phagocytic
leukocyte
“Fighting the
Enemy Within”
Immune System
Chapter 51
AP Biology
lymphocytes
attacking
cancer cell
lymph
system
2006-2007
Avenues of attack
 Points of entry
digestive system
 respiratory system
 urogenital tract
 break in skin

 Routes of attack
circulatory system
 lymph system

AP Biology
Why an immune system?
 Attack from outside


lots of organisms want you for lunch!
animals must defend themselves against
unwelcome invaders
 viruses
 bacteria

All in a
good day’s
work!
protists
 fungi

we are a tasty vitamin-packed meal
 cells are packages of macromolecules
 no cell wall
 traded mobility for susceptibility
 Attack from inside

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defend against abnormal body cells = cancers
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 WBCs)
 3rd line: Immune system

specific, acquired immunity
 “elite trained units”

AP Biology
lymphocytes & antibodies
1st: External defense
 non-specific defense
 external barrier

epithelial cells &
mucus membranes
 skin
 respiratory system
 digestive system
 genito-urinary tract
Lining of trachea:
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ciliated cells & mucus
secreting cells
1st: Chemical barriers on epithelium
 Skin & mucous membrane secretions

sweat
 pH 3-5

tears
 washing action

mucus
 traps microbes

saliva
 anti-bacterial = “lick your wounds”

stomach acid
 pH 2

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anti-microbial proteins
 lysozyme
 digests bacterial cell walls
2nd: Internal, broad range patrol
leukocytes
 innate defense
 rapid response
 cells & proteins

attack invaders that
penetrate body’s outer
barriers
 leukocytes
 phagocytic white blood cells
 anti-microbial proteins
 inflammatory response
AP Biology
Leukocytes: Phagocytic WBCs
 Neutrophils
attracted by chemical signals released
by damaged cells
 enter infected tissue, engulf & ingest
microbes

 amoeba-like (fierce!)
 digest via lysosomes
 ~3 day life span
 Macrophages
“big eater”
 bigger, long-lived
phagocytes
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
Phagocytes
macrophage
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yeast
Lymph system
Production & transport of leukocytes
Traps foreign invaders
lymph vessels
(intertwined amongst blood vessels)
AP Biology
lymph node
Development of Red & White blood cells
inflammatory
response
Red blood cells
fight
parasites
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develop into
macrophages
short-lived phagocytes
60-70% WBC
Inflammatory response
 Damage to tissue triggers
local inflammatory
response


release histamines &
prostaglandins
capillaries dilate,
more permeable
 increase blood supply
 delivers WBC, RBC, platelets,
clotting factors
 lead to clot formation
 swelling, redness & heat of
inflammation & infection
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Inflammatory response
 Reaction to tissue damage
Pin or splinter
Blood clot
swelling
Bacteria
Chemical
alarm signals
Phagocytes
Blood vessel
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Fever
 When a local response is not enough

systemic response to infection

activated macrophages release interleukin-1
 triggers hypothalamus in brain to readjust body
thermostat to raise body temperature

higher temperature helps defense
 inhibits bacterial growth
 stimulates phagocytosis
 speeds up repair of tissues
 causes liver & spleen to store
iron reducing blood iron levels
 bacteria need large amounts
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of iron to grow
3rd: Acquired Immunity
 Specific defense

lymphocytes
 B lymphocytes (B cells)
 T lymphocytes (T cells)

antibodies
 immunoglobulins
 Responds to…

antigens
 specific microorganisms
 specific toxins
 abnormal body cells
AP Biology
Antigens
 Proteins that serve as cellular name tags


foreign antigens cause response from WBCs
proteins belonging to:
 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
 invaders in blood & lymph

T cells recognize antigen fragments
 invaders which have infected cells
“self”
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“foreign”
Lymphocytes
 B cells


mature in bone marrow
humoral response system
 “humors” = body fluids
 produce antibodies
 T cells


mature in thymus
cellular response system
 Learn to distinguish
“self” from “non-self”
antigens during maturation
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B cells
 Humoral response = “in fluid”

defense against attackers circulating freely
in blood & lymph
 Specific response

produces antibodies against
specific antigen
 tagging protein = immunogloblin
 millions of different B cells,
each produces different antibodies,
each recognizes a different antigen

