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MIIM30002 - Principles of Immunology > Lecture 23 - Cell-mediated Effector Function > Flashcards

Lecture 23 - Cell-mediated Effector Function Flashcards

1
Q

In general, what is required for pathogen clearance?

A

An adaptive immune response

Ab and CTLs

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2
Q

What are the two arms of the adaptive immune system?

Describe the features of each

A
  1. Humoral
    • Ab
    • B cell mediated
    • Extracellular pathogens
  2. Cellular
    • CTLs
    • T cell mediated
    • Intracellular pathogens
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3
Q

What are the two subsets of conventional T cells?

A
  1. CTLs

2. “Helper” T cells

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4
Q

What are the principle effector mechanisms of activated T cells?

A
  1. Cytotoxins
    • Granzymes
    • Perforin
  2. Membrane associated effector molecules
    • FasL
    • CD40L
  3. Soluble cytokines
    • IFN-γ
    • IL-5
    • IL-17
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5
Q

What are the categories of effects of cytokines?

A
  1. Local
    • Cell-cell contact
    • Membrane cytokines
  2. Regional
    • Chemotactic effects
  3. Distal
    • Hematopoiesis
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6
Q

Compare T-cell effector functions for the following:
• Intracellular pathogens in cytosol
• Intracellular pathogens in phagocytic compartments
• Small extracellular pathogens
• Large extracellular pathogens

A

Intracellular pathogens in cytosol:
• CD8+ T cell mediated killing

Intracellular pathogens in phagocytic compartments:
• Th1 mediated IFN-γ responses

Small extracellular pathogens:
• Th17 mediated neutrophilic responses

Large extracellular pathogens:
• Th2 mediated IL-5 and IgE responses

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7
Q

What are IFN-γ responses good for?

A

Intracellular pathogens in phagocytic compartments

By triggering respiratory burst in macrophages

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8
Q

What response is best for small extracellular pathogens?

A

Th17 mediated neutrophilic responses

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9
Q

What response is best for large extracellular pathogens?

A

Th2 mediated IL-5 and IgE responses

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10
Q

Which response is best for intracellular pathogens?

A

In cytosol:
• CTL killing

In phagocytic compartments:
• IFN-γ

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11
Q

How do T cells get into the tissue?

Why would they need to do this?

A

After activation in the secondary lymphoid organs, they need to recirculate to the infected tissue to perform their effector function

Mechanism:
• Release of cytokines from infected tissue
• Expression of adhesion molecules on the T cells and endothelial cells

→ Rolling: selectins
→ Activation: chemokines
→ Adhesion: integrins
→ Diapedesis: chemokines

• Draining of T cells into efferent lymphatics → blood → tissue

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12
Q

Describe the molecule interaction during T cell rolling in migration to the skin

A

On vascular endothelium:
• E-selectin
• P-selectin

T-cell:
• CD43
• PSGL1

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13
Q

Describe the molecule interactions in the ‘activation’ step of T cell migration to the skin

A

T cell:
• CCR4
• CCR10

Keratinocytes:
Release of:
• CCL17
• CCL27

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14
Q

Describe the molecule interactions in the ‘Adhesion’ step of T cell migration to the skin

A

Endothelium:
• ICAM-1
• VCAM-1

T cell:
• LFA-1
• VLA-4

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15
Q

What brings about the expression of selectins and integrins on endothelium?

A
  • TNF-α
  • IFN-γ

Produced by innate cells in the infected tissue

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16
Q

Describe the molecule interactions in the ‘Rolling’ step of T cell migration to the gut

A

T cell:
• α4β7 integrin
• PSGL1

Endothelium:
• MAdCAM1
• P-selectin

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17
Q

Describe the molecule interactions in the ‘Activation’ step of T cell migration to the gut

A

T cell:
• CCR9

Chemokine release by enterocytes:
• CCL25

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18
Q

Describe the molecule interactions in the ‘Adhesion’ step of T cell migration to the gut

A

T cells: α4β7 integrin

Endothelium: MAdCAM1

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19
Q

Which chemokine is involved with T cell homing to the gut?

