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BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition

Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor

From PowerPoint Lectures forBiology: Concepts & Connections

CHAPTER 24The Immune System

Modules 24.124.2

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Acquired immune deficiency syndrome (AIDS)

is epidemic throughout much of the world

14,000 people are infected with the AIDS virusevery day

HIV is the virus that causes AIDS

HIV is transmitted mainlyin blood and semen

Former L.A. Laker MagicJohnson is one of 900,000

Americans who areHIV-positive

The Continuing Problem of HIV

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Our immune system is a specific defense system

It backs up several mechanisms ofnonspecific resistance

HIV attacks the immune system

It eventually destroys the bodys ability tofight infection

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Basic Mechanisms of Defense

There are three basic lines of defense againstdisease

Vertebrate have all three lines of defense

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The 1st line of defense:nonspecific external barriers

Prevent microbes from entering the body

Examples: skin and mucous membranes

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The 2nd line of defense:nonspecific internal barriers

Occurs when microbes breach nonspecificexternal barriers

Broad internal responses to microbe infection

Examples: phagocytic white blood cells,inflammation, fever

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The 3rd line of defense:specific immune response

Immune cells selectively destroy specificinvading microbes and toxins

Invaders are remembered, allowing for a

rapid future response to invasion

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The bodys first lines of defense againstinfection are nonspecific

They do not distinguish one infectious microbefrom another

24.1 Nonspecific defenses against infection include

the skin and mucous membranes, phagocyticcells, and antimicrobial proteins

NONSPECIFIC DEFENSES AGAINSTINFECTION

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Skin and Mucous Membranes

The skin is important in blocking microbeentry and suppressing microbe growth

Skin is a barrier to microbes

Skin is continually shed, removing microbesthat gain a foothold on skin

Many skin secretions contain naturalantibiotics

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Skin and Mucous Membranes

Mucous membranes have effective microbedefense mechanisms

Mucous membrane secretions containantibacterial enzymes (example: lysozymes)

Mucus traps microbes entering the nose or

mouth

Respiratory tract cilia sweep mucus andmicrobes away from lungs

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Nonspecific Internal Defenses

Broad defenses that attack microbes thatpenetrate the skin

Three major categories of nonspecificinternal defenses

Phagocytic cells and natural killer cells

The inflammatory response

Fever

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Macrophages wander in the interstitial fluid

They eat any bacteria and virus-infectedcells they encounter

Figure 24.1A

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Natural Killer Cells

A type of white blood cell

Attack body cells that are cancerous or

infected with virus

Secrete enzymes that poke holes in the cellmembrane of virally-infected or cancerous

cells

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Fever

Helps combat large-scale infection byelevating body temperature

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Fever

Some cells release cytokines in response toinfection

Antibacterial cytokines

Macrophages release endogenous pyrogens:elevate body temperature

Other cytokines: decrease iron in the blood

Both act to slow bacterial reproduction

Antiviral cytokines:Interferon, which helpscells resist viral attack

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Interferon and complement proteins areactivated by infected cells

Figure 24.1B

1

2

3

4

Interferongenes

turned on

Interferonmolecules

5 Interferonstimulatescell to turnon genesfor antiviralproteins

HOST CELL 2Protected against virusby interferon from cell 1

HOST CELL 1Makes interferon;is killed by virus

Antiviral proteins blockviral reproduction

VIRUS Viral nucleic acid

mRNA

New viruses

6

24 2 i f i i

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Tissue damage triggers the inflammatoryresponse

24.2 The inflammatory response mobilizesnonspecific defense forces

Figure 24.2

Tissue injury; release ofchemical signals such ashistamine

1 2 3Dilation and increased leakinessof local blood vessels; migrationof phagocytes to the area

Phagocytes (macrophages andneutrophils) consume bacteriaand cell debris; tissue heals

