Newcastle University Medical Education Society Immunology Presentation by Christopher Taylor

05/05/2011

Structure of this session • Normal immune response – What actually happens – Application to different types of infections

• Ways it can go wrong – Immunodeficiency – Hypersensitivity reactions – Autoimmunity

Created by Laura Watson ©

the basics

• We won’t have time to cover vaccinations, transplantation, HIV or infectious disease

Barrier Mechanisms

Immune System Anatomy

• Intrinsic epithelial barriers e.g. nasal passages, mouth, airway, lungs, gut

• Longitudinal flow of air/fluid • Movement of mucus by cilia in lungs • Acids: skin, saliva, gut • Antibacterial peptides: skin, lungs, gut • Normal flora: skin, gut, vagina

Cells of the Immune System

Granulocytes

Monocytes

neutrophils

monocytes  tissue macrophages

eosinophils basophils  tissue mast cells

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Cells of the Immune System

Cells of the Immune System Y

Lymphocytes Dendritic cells

plasma cell

 main antigen presenting cells

memory B cell

B cells z

CD4

CD8

CD25

T cells

memory T cell

NK cell

NK cells

TCR

!*@!

innate immunity 0-4hrs

The Immune Response

TCR

inflammatory response (C3a, C4a, C5a)

MHC I

4-IBB

4-IBBL

infected cell

synapse formation (cells touch) perforin, granzymes, granulysin

opsonisation of pathogens (C3b, C4b) MAC complex pathogen lysis (C5b-C9)

induction of apoptosis

APC MHC II

CHO

TCR

TLR MHC II

dendritic cell

pathogen

IFN-γ CD40L

T H0 CD4

PAMP PRR

TCR MHC II

B7 CD28 CD40L

NK cell NF-ΚB activation

↑↑ costimulatory molecules e.g. B7

CD40 IL-2 IL-4 IL-5

proinflammatory cytokine release IL-1 IL-6 IL-8 IL-12 TNFα

B cell CD19

humoral immunity T H2

fever

memory cell

plasma cell Y

neutralise toxins

neutrophil

antibodies IgM  IgG IgA IgE

increased capillary permeability  oedema and swelling

+++

↑↑ CRP

chemotaxis microcoagulation to prevent spread of infection

cell-mediated immunity T H1

CD40

TCR

MBL

 humoral immunity (antibodies)  cell mediated immunity (cytotoxic T cells)

TC CD8

CD28

+++

3) Antigen specific immune response

TC CD8

complement activation

NO MHC I

2) Antigen presentation in lymph nodes  activation of T helper cells

MHC I

+++

IL-2

1) Pathogen recognition by cells of the innate immune system e.g. dendritic cells  cytokine release  complement activation  phagocytosis and internalisation of antigens

inflammation 4-96hrs

opsonise pathogens activate complement activate effector cells

Innate Immunity

pathogen

•

First line of defence against infection

•

Rapid response (0-4 hours)

•

Non-specific

•

No memory

•

Three main components: 1) cellular response by phagocytes + NK cells 2) chemical response: cytokines and complement 3) inflammation (4-96hrs)

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NK cell

Phagocytes

NK cell

• Large granular lymphocytes that form part of the innate immune system

• Examples include: – dendritic cells – blood monocytes and tissue macrophages – neutrophils (not found in healthy tissue)

• No activation is required (unlike T cells) • Inhibited by MHC I (self cells)

• Recognise pathogen PAMPs with PRRs

– MHC I expression is often suppressed in virally infected or cancerous cells – NK cells are therefore important in viral immunity and tumour rejection

• Internalise and kill pathogens • Present antigens to immune system cells via MHC complexes