What is the receptor for this?

A

CCL25

Receptor: CCR9

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20
Q

What is the effect of the ‘activation’ step in T cell homing?

A

Conformational change in integrins → Adhesion

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21
Q

Describe tissue specific migration to the skin

A
  1. Vit D metabolites in skin
  2. DC experiences these metabolites and changes phenotype
  3. Travels to regional lymph node
  4. Skin imprinted DC interacts with naïve T cell and induces CCR10, CCR4, P- and E-selectin ligand (i.e. CD43 and PSGL) expression on the T cells
  5. T cells home to skin
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22
Q

Describe ‘imprinting’ and T cell homing to the gut

A
  1. Dietary vitamin A present in interstitial tissue in gut
  2. DC experience these metabolites and changes phenotype
  3. DC draining to LN
  4. ‘Gut’ imprinted DC interacts with naïve T cell and induces CCR9 and α4β7 expression
  5. T cells home to gut tissue
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23
Q

Compare lymphocyte infiltrate in the dermis of infected and non-infected mice

A

Non-infected:
• Low overall levels
• No CTLs
• A few helper T cells

Infected:
• High levels of T cell infiltrate

24
Q

What are Th1 good for?

A

Intracellular pathogen responses through production of IFN-γ

25
Q

Which cytokines lead to differentiation into Th1?

A

IL-12
IFN-γ

(released from DC)

26
Q

What is the effector function of IFN-γ?

A
  1. Macrophage activation
    → increased antigen presentation → increased CTL activation
  2. Killing of intracellular pathogens
    Through respiratory burst
  3. Expression of inflammatory mediators by infected cell
    → recruitment of T cells to site of infection
27
Q

What are Th2 good for?

A

Parasite infections

28
Q

How are Th2 induced?

A

IL-4 released from Mast cells, Eosinophils (?)

29
Q

Which cytokines do Th2 produce?

A

IL-4
IL-5
IL-13

30
Q

Describe the effector function of Th1

A

Effector functions:
1. Macrophage activation
• IFN-γ

  1. Killing
    • FasL
  2. Proliferation of T cells
    • IL-2
  3. Differentiation of other cell types in BM
    • GM-CSF
    • IL-3
  4. Endothelial activation
    • Lymphotoxin (LT)
    • TNF-a
  5. Chemotactic events
    (recruitment of more inflammatory cells)
    • CXCL2
31
Q

Describe the effector function of Th2

A
  1. B cell IgE production
    • IL-4
  2. Mast cell degranulation
    • Through IgE production
  3. Barriers: mucous production in GIT and peristalsis
    • IL-4
    • IL-13
  4. Eosinophil activation
    • IL-5
  5. Alternative macrophage activation
    • IL-4
    • IL-13
    → enhanced fibrosis / tissue repair
32
Q

Which cytokines stimulate the differentiation into Th17?

A

IL-6 & TGF-β

33
Q

Which transcription factors are important for Th17?

A

RORγT

34
Q

Which cytokines do Th17 produce?

A

IL-17
IL-22
IL-6

35
Q

What are the effector functions of Th17?

A
  1. Neutrophilic responses
    • IL-17
  2. Increased barrier function
    • IL-22
36
Q

Outline the effector function mechanism of CTLs

A
  1. Non-specific adhesion
    • Integrins etc
    • Does not activate the T cell
  2. Specific recognition
    • MHC I/peptide complex - TCR
    (peptide antigen from e.g. virus)
    • Brings about activation of the T cell
  3. Activation of T cell
    • Cytoskeletal changes in the T cell
    • Golgi apparatus polarised towards infected cell
3. Granule release
• Via exocytosis
• Perforin
• Granzymes
• Granulysin
• Release only towards infected cell
  1. Detachment
  2. Target cell death
37
Q

What are the cytotoxic substances released by CTLs?

What is the role of each?