PinSkin surface

BacteriaChemicalsignals

Whiteblood cell

Swelling

Phagocytes andfluid moveinto area

Phagocytes

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The inflammatory response can

disinfect tissues limit further infection

24 3 Th l h ti t b i l

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The lymphatic system is a network oflymphatic vessels and organs

It returns tissue fluid to the circulatory system

It fights infections

24.3 The lymphatic system becomes a crucialbattleground during infection

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Figure 23.3

Right lymphatic

duct, enteringveinThoracicductAppendix

AdenoidTonsil

Lymph nodesThoracic duct,entering vein

ThymusSpleen

Bonemarrow Lymphatic

vessels

LYMPHATICVESSELVALVEBloodcapillary

Tissue cellsInterstitialfluid

LYMPHATICCAPILLARY

Masses oflymphocytes andmacrophages

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This lymphatic vessel is taking up fluid fromtissue spaces in the skin

It will return it as lymph to the blood

Lymph contains less oxygen and fewernutrients than interstitial fluid

Figure 23.3B

LYMPHATICVESSELVALVE

Bloodcapillary

Interstitialfluid

LYMPHATICCAPILLARY

Tissue cells

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Lymph nodes are key sites for fighting infection

They are packed with lymphocytes and

macrophages

Figure 23.3C, D

Masses oflymphocytes and

macrophages

Lymphocytes

Macrophages

Outer capsule oflymph node

SPECIFIC IMMUNITY

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Our immune systems responds to foreignmolecules called antigens

Infection or vaccination triggers activeimmunity

The immune system reacts to antigens and

remembers an invader

We can temporarily acquire passive immunity

24.4 The immune response counters specificinvaders

SPECIFIC IMMUNITY

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Key Characteristics

The immune response involves specializedwhite blood cells called lymphocytes

The immune system: lymphocytes, thechemicals they produce, and the organs thatthey live in

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24 5 Lymphocytes mount a dual defense

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Two kinds of

lymphocytes carryout the specificimmune response

B cells secreteantibodies thatattack antigens

T cells attack cellsinfected withpathogens

24.5 Lymphocytes mount a dual defense

Figure 24.5

BONE MARROW

Stem cell

Immature

lymphocytes

Viablood

Antigenreceptors

B cellHUMORAL

IMMUNITYCELL-

MEDIATEDIMMUNITY

T cell

THYMUS

Viablood

OTHER PARTSOF THE

LYMPHATICSYSTEM

Lymph nodes,spleen, and otherlymphatic organs Final

maturation ofB and T cellsin lymphaticorgan

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An immune response has three steps

First: recognizing an invader

Second: launching an attack

Third: remembering specificinvaders to ward off futureinfections

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Step 1: Recognizing an Invader

Foreign invaders exhibit characteristicantigens

Foreign molecules that are particular to aninvading microbe or toxin

Immune cells respond to the presence of

antigens

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Antibodies and T-cell Receptors

Antibodies and T-cell receptors recognizeand bind to foreign antigens

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Antibodies

Antibodies are proteins that can beattached to B cells or free-floating in theblood

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Antibodies

Antibodies

Y-shaped molecules made of light peptide

chains and heavy peptide chains

Both chains have constant andvariableregions that form highly specific antigen

binding sites Each type of antibody is unique to the B cell

that makes them

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24 10 Antibodies are the weapons of humoral

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An antibody molecule

24.10 Antibodies are the weapons of humoralimmunity

Figure 24.10A

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Antibodies

There are five different classes of antibodies,which perform various functions

Inactivate their antigens by binding them andcausing them to clump together

Assist white blood cells to engulf microbes

Activate natural killer cells

Bind to blood proteins of the complementsystem

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Antibodies

Some classes of antibodies can cross theplacenta and provide immunity to adeveloping child

Another class is secreted in breast milk

Both help the newborn, whose immune

system is not fully developed

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24 6 Antigens have specific regions where