• Release toxic granules to induce apoptosis

• NFKB activation  inflammatory response

C O M P L E M E N T

Natural Killer Cells

Proinflammatory Cytokines

C O M P L E M E N T

• Small proteins released by immune cells in response to evidence of infection • Important examples include: – IL-1  fever, activates lymphocytes – IL-6  fever, acute phase proteins, activates lymphocytes and antibody production – IL-8 (CXCL8)  neutrophil chemotaxis – IL-12  activates NK cells and TH1 cells – TNF-α  ↑↑ vascular permeability

innate immunity 0-4hrs

Inflammation

inflammation 4-96hrs

complement activation inflammatory response (C3a, C4a, C5a)

• A local response induced by complement (C3a, C4a, C5a) and cytokine release

MBL

• Main features:

pathogen

opsonisation of pathogens (C3b, C4b) MAC complex pathogen lysis (C5b-C9)

CHO

– neutrophil chemotaxis  “cleans up” – microvascular coagulation induced by tissue damage  confines infection – ↑↑ vascular permeability  inflammatory cell infiltrate, oedema and swelling – vasodilation and ↑↑ blood flow  redness

TLR

dendritic cell PAMP PRR

NO MHC I

NK cell NF-ΚB activation

↑↑ costimulatory molecules e.g. B7

proinflammatory cytokine release IL-1 IL-6 IL-8 IL-12 TNFα

↑↑ CRP fever chemotaxis

microcoagulation to prevent spread of infection

increased capillary permeability  oedema and swelling

neutrophil

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… So what happens next? • The specific adaptive immune response needs activating • This is done via antigen presentation to the adaptive immune system • Dendritic cells travel to lymph nodes and present antigens to naïve T helper cells in the context of MHC II complexes • MHC restriction is very important

innate immunity 0-4hrs

T H0 CD4

CD4 T Cell Activation

T H0 CD4

• In order to be fully activated by their specific antigen, T helper cells also require a second signal from APCs • Dendritic cells are able to provide this • B7 proteins (CD80 or CD86) on dendritic cells bind to CD28 on T cell surfaces • This ensures the adaptive immune system is activated in a safe, controlled manner

inflammation 4-96hrs

Humoral Immunity

complement activation inflammatory response (C3a, C4a, C5a)

MBL CHO

MHC restriction

TLR

dendritic cell

pathogen

MHC II

TCR

TH0 CD4

PAMP PRR NO MHC I

B7 CD28 second signal

NK cell NF-ΚB activation

↑↑ costimulatory molecules e.g. B7 ↑↑ CRP

proinflammatory cytokine release IL-1 IL-6 IL-8 IL-12 TNFα

fever chemotaxis

microcoagulation to prevent spread of infection

increased capillary permeability  oedema and swelling

cell-mediated immunity T H1 humoral immunity T H2

• TH2  B cells and antibodies • Fights extracellular infections:  most bacteria  some viruses  fungi  protozoa e.g. Giardia  worms

opsonisation of pathogens (C3b, C4b) MAC complex pathogen lysis (C5b-C9)

B cell CD19

neutrophil

Antibodies: Structure

Antibodies: Isotypes

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Humoral Immunity

Antibodies: Diversity

• TH2 cells activate B cell differentiation

• Humans can generate around 10 billion different specific antibodies

– recognise antigen expressed on B cell surface – provide CD40 ligand second signal – release cytokines e.g. IL-2, IL-4, IL-5

• Several mechanisms produce variations: – – – – – –

• B cells begin to make antibodies

VDJ recombination by RAG proteins junctional diversity (imprecise VDJ joining) “looping out” and rejoining of gene segments N regions (random addition of nucleotides) class switching somatic hypermutation and affinity maturation

– IgM production  Ig class switching – clonal expansion of antigen-specific B cells – somatic hypermutation + affinity maturation

• Plasma cells produce highly antigen-specific antibodies and release them into the blood

Antibodies: Function

B Cell Memory

1) neutralisation of toxins

• After infection has been cleared, some B cells remain to provide memory

2) opsonisation of pathogens

• Affinity maturation means that only highly specific B cells are selected

3) activation of complement

• Immediate proliferation and production of specific antibody at next encounter • The number of surviving memory cells increases after each reinfection