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types of B cells
 plasma cells
 immediate production of antibodies
 short term release
 memory cells
 long term immunity
Y
 “this is foreign!”
variable
binding region
Y
Y
Y
Y
Y

Y
Y

Y
Y

multi-chain proteins produced by B cells
antibodies match molecular shape of antigens
immune system has antibodies to respond to
millions of antigens (invaders)
tagging system
Y
Y

Y
 Proteins that bind to a specific antigen
Y
Y
Antibodies
Y
Y
Y
Y
Y
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Y
Y
each B cell
has ~100,000
antigen receptors
How antibodies work
AP Biology
10 to 17 days for full response
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
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Y
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Y
Y Y
Y
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Y Y
Y
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release antibodies
Y
Y
plasma cells
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recognition
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
captured
invaders
Y
memory cells
Y
B cells + antibodies
Y
Y
Y
Y
Y
tested by
B cells
(in blood & lymph)
invader
(foreign antigen)
“reserves”
Y
Y
B cell immune response
clone
1000s of clone cells
1° vs 2° response to disease
 Memory B cells allow a rapid, amplified
response with future exposure to pathogen
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How can we
have so many
antibody
proteins &
so few genes?
Variable region
Antibody
Constant region
Light chain
B cell
Heavy chain
Variable DNA
combinations:
Transcription
of gene
• 1M different B cells
• 10M different T cells
mRNA
DNA of
differentiated
B cell
C
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Rearrangement
of DNA
V
40 genes for
Variable region
D
C
J
Chromosome
of undifferentiated B cell
Vaccinations
 Active immunity

immune system exposed to
harmless version of pathogen
 Stimulates immune system to produce
antibodies to invader

rapid response if
future exposure
 Most successful
against viral diseases
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1914 – 1995
Jonas Salk
 Developed first vaccine

against polio
April 12, 1955
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Polio epidemics
1994:
Americas polio free
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Passive immunity
 Maternal immunity
antibodies pass from mother to baby
across placenta or in breast 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
T cells
 Immune response to infected cells

defense against invaders inside
infected cells
 viruses & bacteria within infected cells,
fungi, protozoa & parasitic worms

defense against “non-self” cells
 cancer & transplant cells
 Kinds of T cells

helper T cells
 stimulate immune system

AP Biology
killer T cells
 attack infected body cells
How are cells tagged with antigens
 Glycoproteins on surface of cells have
unique “fingerprint”

major histocompatibility proteins (MHC)
 MHC proteins constantly export bits of
cellular protein to cell surface

“snapshot” of what is
going on inside cell
T cell
MHC proteins
displaying self-antigens
AP Biology
How do T cells know a cell is infected
 Infected cells digest some pathogens &
export pieces to MHC proteins on cell
surface

invading
pathogen
antigen presenting cells (APC)
MHC proteins
displaying
foreign antigens
T cell
AP Biology
T cell antigen
receptors
T cell response
infected cell
helper
T cell
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
helper
T cell
AP Biology
stimulate
B cells &
antibodies
Y
activated
macrophage
Y
or
helper
T cell
helper
T cell
Y
interleukin 1
activate
killer T cells
Y
helper
T cell
killer
T cell
Attack of the Killer T cells
 Destroys infected body cells
binds to target cell
 secretes perforin protein

 punctures cell membrane of infected cell
Killer T cell
Killer T cell
binds to
infected
cell
Vesicle
Cell
membrane
Perforin
punctures
cell membrane
Cell
membrane
AP Biology
Infected cell
destroyed
Target cell
Immune response
pathogen invasion
antigen
exposure
free antigens in blood
humoral response
macrophages
cellular response
B cells
helper
T cells
T cells
Y
Y
Y
Y
Y
Y
Y
Y
Y antibodies
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memory
B cells
Y
plasma
B cells
Y
antigens on infected cells
memory
T cells
cytotoxic
T cells
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, from dust mites, in
animal saliva -IgE
AP Biology
Key attributes of 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
Any Questions??
AP Biology
2006-2007