the immune system chapter 24 - davis school · pdf filefight infections copyright © 2005...

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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

The Immune System

Chapter 24

Bacteria


An AIDS Uproar• Acquired immune deficiency syndrome (AIDS)

– Is epidemic throughout much of the world

• Thousands of people are infected every day


• HIV, the virus that causes AIDS, attacks the immune system

– And eventually destroys the body’s ability to fight infection

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INNATE DEFENSES AGAINST INFECTION

24.1

• Innate immunity

– Is present and effective long before exposure to pathogens

– Innate defenses against infection

• Surface barriers

– skin

– mucous membranes

• Nonspecific response

– phagocytic cells

– antimicrobial proteins


• Microbes that breach the body’s external defenses

– Are engulfed and destroyed by macrophages

Figure 24.1A

Bacteria


New viruses

��Host cell 1Makes interferon; is killed by virus

4��Host cell 2

Protected against virus by interferon from cell 1

• Interferons are proteins produced by virus-infected cells

– That help other cells resist viruses

2 Interferon genesturnedon

mRNA

3

Interferon molecules

DNA

1

Viral nucleic acidAntiviral proteins block viral reproduction

Interferon stimulates cell to turn on genes for antiviral proteins

5

Figure 24.1B

3


Complement system

Group of 30 plasma proteins

• Circulate in blood

• Trigger lysis of invading cells

• Help trigger specific and nonspecific immune response



DEFENSE MECHANISMS

4


White blood cell role in the inflammatory response

Neutrophils:

phagocytize bacteria

Eosinophils:

secrete enzymes that punch holes in bacteria

Basophils:

Secretes histamine

Macrophages:

engulf and digest most any antigens


24.2 The inflammatory response mobilizes nonspecific defense forces

• Tissue damage triggers the inflammatory response

Pin�� Skin surface

Bacteria

Chemical signals

White blood cell

1 Tissue injury; release of chemical signals such as histamine

2 Dilation and increased leakiness of local blood vessels; migration of phagocytes to the area

3 Phagocytes (macrophages and neutrophils) consume bacteria and cell debris; tissue heals

Swelling

Phagocytes and fluid move into area

Phagocytes

Blood vessel

Figure 24.2


• The inflammatory response

– Can disinfect tissues and limit further infection

– Localized warming and redness occurs

– Macrophages secrete interleukins• Communication w/other WBCs

• Signal fever

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24.3 The lymphatic system Is a network of lymphatic vessels and organs

Figure 24.3

Adenoid

Tonsil

Lymph nodes

Right lymphatic duct, entering vein

Thymus

Appendix

Thoracic duct

Bone marrow

Lymphatic vessels

Spleen

Thoracic duct, entering vein

Lymph node

Masses of lymphocytes and macrophages

Valve

Lymphatic vessel

Blood capillary

Tissue cells

Interstitial fluid

Lymphatic capillary


• Vessels collect fluid from body tissues– return it as lymph to the blood

• spleen and lymph nodes– Are packed with white blood cells that

fight infections


Adenoid

Tonsil

Lymph nodes

Right lymphatic duct, entering vein

Thymus

Appendix

Thoracic duct

Bone marrow

Lymphatic vessels

Spleen

Thoracic duct, entering vein

Lymph node

Masses of lymphocytes and macrophages

Valve

Lymphatic vessel

Blood capillary

Tissue cells

Interstitial fluid

Lymphatic capillary

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24.4 The immune response counters specific invaders

• Immune system – Responds to antigens

• Any molecule that causes an immune response

– And “remembers” antigen as an invader• Chicken pox

ACQUIRED IMMUNITY: develops after exposure to pathogen


Active immunity:

• own immune system produces antibodies

– Infection or vaccination

Passive immunity

• receive “premade” antibodies

– Triggers active immunity

Figure 24.4


24.5 Lymphocytes carry out immune responseTwo kinds of lymphocytes

– B cells secrete antibodies that attack antigens– T cells attack cells infected with pathogens

Bone marrow Thymus

Stem cell

Immature lymphocyte

B cellHumoral immunity

Via blood

Antigenreceptors

Via blood

T cellCell-mediated immunity

Lymph nodes, spleen, and other lymphatic organs

Final maturation of B and T cells in lymphatic organ

Other parts of the lymphatic system

Figure 24.5A

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• Millions of kinds of B cells and T cells, each with different membrane receptors

– Wait in the lymphatic system, where they may respond to invaders

– Dual Defense• Humoral immunity

– Against bacteria and viruses free in the blood or interstitial fluid

– B cells• Cell-mediated

– Against bacteria and viruses inside body cells, fungi, protozoans, and cancer cells

– T cellsFigure 24.5B


24.7 Clonal selection

•PRIMARY IMMUNE RESPONSE

• First time against a specific antigen

– antigen enters the body

– It activates a small subset of lymphocytes with specific receptors to that antigen

– Activated lymphocyte cells multiply into clones


Clonal Selection• The primary immune response, produces

– effector cells• Combat the antigen, short lived

– memory cells• lifelong immunity

• In the secondary immune response– Second exposure to antigen

• Memory cells activited

• Faster response

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• The primary and secondary immune responses

Primary immuneresponse

B cells with differentresponse

Cell activation:growth, division,and differentiation

Antibodymolecules

Plasma (effector) cells secreting antibodies

Endoplasmicreticulum

Clone of memory cells

Antigen receptor(antibody on cellsurface)

