Immune system
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Immune System. Animals have various means of defense against pathogens —agents that cause disease. Defense systems are based on the recognition of self (one’s own) and nonself (foreign) molecules. Two general types of defense mechanisms:

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Immune System

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Immune system

Immune System

Animals have various means of defense against pathogens—agents that cause disease.

Defense systems are based on the recognition of self (one’s own) and nonself (foreign) molecules.


Immune system

Two general types of defense mechanisms:

Nonspecific defenses: protect against anything & everything (aka Innate)

Specific defenses: aimed at specific pathogens (aka Adaptive)


Immune system

Non-Specific Immunity

Barriers: skin

mucous membranes

cilia & mucus

normal flora

phagocytosis by macrophages

inflammation


Immune system

Blood

plasma + RBCs + WBCs + platelets

transport for both non-specific and specific

Lymph

derived from blood;

returns fluid from tissue

to circulation

nodes- cells of the

immune system

reside here and

check fluid for pathogens


Immune system

Red and white blood cells originate from pluripotent stem cells in the bone marrow.

These cells constantly divide and can differentiate into a variety of blood cells.


Immune system

http://www.youtube.com/watch?v=I_xh-bkiv_c&feature=related


Immune system

Specific Immunity

Antibodies are proteins that bind to substances identified as nonself. Secreted by B cells.

T cell receptors are integral membrane proteins, recognize and bind nonself molecules on other cells.

Major histocompatibility complex (MHC): on the surface of most mammalian cells. They are self-identifying labels.

Antigens: protein or part of protein-flag = not me


Immune system

T cell receptors and antibodies bind to specific nonself molecules (antigens).

Specific sites on the antigens are called antigenic determinants or epitopes.


Immune system

  • The specific immune system has four key traits:

  • Specificity

  • Diversity—response to a wide variety of pathogens

  • Ability to distinguish self from nonself

  • Memory


Humoral vs cellular response

Humoral vs. Cellular Response

Antibody reacts to Antigen in

blood, lymph & tissue fluids

Triggers B cells to clone itself

plasma cells make Antibody that binds to pathogen

memory cells-perpetuate clone & reduce response time at 2nd exposure

T cell receptor recognizes

Antigen + MHC (me signal)

Triggers T cells to clone itself

T-cytotoxic –destroys cells with MHC1 + antigen

T-helper-alerted by MHC2 + antigen-stimulates B cells to proliferate

T-suppressor-turn off response


Figure 24 7a

Figure 24.7A

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Primary immune response

Secondary immune response

Antigenmolecules

Antibodymolecules

Antigen receptoron the cellsurface

B cells withdifferentantigenreceptors

First exposureto the antigen

Cell activation:growth, division,and differentiation

Clone of plasma (effector) cellssecreting antibodies

Antigenmolecules

Second clone

Antibodymolecules

Second exposureto the same antigen

First clone

Endoplasmicreticulum

Clone of memory cells

Memory cells

Plasma (effector) cells secreting antibodies


Figure 24 7a s1

Figure 24.7A_s1

1

Primary immune response

Antigen receptoron the cellsurface

B cells withdifferentantigenreceptors


Figure 24 7a s2

Figure 24.7A_s2

1

2

Primary immune response

Antigenmolecules

Antigen receptoron the cellsurface

B cells withdifferentantigenreceptors


Figure 24 7a s3

Figure 24.7A_s3

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2

3

Primary immune response

Antigenmolecules

Antigen receptoron the cellsurface

B cells withdifferentantigenreceptors

First exposureto the antigen

Cell activation:growth, division,and differentiation


Figure 24 7a s4

Figure 24.7A_s4

1

2

3

4

5

Primary immune response

Antigenmolecules

Antigen receptoron the cellsurface

B cells withdifferentantigenreceptors

First exposureto the antigen

Cell activation:growth, division,and differentiation

Antibodymolecules

First clone

Endoplasmicreticulum

Plasma (effector) cells secreting antibodies

Memory cells


Figure 24 7a s5

Figure 24.7A_s5

6

Antigenmolecules

Second exposureto the same antigen

Memory cells


Figure 24 7a s6

Figure 24.7A_s6

6

Secondary immune response

Antibodymolecules

Antigenmolecules

Clone of plasma (effector) cellssecreting antibodies

Second exposureto the same antigen

Second clone

Clone of memory cells

Memory cells


Figure 24 7b

Figure 24.7B

Second exposureto antigen X,first exposureto antigen Y

Secondary immuneresponse toantigen X

First exposure to antigen X

Antibody concentration

Primary immuneresponse toantigen X

Primary immuneresponse toantigen Y

Antibodiesto Y

Antibodiesto X

56

0

14

35

42

7

21

28

49

Time (days)