A
  1. Perforin:
    • Form pores in membranes
    • Aids delivery of other cytotoxic mediators (granzymes)
  2. Granzymes
    • Proteases
    • Induces apoptosis through activation of pro-caspase 3 and BID

Both these need to be present for killing to occur

To a lesser degree:

  1. Granulysin
    •Antimicrobial found only in humans
  2. Serglycin
    • The scaffold for perforin and granzyme
38
Q

What is the structure of the complex released by CTLs?

A

Serglycin
• Forms a complex with perforin and granzymes
• Complex then released towards virally infected cell

39
Q

What is the function of granulysin?

A
  • Only in humans
  • Induces apoptosis
  • Also has antimicrobial actions
40
Q

Describe the mechanism of action of granzymes

A

Activation of:
1. BID

Activated BID:
• Interacts with Bax and Bak
→ Pore formation in mitochondria
→ Loss of cytochrome c into cytosol

  1. Pro-caspase 3
  • Activated pro-caspase 3 activates DNAases
  • Fragmentation DNA in the cell

Outcome: Target cell killed

41
Q

Where are Bax and Bak located?

A

On the outer membrane of mitochondria

42
Q

What are the features of the cell death induced by CTLs?

A

Immunologically quiet:
• No adjacent inflammation
• No release of pathogens

43
Q

Describe the Fas-FasL pathway

A
  • Alternative mechanism of T cell killing
  • Carried out by Th cells
Mechanism:
• Effector T cell expresses Fas L
• Target cell expresses Fas
1. Interaction of the ligands
2. Intracellular Death domains on Fas come together
3. Recruitment of FADD
4. Activation of caspase 8 by FADD
5. Apoptosis
44
Q

What is the role of the death domain?

A

Intracellular part of the Fas receptor

  1. Recruits caspase 8 when Fas is ligated
  2. Auto-activation of caspase 8
  3. Cell death through apoptosis
45
Q

What is happening in Autoimmune lymphoproliferative disease?

A
  • Mutation in Fas-FasL pathways
  • Dysfunctional apoptosis of lymphocytes
  • Enlarged LN, full of T cells that were not removed at the end of an immune response
46
Q

What is the first interaction between virally infected cells and CTLs?

A

Non-specific recognition

e.g. integrins

47
Q

Which Th subsets are important for barrier protection?

A
  • Th2

* Th17

48
Q

Describe, in general, effector T cell homing to specific tissues

A

“Imprinting”

Specific compound in the tissue drained by certain LNs
These compounds activate the lymphocytes in these LNs, and induce them to home back to these tissues

49
Q

Which component of CTL granules is only found in humans?

A

Granulysin

50
Q

Which Th subsets activate macrophages?

A

Th1: M1 inflammatory macrophages

Th2: M2 fibrotic macrophages

51
Q

When is Fas killing usually employed?

A

Apoptosis of effector T cells after the pathogen has been cleared

52
Q

Describe T cell help for macrophages

A
  1. Infected macrophage is expressing bacterial peptide in the context of MHC class II
  2. Th1 recognises the MHC II:peptide complex with its TCR
  3. Th1 releases IFN-γ onto macrophage which expresses the receptor
  4. CD40L on Th1 ligates CD40 on macrophage
  5. Macrophage is stimulated to undergo respiratory burst, and is better able to kill the pathogen in its endocytic compartments
53
Q

After activation in LNs, which molecules do T cells up-regulate, and which do they down-regulate?

A

Down-regulation:
• CD69
• CD62L
• CCR7

Up-regulation:
• CCR4/10 (skin)
• CCR9 (gut)
• α4β7 integrin (gut)
• PSGL-1
• CD43 (skin)
• LFA-1, VLA-1 (skin)
54
Q

What are CD62P and CD63E?

A

P- and E-selectin

Expressed on vascular endothelium in skin when infected

Recruitment of skin-tropic activated T cells (expressing PSGL1 and CD43 )

55
Q

What is the ligand for CD62E?

A

CD43

56
Q

What is the ligand for CD62P?

A

PSGL1

57
Q

What is the ligand for MAdCAM1?

A

α4β7 integrin

MIIM30002 - Principles of Immunology (30 decks)

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