Chapter 43.

AP Biology 2008-2009

Chapter 43.

Immune System

lymphocytesattackingcancer cell

phagocytic leukocyte

lymphsystem


Why an immune system? Attack from outside

animals must defend themselves against unwelcome invaders viruses protists bacteria fungi

we are a tasty vitamin-packed meal cells are packages of macromolecules no cell wall

traded mobility for susceptibility

Attack from inside defend against abnormal body cells = cancers


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” 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: 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-baterial = “lick your wounds”

stomach acid pH 2-3

anti-microbial proteins lysozyme

digests bacterial cell walls


2nd: Internal, broad range patrol leukocytesleukocytes 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


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


Phagocytes

yeastmacrophage


Lymph systemProduction & transport of leukocytes

Traps foreign invaders

lymph node

lymph vessels(intertwined amongst blood vessels)


Development of Red & White blood cells

short-lived phagocytes60-70% WBC

develop into macrophages

inflammatory response

fightparasites

Red blood cells


Inflammatory response

Bacteria

Blood vessel

Chemicalalarm signals

Pin or splinterBlood clot

Phagocytes

swelling

Reaction to tissue damage


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


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

of iron to grow


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“self” “foreign”

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


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


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


Antibodies Proteins that bind to a specific antigen

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

“this is foreign!”

each B cell has ~100,000

antigen receptors

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variable binding region

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How antibodies work


B cell immune responsetested by

B cells

10 to 17 days for full response

invader(foreign antigen) B cells + antibodies

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recognition

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clone1000s of clone cellsY

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plasma cellsrelease antibodies

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memory cells“reserves”

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Ycapturedinvaders


1° vs 2° response to disease Memory B cells allow a rapid, amplified

response with future exposure to pathogen


How can we have so many antibody proteins & so few genes?

Light chain

Constant region

Transcriptionof gene

mRNA

Chromosome of undifferentiated B cell

B cell

CC

DJ

DNA ofdifferentiatedB cell

Rearrangement of DNA

VTranslation of mRNA

Antibody

40 genes for Variable region

Variable region

Heavy chain

Variable DNA combinations:

• 1M different B cells• 10M different T cells


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


Jonas Salk Developed first vaccine

against polio

1914 – 1995

April 12, 1955


Polio epidemics


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


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 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) human leukocyte antigens (HLA)

MHC proteins constantly export bits of cellular protein to cell surface “snapshot” of what is

going on inside cell

MHC proteinsdisplaying self-antigens

T cell


How do T cells know a cell is infected Infected cells digest some pathogens &

export pieces to MHC proteins on cell surface antigen presenting cells (APC)

T cell

MHC proteinsdisplaying foreign antigens

invading pathogen

T cell antigen receptors


T cell response

helperT cell

infected cell

activatedmacrophage

helperT cell

helperT cell

helperT cell

helperT cell stimulate

B cells &antibodies

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killerT cell

activatekiller T cells

orinterleukin 1

interleukin 2

interleukin 2


Attack of the Killer T cells

Killer T cellbinds toinfected

cell

Destroys infected body cells binds to target cell secretes perforin protein

punctures cell membrane of infected cell

Infected celldestroyed

Perforin puncturescell membrane

Cell membrane

Killer T cell

Cell membrane

Target cell

Vesicle


Immune responsepathogen invasion

antigenexposure

free antigens in blood antigens on infected cells

humoral response cellular response

B cells T cells

macrophages

helperT cells

plasmaB cells

memoryB cells

memoryT cells

cytotoxicT cells

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YantibodiesY 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 other

infections pneumonia or cancer


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


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

Chapter 43.

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