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Antigenicdeterminants(epitopes) arethe molecules

to whichantibodies bind

24.6 Antigens have specific regions whereantibodies bind to them

Figure 24.6

Antibody Amolecules

Antigen

Antibody Bmolecule

Antigenicdeterminants

Antigen-bindingsites

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Immune Cells Launch an Attack

Once an invading antigen has been detected,two forms of attack occur

Humoral immunity

Cell-mediated immunity

24.7 Clonal selection musters defensive forces

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When an antigen enters the body, it activatesonly lymphocytes with complementaryreceptors

B and T cells multiply into clones of specializedeffector cells that defend against the triggeringantigen

This is called clonal selection

24.7 Clonal selection musters defensive forcesagainst specific antigens

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Humoral Immunity

Provided by B cells and circulatingantibodies

Attack antigens circulating in thebloodstream and lymph

Each B cell has a unique antibody attached to

its surface that will only bind with properlyshaped antigens

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Humoral Immunity

The mechanism of humoral immunityoccurs in the following series of steps

1. Attached B cell antibodies bind to an invadingantigen in the blood

2. Bound B cell divides rapidly forming many

identical copies (clonal selection)3. B cell clones differentiate to form memory B

cells and plasma cells

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Figure 24.7

Antigen molecules

Variety ofB cells in a

lymph node

Cell growthdivision, anddifferentiation

Clone of manyeffector cellssecretingantibodies

Antibodymolecules

Antigen receptor(antibody oncell surface)

Endoplasmicreticulum

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Humoral Immunity

Memory B cells: saved to fight futureinfection

Plasma cells: mass-produce the specificantibody into the blood

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24.11 Antibodies mark antigens for elimination

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Antibodies may

block harmful antigens on microbes

clump bacteria or viruses together

precipitate dissolved antigens

activate complement proteins

g

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Figure 24.11

Binding of antibodies to antigensinactivates antigens by

Neutralization

(blocks viral binding sites;coats bacterial toxins)

Agglutination

of microbes

Precipitation of

dissolved antigensActivation

of complement

Virus

Bacterium

Bacteria

Antigen

molecules

Complementmolecule

Foreign cell Hole

Enhances

Phagocytosis

Macrophage

Cell lysis

Leads to

24.8 The initial immune response results in a type

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In the primary immune response, clonalselection produces memory cells

These cells may confer lifelong immunity

p ypof memory

Figure 24.8A

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When memorycells are activated

by subsequentexposure to anantigen, theymount a morerapid andmassivesecondary

immune response

Figure 24.8B

Unstimulated lymphocyteFirst exposure to antigen

FIRST CLONE

Memory cellsEffector cellsSecond exposure to antigen

SECOND CLONE

More memory cellsNew effector cells

24.9 Overview: B cells are the main warriors of

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Triggered by a specific antigen, a B celldifferentiates into an effector cell

The effector cell is called a plasma cell

The plasma cell secretes antibodies

humoral immunity

PRIMARY RESPONSE(i iti l t

Antigen

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Figure 24.9

(initial encounterwith antigen) Antigen receptor

on a B cell

Antigen bindingto a B cell

Memory B cell

Antibodymolecules

Plasma cell

Cell growth,

division, anddifferentiation

SECONDARY RESPONSE(can be years later)

Cell growth,division, and furtherdifferentiation

Larger cloneof cells

Plasma cell

Antibodymolecules

Laterexposureto sameantigen

Memory B cell

Clone ofcells

24.12 Connection: Monoclonal antibodies are

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These molecules areproduced by fusingB cells specific for asingle antigenic

determinant witheasy-to-grow tumorcells

powerful tools in the lab and clinic

Figure 24.12A

Antigen injectedinto mouse

Tumor cells grownin culture

B cells

(from spleen)Tumor cells

Cells fused togenerate hybridcells

Single hybrid cellgrown in culture

Antibody

Hybrid cell culture,producing monoclonal antibodies

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These cells are usefulin medical diagnosis