Antigenmolecules

2

First exposureantigen

3

4

1

5

5

Antigenmolecules

6 Second exposureto same antigen

Antibodymolecules

Endoplasmicreticulum

Plasma (effector) cells secreting antibodies Clone of memory cells

Secondary immuneresponse

Figure 24.7A


Second exposure to antigen X, first

exposure to antigen Y

First exposure to antigen X

Primary immune response to antigen X

Primary immune response to antigen Y

Antibodies to Y

Antibodies to X

Ant

ibod

y co

ncen

tratio

n

0 7 14 21 28 35 42 49 56

Time (days)

Secondary immune response to antigen

X

Figure 24.7B

Primary vs. Secondary Immune Response• The primary immune response

– Is slower than the secondary immune response


24.8 Antibodies are the weapons of humoral immunity

• Antibody molecules

– Produced by effector B cells

• Bind to antigen

• Assist in elimination of antigen

Figure 24.8A

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• An antibody molecule

– Specific antigen-binding

Figure 24.8B

Light chain

Heavy chain

CC

Antigen-binding sites


Antibody elimination mechanismsNeutralization

physically blocks harmful antigens

Agglutination

clumps groups of cells together for phagocytosis

Precipitation of dissolved antigens

link dissolved antigen molecules together

Activates complement proteins

attach to foreign cells causing lysis


Binding of antibodies to antigens inactivates antigens by

Neutralization(blocks viral binding sites;

coats bacteria) Agglutination of microbes

Precipitation of dissolved antigens

Activation of Complement system

Cell IysisPhagocytosis

Virus

Bacterium

Bacteria

Antigen molecules

Complement molecule

Foreign cell Hole

Macrophage

Enhances Leads to

24.9 Antibodies mark antigens for elimination

Figure 24.9

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24.11 Helper T cells stimulate humoral and cell-mediated immunity

1. Macrophage ingests a microbe

2. Macrophage becomes antigen presenting cell by placing part of the antigen on its membrane by its MHC

3. Helper T cell recognize and bind to the self-nonself complex on the antigen presenting cell

• Receptors on each helper T cell can bind only ONE kind of self-nonself complex on the antigen presenting cell


Humoral Immunity

B cells divide

Memory B cells

Effector B cells

-Make antibodies

VS Cell-Mediated Response

Cytotoxic T cells Divide

Memory T cells

active cytotoxic T cells

-target infected body cells

4. Antigen presenting cell releases interleukin-1●stimulates the helper T cell

5. Activated helper T cells ●Divide to produce memory and

more helper T cells●Secrete interleukin-2 which

activates B cells and Cytotoxic T cells

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Figure 24.11

MicrobeMacrophage

Antigen from microbe (nonself molecule)

1

Self protein

23

4

5 6

7

Antigen-presenting cell

Interleukin-1 stimulates helper T cell

HelperT cell

Interleukin-2stimulatescell division

Interleukin-2activatesother B cells and T cells

HumoralImmunity(secretion of antibodies by plasma cells)

Cytotoxic T cell

Cell-mediated immunity (attack on infected cells)

Binding site for antigen

Binding site for self protein

B cellSelf-nonselfcomplex T cell

receptor



Humoral Immunity

(Antibody mediated response)

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24.12 HIV destroys helper T cells, compromising the body’s defenses

• The AIDS virus attacks helper T Cells

– Opening the way for opportunistic infection

CONNECTION

Figure 24.12


3 Infected cellis destroyed

1 Cytotoxic T cell bindsto infected cell

2 Perforin makes holes ininfected cell’s membraneand enzyme entersSelf-nonself

complex

Infecte cell

CytotoxicT cell

Perforinmolecule

Foreignantigen

Enzyme thatcan promoteapoptosis

Holeforming

Figure 24.13

24.13 Cell Mediated Response

– Cytotoxic T

• Bind to infected body cells and destroy them

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24.14 Cytotoxic T cells may help prevent cancer

• Cytotoxic T cells may attack cancer cells

– Which have abnormal surface molecules

Figure 24.14


24.15 The immune system depends on our molecular fingerprints

• The immune system

– Normally reacts only against nonself substances, not against self

– May reject transplanted organs because these cells lack the unique “fingerprint” of the recipient’s self proteins

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DISORDERS OF THE IMMUNE SYSTEM CONNECTION24.16 Malfunction or failure of the immune system causes

disease

• In autoimmune diseases

– The system turns against the body’s own molecules

• In immunodeficiency diseases

– Immune components are lacking, and frequent infections recur

• Physical and emotional stress

– May weaken the immune system


24.17 Allergies are overreactions to certain environmental antigens

• Allergies

– Are abnormal sensitivities to antigens (allergens) in the surroundings

CONNECTION


• The two stages of an allergic reaction

Figure 24.17

B cell(plasma cell)

Antigenic determinant

1 Allergen (pollen grain)enters blood stream

2 B cells makeantibodies

3 Antibodiesattach tomast cell

Sensitization: Initial exposure to allergen

Mast cell

Histamine

4 Allergen binds toantibodies onmast cell

5 Histamine isreleased, causingallergy symptoms

Later exposure to same allergen

3 Antibodiesattach tomast cell

the immune system chapter 24 - davis school · pdf filefight infections copyright © 2005...

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