4) activation of effector cells

innate immunity 0-4hrs

inflammation 4-96hrs

Cell-mediated Immunity

complement activation inflammatory response (C3a, C4a, C5a) opsonisation of pathogens (C3b, C4b) MAC complex pathogen lysis (C5b-C9)

cell-mediated immunity T H1

MBL CHO

TLR

dendritic cell

pathogen

MHC II

TCR

TH0 CD4

PAMP PRR NO MHC I

MHC II

CD40L

↑↑ costimulatory molecules e.g. B7

CD40 IL-2 IL-4 IL-5

proinflammatory cytokine release IL-1 IL-6 IL-8 IL-12 TNFα

memory cell

plasma cell Y Y

neutrophil

neutralise toxins

Y antibodies IgM  IgG IgA IgE

TH1  APCs and CD8 T cells Fights intracellular infections: – – – –

humoral immunity T H2

fever

increased capillary permeability  oedema and swelling

B cell CD19

↑↑ CRP

chemotaxis microcoagulation to prevent spread of infection

+++

NF-ΚB activation

•

TCR

B7 CD28

NK cell

•

some bacteria most viruses parasites e.g. P. falciparum protozoa

Two main components:

CD8

1) activation of APCs 2) CD8 T cell cytotoxic response

opsonise pathogens activate complement activate effector cells

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Activation of APCs

CD8

• TH1 cells activate infected APCs using:

• Immunological synapse (cells touch) – release of perforin to make a hole in the cell – granzymes and granulysin induce apoptosis and DNA fragmentation

• This ↑↑ production of NO and superoxide radicals to optimise destruction of pathogens

• Fas ligand interactions induce apoptosis

• Activated APCs are able to activate specific CD8 T cells via MHC I and second signals:

• IFN-γ release blocks viral replication – Important not to actually lyse virally infected cells as this lets all the baby viruses out!

– B7 + CD28 – 4-IBBL + 4-IBB

T Cell Receptor Diversity

• In a second infection, only the first signal (MHC + antigen) is needed to activate the cytotoxic T cell response

– VDJ recombination by RAG proteins – junctional diversity (imprecise VDJ joining) – N regions (random addition of nucleotides) – NB// no class switching/hypermutation

• This means any APC is able to activate memory T cells  reduced need for CD4 T cell help  faster response

• Any T cells that react to self antigens are destroyed by the thymus

TCR

!*@!

MHC I

+++

TC CD8

IL-2

complement activation

TCR

inflammatory response (C3a, C4a, C5a)

MHC I

TC CD8 4-IBB

CD28

4-IBBL

infected cell

perforin, granzymes, granulysin induction of apoptosis

APC MBL

+++

MHC II TCR

TLR

dendritic cell

MHC II

CD40

IFN-γ CD40L

TH0 CD4

TCR MHC II

B7 CD28 CD40L

NK cell ↑↑ costimulatory molecules e.g. B7

CD40 IL-2 IL-4 IL-5

proinflammatory cytokine release IL-1 IL-6 IL-8 IL-12 TNFα

↑↑ CRP

• Viruses: usually intracellular z

fever

memory cell

plasma cell Y Y

neutrophil

neutralise toxins

Y antibodies IgM  IgG IgA IgE

microcoagulation to prevent spread of infection

humoral immunity T H2

chemotaxis increased capillary permeability  oedema and swelling

+++

B cell CD19

NF-ΚB activation

• Bacteria – extracellular  TH2  humoral immunity – intracellular  TH1  cell-mediated immunity with activated APCs and cytotoxic CD8 T cells

cell-mediated immunity T H1

TCR

PAMP PRR NO MHC I

Different types of infection

synapse formation (cells touch)

opsonisation of pathogens (C3b, C4b) MAC complex pathogen lysis (C5b-C9)

pathogen

• Same principle as B cell memory

• It is generated in the same way:

inflammation 4-96hrs

T Cell Memory

• T cell receptor diversity is just as vital as antibody diversity

CHO

CD8

• Activated CD8 T cells destroy infected cells

– CD40 ligand interactions – focal IFN-γ secretion

innate immunity 0-4hrs

CD8 T Cell Response

– TH1  cell-mediated immunity with activated APCs and CD8 T cells (plus antibodies) – IFNγ inhibits viral replication and spares cells – NK cells recognise and kill infected cells by binding to opsonising surface antibodies

opsonise pathogens activate complement activate effector cells

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Different types of infection • Fungi: usually extracellular – TH2  humoral immunity with ↑↑ macrophages

• Protozoa (response isn’t brilliant) – extracellular  TH2  humoral immunity – intracellular  TH1  ↑↑ APCs, CD8 T cells

• Worms: always extracellular – TH2  humoral immunity – eosinophils and IgE have a special role

Imperfect Immune Response • Failure of repertoire  immunodeficiency – lack of specific adaptive immune system

• Failure of rapidity  immunodeficiency – lack of innate immune system

• Failure of regulation  allergy, autoimmunity – failure of thymic “education” – inappropriate activation of immune response – lack of regulatory T cell function

Phagocyte Deficiencies • Neutrophils are extremely important – deficiency presents within days of birth

• Defects in phagocyte production  neutropenia and severe infections • Defects in adhesion molecules/chemotaxis  repeated infections, poor wound healing

• Defects in killing mechanisms  chronic granulomatous disease (CGD)

Perfect Immune Response • Has a diverse repertoire – generation of antibodies and T cell receptors

• Is rapid in its response to infection – innate immune system provides initial cover – memory cells allow rapid next response

• Is appropriately regulated – T cell “education” in the thymus – MHC restriction and second signals – regulatory T cells (Treg) and cell death pathways

Immunodeficiency • Primary: inherited/congenital • Easy to classify using immune response: – Phagocytes (18%) – Complement (2%) – B cells & antibodies (50%) – T cells (30%)

• Secondary: acquired (much more common)

Complement Deficiencies • C1/C2/C4 deficiency  abnormal immune complex formation  immune complex disease e.g. SLE

• C3 deficiency  defective opsonisation and chemotaxis  severe pyogenic infections e.g. Streps, HiB

• C5/C6/C7/C8/C9 deficiency  increased susceptibility to Neisseria

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Antibody Deficiencies

• ↑↑ susceptibility to extracellular pathogens

• X-linked agammaglobulinaemia (XLA)

• Bacteria: encapsulated pyogenic

• Common variable immunodeficiency (CVID)

– S. pyogenes, S. aureus, S, pneumoniae, HiB

• Viruses – Enteroviruses, echoviruses, hepatitis – Usually present as meningoencephalitis

• Protozoa – Giardia lamblia

T Cell Deficiencies • ↑↑ susceptibility to intracellular infections too • Bacteria: intracellular – mycobacteria, Salmonella

• Fungi – Candida, Aspergillus, Cryptococcus neoformans

• Protozoa – Pneumocystis, Toxoplasma, Cryptosporidium

• Viral infections (many)

• Transient hypogammaglobulinaemia of infancy • Selective IgA deficiency • Hyper-IgM syndrome (CD40L deficiency) • Thymoma

T Cell Deficiencies • NB// usually combined immunodeficiency due to loss of CD4 T cells • Wiskott-Aldrich syndrome (WAS) • DiGeorge syndrome/Nezelof syndrome • Ataxia telangiectasia (AT) • Severe combined immunodeficiency (SCID) – loss of EVERYTHING  – fatal by 1 year of age  treat with BMT

Acquired Immunodeficiencies • Infections – bacterial: acute, chronic e.g. TB – viral: HIV, measles, viral RTI  pneumonia

