phagocytic
leukocyte
Fighting the
Enemy Within!
Immune / Lymphatic
System
AP Biology
lymphocytes
attacking
cancer cell
lymph
system
Objectives
 3 lines of defense
 Non-specific vs specific defense
 Active vs passive immunity
 Antibody structure and function
 Humoral vs cell-mediated responses
AP Biology
Agents of disease (PATHOGENS)
 Viruses
 Protists
 Bacteria
 Fungi
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How do diseases spread
 Physical contact
 Contaminated food and water
 Infected animals/ VECTORS

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Insects/ arachnids
Types of diseases
 Viral – measles, mumps, HIV, flu, cold,
chickenpox
 Bacterial – strep throat, cholera,
botulism, bubonic plague, staph
infection, Lyme’s disease
 Protist – dysentery, malaria, African
sleeping sickness
 Fungal – athletes foot, ringworm,
Candida, thrush
AP Biology
Avenues of attack
 Points of entry
digestive system
 respiratory system
 urogenital tract
 break in skin

 Routes of attack
circulatory system
 lymph system

AP Biology
Non-specific Defense
1. 1st: Barriers (skin/ mucous
membranes)
2. 2nd: Non-specific patrol (phagocytic
WBC’s)
3. 2nd: Immune Response
4. 2nd: Fever
1st Line of Defense
2nd Line of Defense
AP Biology
Non-specific Lines of defense
 1st line: Barriers

broad, external defense
 “walls & moats”
skin & mucus membranes
2nd line: Non-specific patrol
 broad, internal defense


 “patrolling soldiers”

leukocytes = phagocytic WBC
 macrophages
AP Biology
Bacteria & insects
inherit resistance.
Vertebrates
acquire immunity!
1st and 2nd lines of defense are
NON-SPECIFIC
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1st line: External defense
 Physical & chemical
defenses

non-specific defense
 external barrier

epithelial cells &
mucus membranes
 skin
 respiratory system
 digestive system
 uro-genital tract
AP Biology
Lining of trachea:
ciliated cells & mucus
secreting cells
1st line: Chemical barriers on epithelium
 Skin & mucous membrane secretions

sweat
 pH 3-5

tears
 washing action

mucus
 traps microbes

saliva
 anti-bacterial enzymes

stomach acid
 pH 2
AP Biology
2nd line: Internal, broad range patrol
leukocytes
 Innate, general defense

rapid response
 Patrolling cells & proteins

attack invaders that
penetrate body’s outer
barriers
 leukocytes
 phagocytic white blood cells
 Interferons
AP Biology
 complement system
 anti-microbial proteins
 inflammatory response
Interferons
 Interferons are proteins made and
released by host cells in response to
the presence of pathogens such as
viruses, bacteria, parasites or tumor
cells.
 Interferon therapy (IF) can be helpful in
alleviating symptoms of viral disease
but DO NOT eradicate the virus.
AP Biology
Phagocytes = eating cells
macrophage
AP Biology
yeast
2nd line: Inflammatory Response
 http://www.sumanasinc.com/webconten
t/animations/content/inflammatory.html
AP Biology
Inflammatory response
 Triggered by damage to

tissue
triggers local non-specific
inflammatory response

release histamines
 capillaries dilate,





AP Biology
more permeable (leaky)
increase blood supply
delivers WBC, RBC, platelets,
clotting factors
fight pathogens
clot formation
accounts for swelling, redness &
heat of inflammation & infection
Inflammatory response
 Reaction to tissue damage
Pin or splinter
Blood clot
swelling
Bacteria
Chemical
alarm signals
Phagocytes
Blood vessel
AP Biology
2nd line: Fever
 When a local response is not enough

higher temperature helps defense
 inhibits bacterial growth
 Increases heart rate – WBC’s can get to infection faster
 speeds up repair of tissues
 causes liver & spleen to store
iron, reducing blood iron levels
 bacteria need large amounts
of iron to grow
AP Biology
Non-specific Defense
 Barriers – 1st Line
 Non-specific patrol – 2nd Line
 Immune Response – 2nd Line
 Fever – 2nd Line
AP Biology
When this is not enough,
Our third line of defense kicks in
AP Biology
Specific Line of defense
 3rd line: Immune response

specific, acquired immunity
 “elite trained units”
Foreign invader (called an antigen)
triggers this response
 Cells involved

 Lymphocytes
 B cells
Humoral response
 T cells
 Cell-mediated response

AP Biology
Immune Response
 http://highered.mcgrawhill.com/sites/0072507470/student_view
0/chapter22/animation__the_immune_r
esponse.html
AP Biology
How are invaders recognized: antigens
 Antigens

proteins that serve as cellular name tags
 foreign antigens cause response from WBCs
 viruses, bacteria, protozoa, parasitic worms, fungi, toxins
 non-pathogens: pollen & transplanted tissue
 B cells & T cells respond to different antigens