Figure 24 9

Figure 24.9

Binding of antibodies to antigensinactivates antigens by

Neutralization(blocks viral binding sites;coats bacteria)

Precipitation ofdissolved antigens

Activation of thecomplement system

Agglutinationof microbes

Complementmolecule

Bacteria

Virus

Antigenmolecules

Bacterium

Foreign cell

Hole

Leads to

Enhances

Phagocytosis

Cell lysis

Macrophage


Humoral vs cellular response1

Humoral vs. Cellular Response

Antibody reacts to Antigen in

blood, lymph & tissue fluids

Triggers B cells to clone itself

plasma cells make Antibody that binds to pathogen

memory cells-perpetuate clone & reduce response time at 2nd exposure

T cell receptor recognizes

Antigen + MHC (me signal)

Triggers T cells to clone itself

T-cytotoxic –destroys cells with MHC1 + antigen

T-helper-alerted by MHC2 + antigen-stimulates B cells to proliferate

T-suppressor-turn off response


Figure 24 11

Figure 24.11

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5

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2

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1

Humoralimmune response(secretion ofantibodies byplasma cells)

Phagocytic cell(yellow) engulfinga foreign cell

B cell

Self-nonselfcomplex

Interleukin-2stimulatescell division

T cellreceptor

Macrophage

Microbe

Interleukin-2activates B cellsand other T cells

HelperT cell

Cell-mediatedimmune response(attack oninfected cells)

Self protein

Bindingsite for theself protein

CytotoxicT cell

Antigen-presentingcell

Interleukin-1stimulates thehelper T cell

Antigen from the microbe(nonself molecule)

Bindingsite for theantigen


Figure 24 11 1

Figure 24.11_1

3

2

1

Self-nonselfcomplex

Macrophage

Microbe

Self protein

Antigen-presentingcell

Antigen from the microbe(nonself molecule)


Figure 24 11 2

Figure 24.11_2

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2

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Self-nonselfcomplex

B cell

Interleukin-2stimulatescell division

T cellreceptor

Interleukin-2activates B cellsand other T cells

HelperT cell

Bindingsite for theself protein

CytotoxicT cell

Antigen-presentingcell

Interleukin-1stimulates thehelper T cell

Bindingsite for theantigen


Figure 24 12 s1

Figure 24.12_s1

1

A cytotoxic T cell bindsto an infected cell.

Self-nonselfcomplex

Foreignantigen

Infected cell

CytotoxicT cell

Perforinmolecule


Figure 24 12 s2

Figure 24.12_s2

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1

Perforin makes holes in theinfected cell’s membrane,and an enzyme thatpromotes apoptosis enters.

A cytotoxic T cell bindsto an infected cell.

Self-nonselfcomplex

A hole forming

Foreignantigen

Infected cell

Enzymes thatpromote apoptosis

CytotoxicT cell

Perforinmolecule


Figure 24 12 s3

Figure 24.12_s3

3

2

1

Perforin makes holes in theinfected cell’s membrane,and an enzyme thatpromotes apoptosis enters.

The infected cellis destroyed.

A cytotoxic T cell bindsto an infected cell.

Self-nonselfcomplex

A hole forming

Foreignantigen

Infected cell

Enzymes thatpromote apoptosis

CytotoxicT cell

Perforinmolecule


Problems

Problems

  • Allergy-hypersensitive immune repsonse

    • stimulates release of histamine b/c of antigen-antibody interaction (immediate response)

    • T cell response initiated (delayed response)

  • Autoimmune

    • fail to destroy antibody producing cell that matches to self antigens

    • virus antigen resembles self antigen

    • T cells recognize antigen (non-self) that has a portion similar to self antigen


Figure 24 17

Figure 24.17

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Sensitization: Initial exposure to an allergen

Later exposure to the same allergen

B cell(plasma cell)

Mastcell

Antigenic determinant

Histamine

B cells makeantibodies.

The allergen bindsto antibodies ona mast cell.

Antibodiesattach to amast cell.

Histamine isreleased, causingallergy symptoms.

An allergen (pollengrain) enters thebloodstream.


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