• Malignancy (especially haematological) – cancer itself and treatments used

• Immunosuppression

• Extremes of age (prematurity/elderly) • Malnutrition

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Hypersensitivity • “An exaggerated immune response to what the body perceives to be a potentially harmful foreign substance”, for example: – allergens  allergic reaction – self antigens  autoimmune disease – transplant grafts  rejection

• Essentially a failure of regulation • Hypersensitivity reactions are divided into 4 types by the Gell & Coombs classification

Type I Hypersensitivity • First exposure: internalisation – allergen binds to FcεRII (CD23) and IgE – this activates APCs and increases IgE levels – extra IgE binds to FcεRI on mast cells – mast cells are now sensitised to the antigen

• Second exposure: allergic reaction – allergen cross-links mast cell receptors – this stimulates degranulation and release of inflammatory mediators e.g. histamine

Anaphylaxis • Severe, systemic type I allergic reaction • Many possible precipitating allergens • Massive histamine release leads to: – vasodilation  urticaria, hypotension, shock – smooth muscle contraction  bronchoconstriction – chemotaxis  cellular infiltrate & tissue damage

• NB// anaphylactoid reactions are clinically similar but not IgE-mediated and therefore not as severe (preformed histamine only)

Type I Hypersensitivity • Affects 20-30% of the population • IgE antibody response to soluble antigen e.g. pollen, animal hair, house dust mites • Exposure to antigen activates mast cells, basophils and eosinophils  histamine release  immediate onset of allergic symptoms: asthma, rhinitis, eczema, anaphylaxis if severe

Atopy • Tendency to overproduce IgE • Presents clinically as: – allergic asthma – atopic rhinitis (hay fever) – atopic dermatitis (eczema) – allergic conjunctivitis – type I hypersensitivity e.g. food allergies

• May be a hereditary problem

Type II Hypersensitivity • Specific IgM or IgG antibodies bind to cell surface receptors or antigens  complement activation (classical pathway)  inflammation, phagocytosis and cell lysis

• Clinical examples: - rhesus disease - mismatched blood transfusions - autoimmune disease (reaction to self antigens)

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Type III Hypersensitivity

• Immune complex mediated (Ig + antigen)

• Disease depends on area(s) affected

• ICs activate classical complement pathway

• Clinical examples:

 release of anaphylotoxins C3a and C5a  inflammation, swelling, neutrophil chemotaxis

• ICs are deposited in vessels and tissues  blood vessel occlusion by platelets/thrombi  deposition in joints, glomeruli etc…  inflammation of tissues  damage  disease

TH CD4

Type IV Hypersensitivity

Skin  Arthus reaction Blood vessels  vasculitis Lungs  “farmer’s lung” Joints  rheumatoid arthritis Kidneys  glomerulonephritis Everywhere  systemic lupus erythematosus

TC CD8

• Cell mediated hypersensitivity reaction – takes 2-3 days

• T cell response is activated by APCs – CD4 cells activate specific humoral and cell mediated immunity – CD8 cells recognise antigens on cell surfaces and directly kill “infected” cells

• NB// can occur in combination with a type I response to the same antigen e.g. penicillin

Autoimmunity • The loss of immunological “tolerance” i.e. the ability of the immune system to differentiate self from non-self • In other words, the body mistakes self antigens for foreign pathogens and attacks them, resulting in disease • This is another form of immunodeficiency, as regulatory mechanisms have failed

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How does it happen?

