causes redness, swelling, itching, and other symptoms of an allergic response
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Immune System Problems
Figure 13.18 (1 of 2)Mast cell
Plasma cell
Allergen
IgE antibody
Granulescontaininghistamine
First exposure
Step 1: The invader (allergen)enters the body.
Step 2: Plasma cells producelarge amounts of class IgEantibodies against theallergen.
Step 3: IgE antibodies attachto mast cells, which are foundin body tissues.
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Immune System Problems
Figure 13.18 (2 of 2)
Subsequent (secondary) response
Antigen
Histamine
Step 4: More of the sameallergen invades the body.
Step 5: The allergencombines with IgE attachedto mast cells. Histamine andother chemicals are releasedfrom mast cell granules.
• Histamine stimulates releaseof large amounts of mucus.
• Histamine causes smoothmuscle in walls of air tubulesin lungs to contract.
Step 6: Histamine causesblood vessels to widen andbecome leaky. Fluid entersthe tissue, causing swelling.
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Immune System Problems
Antihistamines are most effective in reducing the allergy symptoms
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Immune System Problems
Allergy shots inject increasing amounts of a known allergen in an effort to desensitize the person to the offending allergens