phagocytic
leukocyte
Chapter 43.
Immune System
AP Biology
lymphocytes
attacking
cancer cell
lymph
system
2008-2009
Why an immune system?
 Attack from outside

animals must defend themselves against
unwelcome invaders
 viruses
 bacteria

protists
 fungi

we are a tasty vitamin-packed meal
 cells are packages of macromolecules
 no cell wall
 traded mobility for susceptibility
 Attack from inside

AP Biology
defend against abnormal body cells = cancers
2008-2009
Lines of defense
 1st line: Barriers

broad, innate, external defense
 “barbed wire”

skin & mucus membranes
 2nd line: Non-specific patrol

broad, innate, internal defense
 “untrained soldiers”

leukocytes (WBCs)
 3rd line: Immune system

specific, acquired immunity
 “elite trained units”

AP Biology
lymphocytes & antibodies
2008-2009
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
2008-2009
1st: Chemical barriers on epithelium
 Skin & mucous membrane secretions

sweat
 pH 3-5

tears
 washing action

mucus
 traps microbes

saliva
 anti-baterial = “lick your wounds”

stomach acid
 pH 2-3

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anti-microbial proteins
 lysozyme
 digests bacterial cell walls
2008-2009
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
 natural killer cells
AP Biology
2008-2009
Leukocytes: Phagocytic WBCs
 Neutrophils
attracted by chemical signals released
by damaged cells (interferon)
 enter infected tissue, engulf & ingest
microbes

 amoeba-like
 lysosomes
 ~3 day life span
 Macrophages
“big eater”
 bigger, long-lived
phagocytes
AP Biology

2008-2009
Phagocytes
macrophage
AP Biology
yeast
2008-2009
Lymph system
Production & transport of leukocytes
Traps foreign invaders
lymph vessels
(intertwined amongst blood vessels)
AP Biology
lymph node
2008-2009
Development of Red & White blood cells
Red blood cells
inflammatory
response
fight
parasites
AP Biology
develop into
macrophages
short-lived phagocytes
2008-2009
60-70% WBC
Inflammatory response
 Reaction to tissue damage
Pin or splinter
Blood clot
swelling
Bacteria
Chemical
alarm signals
Phagocytes
Blood vessel
AP Biology
2008-2009
Inflammatory response
 Damage to tissue triggers
local inflammatory
response

histamines & prostaglandins
released
 capillaries dilate,
more permeable
 lead to clot formation

increased blood supply
 swelling, redness & heat of
inflammation & infection
 delivers WBC, RBC, platelets,
clotting factors
AP Biology
2008-2009
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
AP Biology
of iron to grow
2008-2009
3rd: Acquired Immunity
 Specific defense

lymphocytes
 B lymphocytes (B cells)
 T lymphocytes (T cells)

antibodies
 immunoglobulins
 Responds to…
specific microorganisms
 specific toxins
 abnormal body cells
 antigens

AP Biology
2008-2009
Antigens
 Proteins that serve as cellular name tags


foreign antigens cause response from WBCs
proteins belonging:
 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”
AP Biology
“foreign”
2008-2009
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
AP Biology
2008-2009
B cells
 Humoral response = “in fluid”

defense against attackers circulating freely
in blood & lymph
 Specific response


recognizes specific antigen
produces antibodies against it
 tagging protein = immunogloblin
 millions of different B cells,
each produces different antibodies,
each recognizes a different antigen

types of B cells
 plasma cells
 immediate production of antibodies
 short term release
 memory cells
 long term immunity
AP Biology
2008-2009
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
Y
Y
Y
 Proteins that bind to a specific antigen

Y
Y
Antibodies
Y
Y
Y
 “this is foreign!”
Y
variable binding region
Y
Y
Y
each B cell
has ~100,000
antigen receptors
AP Biology
2008-2009
How antibodies work
AP Biology
2008-2009
10 to 17 days for full response
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
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Y 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
captured
invaders
Y
Y
Y
B cells + antibodies
Y
Y
memory cells
“reserves”
Y
invader
(foreign antigen)
Y
Y
Y
Y
tested by
B cells
Y
Y
B cell immune response
clone
1000s of clone cells
2008-2009
1° vs 2° response to disease
 Memory B cells allow a rapid, amplified
response with future exposure to pathogen
AP Biology
2008-2009
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
AP Biology
Rearrangement
of DNA
V
40 genes for
Variable region
D
C
J
Chromosome
2008-2009 B cell
of undifferentiated
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
AP Biology
2008-2009
1914 – 1995
Jonas Salk
 Developed first vaccine

against polio
April 12, 1955
AP Biology
2008-2009
Polio epidemics
AP Biology
2008-2009
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
2008-2009
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
2008-2009
How are cells tagged with antigens
 Glycoproteins on surface of cells have
unique “fingerprint”
major histocompatibility proteins (MHC)
 human leukocyte antigens (HLA)

 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
2008-2009
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
2008-2009
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
2008-2009
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
2008-2009
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
AP Biology
memory
B cells
Y
plasma
B cells
Y
antigens on infected cells
memory
T cells
cytotoxic
T cells
2008-2009
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 other
infections

 pneumonia or cancer
AP Biology
2008-2009
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
AP Biology
2008-2009
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
2008-2009