B cells recognize intact antigens
 pathogens in blood & lymph

T cells recognize antigen fragments
 pathogens which have already infected cells
“self”
AP Biology
“foreign”
Key attributes of a good immune system
 4 attributes that characterize the
immune system as a whole

specificity
 antigen-antibody specificity

diversity
 react to millions of antigens

memory
 rapid 2° response

ability to distinguish self vs. non-self
 maturation & training process to reduce
auto-immune disease
AP Biology
B cells
 Humoral response = “in fluid”

defense against attackers circulating
freely in blood & lymph
 Specific response

produce specific antibodies
against specific antigen
 Types of B cells
AP Biology
 plasma cells
 immediate production of antibodies
 rapid response, short term release
 memory cells
 Stay in body
 Recognizes invader on future infections
 long term immunity
10 to 17 days for full response
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release antibodies
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plasma cells
AP Biology
recognition
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captured
invaders
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memory cells
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B cells + antibodies
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tested by
B cells
(in blood & lymph)
invader
(foreign antigen)
“reserves”
Y
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B cell immune response
clone
1000s of clone cells
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Antibodies
Y
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 Proteins that bind to a specific antigen
Y
antigens
tagging “handcuffs”
 “this is foreign…gotcha!”
Y

Y
 millions of antibodies respond to millions of foreign
Y

multi-chain proteins produced by B cells
binding region matches molecular shape of antigens
each antibody is unique & specific
Y
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
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
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antigenbinding site
on antibody
antigen
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variable
binding region
AP Biology
each B cell
has ~100,000
antigen receptors
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Structure of antibodies
Y
s
s
s
light
chain
B cell
membrane
AP Biology
s
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s
variable region
s
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antigen-binding site
light
chain
heavy
chains
light chains
antigen-binding
site
heavy chains
antigen-binding
site
How antibodies work
invading pathogens
tagged with
antibodies
macrophage
eating tagged invaders
AP Biology
Y
Huh?
 Antibodies = proteins (Y-shaped)…
DEFEND you against pathogens.

Your body makes these in response to
antigens
 Antigens = proteins that GENerate the
immune response (are bound up by
antibodies)
AP Biology
1° vs 2° response to disease
 Memory B cells allow a rapid, amplified
response with future exposure to pathogen
AP Biology
Vaccinations
 Immune system exposed
to harmless version of pathogen
triggers active immunity
 stimulates immune system to produce
antibodies to invader
 rapid response if
future exposure

 Most successful
against viral diseases
AP Biology
Passive immunity
 Obtaining antibodies from another
individual
 Maternal immunity
antibodies pass from mother to baby across
placenta or in mother’s milk
 critical role of breastfeeding in infant health

 mother is creating antibodies against pathogens
baby is being exposed to
 Injection
injection of antibodies
 short-term immunity

AP Biology
What if the attacker gets past the
B cells in the blood & actually
infects some of your cells?
You need trained assassins
to kill off these infected cells!
Attack
of the
Killer T cells!
AP Biology
T cells
 Cell-mediated response

immune response to infected cells
 viruses, bacteria & parasites (pathogens)
within cells

defense against “non-self” cells
 cancer & transplant cells
 Types of T cells

helper T cells
 alerts immune system

killer (cytotoxic) T cells
 attack infected body cells
AP Biology
How do T cells know a cell is infected
 Infected cells digest pathogens & MHC
proteins bind & carry pieces to cell surface
antigen presenting cells (APC)
 alerts Helper T cells

infected
cell
WANTED
AP Biology
MHC proteins displaying
foreign antigens
T cell
T cell
antigen receptors
T cell response
infected cell
killer
T cell
helper
T cell
interleukin 1
or
activated
macrophage
activate
killer T cells
helper
T cell
helper
T cell
stimulate
B cells &
antibodies
helper
T cell
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AP Biology
Y
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helper
T cell
Y
Y
HIV & AIDS
 Human Immunodeficiency Virus
virus infects helper T cells
 helper T cells don’t activate rest of
immune system: T cells & B cells

 also destroy T cells
 Acquired ImmunoDeficiency Syndrome
infections by opportunistic
diseases
 death usually from secondary
infections

 pneumonia, cancer
AP Biology
Immune system malfunctions
 Auto-immune diseases

immune system attacks own molecules & cells
 lupus
 antibodies against many molecules released by normal
breakdown of cells
 rheumatoid arthritis
 antibodies causing damage to cartilage & bone
 diabetes
 beta-islet cells of pancreas attacked & destroyed
 multiple sclerosis
 T cells attack myelin sheath of brain & spinal cord nerves
 Allergies

over-reaction to environmental antigens
 allergens = proteins on pollen, dust mites, in animal
AP Biology
saliva
 stimulates release of histamine
AP Biology
Immunity
 The 3 lines of defense
 Non-specific vs. specific
 Acquired vs. passive immunity
 Humoral vs. Cell-mediated response
AP Biology