Macrophage Activation & Cytokine Release

Dendritic Cells & Antigen Presentation

Neutrophils – Polymorphonuclear cells (PMNs) are

recruited to the site of infection where they phagocytose invading organisms and kill them

intracellularly. In addition, PMNs contribute to collateral tissue

damage that occurs during inflammation.

Neutrophils & Innate Defense

Antigen Presenting Cells (APCs)

Vascular Permeability

The production of increased vascular permeability during inflammation. The

presence of prostaglandins, leukotrienes, and histamine causes cells lining venules to pull apart, allowing phagocytes to leave the bloodstream and more easily reach

a site of infection. The leakage of fluid and cells causes the edema and pain associated with inflammation.

© 2008 Pearson Education, Inc., publishing as Benjamin Cummings

An Overview of Inflammation

© 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Production of fever in response to infection

© 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innate Immune Response

! "Antigen-presenting cells (APCs) are

activated through pathogen-associated

molecular pattern (or PAMPs) by

receptors such as TLRs.

! "This activation leads to the production of

inflammatory cytokines and the

expression of co-stimulatory molecules on

the cell surface.

Pattern recognition receptors - PRRs

Mammalian TLR family members & their respective ligands

Interplay of Innate & Adaptive Immune Systems

http://content.nejm.org/cgi/content/full/343/5/338/F3

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Lecture 3: B Cells and AntibodiesLecture 3: B Cells and Antibodies

*FIRST - Finish up on Innate Immunity:

Complement System

Michele Klingbeil

*FIRST - Finish up on Innate Immunity:

Complement System

Michele Klingbeil

2

Lecture Objectives - Complement

• Understand different pathways of C activation

• Know complement proteins (nomenclature)

• Know the enzymatic and non-enzymatic

mechanisms of complement activation

3

Complement Functions

Historically, complement referred to a heat-labile

serum component that could lyse bacteria

• Host benefit:

– opsonization to enhance phagocytosis

– phagocyte attraction and activation

– lysis of bacteria and infected cells

– regulation of antibody responses

– clearance of immune complexes

– clearance of apoptotic cells

• Host detriment:

– Inflammation, anaphylaxis

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4

Complement Pathways

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The Complement System

• More than 20 serum

proteins involved

• Some components

bind to antibody

• Some components

bind to membranes

• Zymogen cleavage

cascade - activation

• C3 most important -

most abundant!

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Classical Complement Pathway

3

7

Classical Complement Pathway

See animations

at website

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Mannose Binding Lectin Pathway

Mannose containing Polysaccharides

Similar to Classical Pathway

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The Membrane Attack Complex

4

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Terminal Pathway (Lytic Attack)

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Regulatory Proteins of Complement Pathways

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Natural Killer Cells

• Lymphocyte lineage

• Normal cells are not killed

because inhibitory signals

from MHC class I molecules

override activating signals

• In tumor cells or virus-infected

cells, reduced expression or

alteration of MHC molecules

interrupts the inhibitory

signals, allowing activation of

NK cells and lysis of target

cells.

Bone marrow

5

13

Natural Killer Cells

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Innate Immunity to Viral Infections

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Timing of innate immunity after infection

Barriers - Seconds

Epithelial activation - Minutes

Cytokines/chemokines -

Minutes to days

Neutrophils -

Hours

Monocytes/macrophages - Hours to days

NK cells - Hours to days

Short-lived Long-lived & connect with

adaptive immune system

Complement - Minutes

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Summary of Immune Response

Immune

System

Innate(Nonspecific)

1o line of defense

Adaptive(Specific)

2o line of defense

Protects/re-exposure

Cellular

Components

Humoral

Components

Cellular

Components

Humoral

Components

Anatomical

Barriers

Adaptive(Specific)

2o line of defense

Protects/re-exposure

Humoral

Components

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Lecture Objectives: B Cells & Antibodies

• Discuss the general properties of all immunoglobulins

• Describe the basic structure of immunoglobulins

• Relate immunoglobulin structure with function

• Define immunoglobulin hypervariable and framework

regions

• Define immunoglobulin classes and subclasses

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Adaptive Immunity

Immunity established to adapt to infection

• Learnt by experience

• Confers pathogen-specific immunity

• Enhanced by second exposure

• Has memory

• Uses cellular and humoral components

• Is poorly effective without innate immunity

Antibodies reflect infections to which an individual has been exposed:

diagnostic for infection

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B Cell Maturation & VDJ Rearrangement

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Immunoglobulin Diversity

When a stem cell changes to become a B cell, DNA

segments for both heavy (VDJ) and light (VJ)

Immunoglobulin chains are randomly combined.

Each B cell ends up with functional genes for making

one light and one heavy chain coding for an antibody as

a membrane-bound receptor

Antibody specificity depends on the gene fragments

used.

Antibodies are produced that can react with almost any

chemical structure in nature, including our own proteins

Imprecise recombination and mutation increase the

variability into billions of possible combinations

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Immunoglobulin (Antibody) Structure

The basic IgG Ab molecule has aMW of ~150kDa

These Abs have a basic structure of4 peptide chains

There are 2 identical light (L) chains~25kDa

There are also 2 identical heavy (H)chains, polypeptides of ~50kDa

Each L chain is bound to a H chainby a –S-S- and non-covalentinteractions (salt linkages, hydrogenbonds and hydrophobic bondsforming a heterodimer

Similar –S-S- and non-covalentinteractions link the identical H-Lcombinations together to form acomplete molecule, a dimer ofdimers

8

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Immunoglobulin Fragments

Ag

Binding

Complement Binding Site

Placental

Transfer

Binding to Fc

Receptors

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Immunoglobulin regions

Heavy & Light ChainsDisulfide bondsInter-chain

Intra-chain

Variable & ConstantRegions

–VL & CL

–VH & CH

Hinge Region

CH1

VL

CL

VH

CH2 CH3

Hinge Region

Carbohydrate

Disulfide bond

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Antibodies and Epitopes

9

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B Cell Response to Antigen

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B Cell Receptor

2 major parts• External Immunoglobulin

• Specificty for antigen

• Short cytoplasmic tail - no

direct signaling

• Internal Ig!/Ig" dimer -

cytoplasmic tail for intracellular

signaling

• Responder to what mIg “sees”.

• Other important components

(not essential for exam)

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B Cell Receptor - Additional Complexity

CD21

(C3d receptor)

CD19

CD81

(TAPA-1)

Ig!Ig"

CD45

The B cell co-receptor

10

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B Cell Receptor Complex Signaling

Concept of complex signaling pathways involved:

Do not try to memorize all these pathways!

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Antibody Isotypes

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Ig Isotype Functions

11

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Ig Isotype Distribution

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Cytokine Regulation of Ig Isotypes

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Humoral Immune Response

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Amazing Immunoglobin Diversity