• Failure of T cell selection in the thymus  production of self-reactive T cells

• “Confusion” of immune system (common) • Molecular mimicry by pathogens

– inherited syndromes e.g. AIRE mutations

– Strep A  rheumatic fever – Chlamydia  reactive arthritis – viruses e.g. HSV  myasthenia gravis

• Self-reactive T cells are activated in the context of infection and inflammation • Lack of T regulatory cells

• Exposure of normally hidden self antigens

- presence of infection downregulates function - immunodeficiency e.g. IPEX syndrome - immunosuppressive drugs

– pancreas  T1DM – immunoprivileged eye tissue

Autoantibodies: examples

Autoreactive T Cells: examples

• Type II hypersensitivity (cell surface Ag)

• Type I diabetes mellitus

– destructive e.g. Goodpasture’s syndrome (GBM) – receptor antagonism e.g. myasthenia gravis (ACh) – receptor agonism e.g. Grave’s disease (TSH) – haemolysis e.g. Rhesus disease of newborn (Rh)

– vs pancreatic islet beta cells

• Hashimoto’s thyroiditis – vs thyroid peroxidase (TPO)

• Rheumatoid arthritis

• Type III hypersensitivity (ICs)

– vs synovial membrane

– localised e.g. farmer’s lung – systemic e.g. SLE – post-infectious e.g. reactive arthritis, post-Strep glomerulonephritis

TCR

!*@!

innate immunity 0-4hrs

inflammation 4-96hrs

• Multiple sclerosis – vs myelin

MHC I

+++

TC CD8

IL-2

complement activation

TCR

inflammatory response (C3a, C4a, C5a)

MHC I

TC CD8 4-IBB

CD28 B7

4-IBBL

infected cell

perforin, granzymes, granulysin induction of apoptosis

– innate immunity: cells, chemicals, inflammation – antigen presentation to naïve T helper cells – antigen-specific adaptive immune response by antibodies and/or cytotoxic T cells

APC TCR

MHC II

dendritic cell

pathogen

+++

MHC II

TLR

IFN-γ CD40L

TCR

TH0 CD4

PAMP PRR NO MHC I

TCR MHC II

B7 CD28 CD40L

NK cell ↑↑ costimulatory molecules e.g. B7

CD40 IL-2 IL-4 IL-5

proinflammatory cytokine release IL-1 IL-6 IL-8 IL-12 TNFα

B cell CD19

↑↑ CRP

humoral immunity T H2

fever

memory cell

plasma cell

chemotaxis Y Y

neutrophil

• If any part of this response is inadequate or missing, the result is immunodeficiency • If it responds to harmless or self antigens, the result is allergy or autoimmunity • Control mechanisms are vital to prevent disease

neutralise toxins

Y antibodies IgM  IgG IgA IgE

increased capillary permeability  oedema and swelling

+++

NF-ΚB activation

microcoagulation to prevent spread of infection

cell-mediated immunity T H1

CD40

MBL

Summary • The normal immune response has 3 stages:

synapse formation (cells touch)

opsonisation of pathogens (C3b, C4b) MAC complex pathogen lysis (C5b-C9)

CHO

Psoriasis

opsonise pathogens activate complement activate effector cells

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Question 1

Question 2

Which of the following are second signal molecules?

a) Which is the most important APC?

dendritic cell

1) MHC II 2) CD40 ligand b) Which is the most important phagocyte?

3) IL-2

neutrophil

4) B7 5) 4-IBBL c)

6) NF-KB

Which is the most important T cell subtype?

TH CD4

7) sonic hedgehog protein

Question 3

Question 4

For each of the following statements, select true or false:

1) Type I hypersensitivity reactions are mediated by IgA antibodies 2) Type II hypersensitivity is triggered by antibodies binding to cell surface antigens 3) Type III hypersensitivity is triggered by antibodies binding to cell surface antigens 4) The Arthus reaction is an example of a type III hypersensitivity reaction 5) Type IV hypersensitivity reactions take a few hours to have an effect

Question 5

• What is this reaction and how should it be treated?

• Anaphylaxis • Treatment includes: – ABCs – oxygen, fluids etc… – adrenaline – steroids

good luck!

• What disease is shown? What is its aetiology?

http://gatesle.edu.ms/popa.php?k=anaphylactic-reactionpicture

Any Questions?

• Grave’s disease • Type II hypersensitivity • Autoantibodies which stimulate thyroid TSH receptors  hyperthyroidism