1. pathogens (such as bacteria, fungi, and viruses) innate immunity (all animals) rapid response...

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Pathogens(such as bacteria,fungi, and viruses)

INNATE IMMUNITY(all animals)

• Rapid response

Recognition of traits sharedby broad ranges ofpathogens, using a smallset of receptors

•

Recognition of traits specific to particularpathogens, using a vastarray of receptors

•

• Slower response

Barrier defenses:SkinMucous membranesSecretions

Internal defenses:Phagocytic cellsNatural killer cellsAntimicrobial proteinsInflammatory response

Humoral response:Antibodies defend againstinfection in body fluids.

Cell-mediated response:Cytotoxic cells defendagainst infection in body cells.

ADAPTIVE IMMUNITY(vertebrates only)

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Pathogen

PHAGOCYTICCELL

VacuoleLysosomecontainingenzymes

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Thymus

Peyer’spatches(smallintestine)

Appendix(cecum)

AdenoidTonsils

Lymphaticvessels

Spleen

Lymphnodes

Lymphnode

Bloodcapillary

Interstitialfluid

Tissuecells

Lymphatic vessel

Lymphatic vessel

Masses ofdefensive cells

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Pathogen Splinter

Mastcell

Macro-phage

Capillary

Redblood cells

Neutrophil

Signalingmolecules

Movementof fluid

Phagocytosis

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Antigen receptors

Mature B cell Mature T cell

7Cytoplasm of B cell

Antigen-binding site

B cellantigenreceptor

B cell

Lightchain

Disulfidebridge

Antigen-binding site

Variable regions

Constant regions

Transmembraneregion

Heavy chains

Plasmamembrane

C C

C C

V

V

V

V

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AntibodyAntigenreceptor

B cell

Antigen Epitope

Pathogen(a) B cell antigen receptors and antibodies

Antibody C

Antibody BAntibody A

Antigen

(b) Antigen receptor specificity

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T cellantigenreceptor

T cell Cytoplasm of T cell

Plasmamembrane

chain chain

Disulfidebridge

Antigen-bindingsite

Variableregions

Constantregions

Transmembraneregion

V V

C C

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Displayedantigenfragment

MHC molecule

Antigenfragment

Pathogen

Host cell

T cell

T cell antigenreceptor

(a) Antigen recognition by a T cell

(b) A closer look at antigen presentation

Antigen fragment

MHCmolecule

Host cell

Top view

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DNA ofundifferentiatedB cell

DNA ofdifferentiatedB cell

Recombination deletes DNA betweenrandomly selected V segment and J segment

Functional gene

Transcription

RNA processing

Translation

pre-mRNA

mRNA

Light-chain polypeptideAntigen receptor

B cellVariableregion

Constantregion

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3

4

1

Poly-A tailCap V39 J5

J5V39

V37 V38 V39

V37 V38 V39 V40

J5

J5J4J3J2J1

Intron

Intron

V C

C

C

C

C

C

C C

C

VVV

V

Intron

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AntigenAntigenreceptor

Antibody

Plasma cellsMemory cells

B cells thatdiffer inantigenspecificity

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Antigen-presentingcell

Pathogen

Antigen fragment

Class II MHC moleculeAccessory proteinAntigen receptor

Helper T cell

Cytokines

Humoralimmunity

Cell-mediatedimmunity

B cellCytotoxic T cell

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2

1

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Cytotoxic T cell

31 2

Accessoryprotein

Class I MHCmolecule

Infectedcell

Antigenreceptor

Antigenfragment

Perforin

Pore

Gran-zymes

ReleasedcytotoxicT cell

Dyinginfected cell

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Pathogen

31 2

Antigen-presentingcell Antigen

fragment

Class IIMHC

molecule

Antigenreceptor

Accessoryprotein

Helper T cell

B cell

Cytokines

Activatedhelper T cell

Memory B cells

Plasma cellsSecreted

antibodies

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OpsonizationNeutralization

Antibody

VirusBacterium

Macrophage

Activation of complement system and poreformation

Complement proteins

Formation of membraneattack complex

Flow of waterand ions

Pore

AntigenForeigncell

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IgE

Allergen

Histamine

Granule

Mast cell