Example: homepregnancy tests

They are also usefulin the treatment ofcertain cancers

Figure 24.12B

24.13 T cells mount the cell-mediated defense and

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Provided by T cells, which attack cancer cellsand cells that have been invaded by viruses

Three types of T cells are involved

Helper T cells

Cytotoxic T cells

Memory T cells

aid humoral immunity

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Cell-Mediated Immunity

Helper T cells

Bind to antigens presented by a

macrophage that consumed them

Cell mediated immunity

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Cell-mediated immunity

An antigen-

presenting cell(APC) firstdisplays aforeign antigen

and one of thebodys own selfproteins to ahelper T cell

Figure 24.13A

1

2 3

4

Microbe

Macrophage(will become APC)

Antigen from microbe(nonself molecule)

Self protein

Self proteindisplayingantigen T cell receptor

Bindingsite for

selfprotein

HelperT cell

Binding sitefor antigenAPC

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Helper T cells

Produce cytokines that stimulate T cell

division and differentiationWill form memory T cells and cytotoxic

T cells

Will also stimulate division of B cells(humoral response) that are bound to anantigen

The helper T cells receptors recognize the self-

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The helper T cell s receptors recognize the selfnonself complexes on the APC

The interaction activates the helper T cells

The helper T cell can then activate cytotoxic Tcells with the same receptors

Figure 24.13B

Self proteindisplayingan antigen

T cellreceptor

Interleukin-2stimulatescell division

CytotoxicT cell

Interleukin-2activates

other T cellsand B cells

Cell-mediatedimmunity(attack oninfected cells)

Humoralimmunity(secretion ofantibodies byplasma cells)

B cell

HelperT cell

APC

Interleukin-1activateshelper T cell

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Cytotoxic T cells

Bind directly to cancerous or virally-infected

cells Release proteins that poke holes in

cancer/infected cell membrane, killing thecell


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Cytotoxic T cells bind to infected body cells and

destroy them

Figure 24.13C

Cytotoxic T cell bindsto infected cell1 2 3Perforin makes holesin infected cells membrane Infected cell is destroyed

INFECTED CELL

Perforinmolecule

CytotoxicT cell

Foreignantigen

Holeforming

y

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Memory T cells

Dormant helper T cells that fight future

infection by the antigen that produced it

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24.14 Cytotoxic T cells may help prevent cancer

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Cytotoxic T cells may

attack cancer cells

The surface moleculesof cancer cells are

altered by the disease

Figure 24.14

24.15 The immune system depends on ourl l fi i t

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The immune system normally reacts onlyagainst nonself substances

It generally rejects transplanted organs

The cells of transplanted organs lack therecipients unique fingerprint of self proteins

molecular fingerprints

DISORDERS OF THE IMMUNE SYSTEM

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Autoimmune diseases

The system turns against the bodys ownmolecules

Immunodeficiency diseases

Immune components are lacking, and infections

recur Physical and emotional stress may weaken the

immune system

24.16 Connection: Malfunction or failure of theimmune system causes disease

24.17 Connection: Allergies are overreactions tot i i t l ti

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Allergies are abnormal sensitivities toallergens in the surroundings

certain environmental antigens

Figure 24.17

Allergen(pollen grain)

B cells makeantibodies

Antigenicdeterminant

SENSITIZATION: Initial exposure to allergen

Antibodiesattach tomast cell

B cell(plasma cell)

Histamine

Mastcell

Allergen binds toantibodies onmast cell

Histamine isreleased, causingallergy symptoms

LATER EXPOSURE TO SAME ALLERGEN

24.18 Connection: AIDS leaves the bodyd f l

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The AIDS virus attacks helper T Cells This cripples both cell-mediated and humoral

immunity

So far, AIDS is incurable

Drugs and vaccines offer hope for the future

Practicing safer sex could save many lives

defenseless

Documents

Ch 24 Immune Hb 2008