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Immunology > 7. Effector T cells > Flashcards

7. Effector T cells Flashcards

1
Q

Naïve T cells

A

mature recirculating T cells that have not yet encountered antigen

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2
Q

Effector T cells

A

encountered antigen, proliferated and differentiated into cells that participate in host defence

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3
Q

Memory T cells

A

Encountered antigen, contracted, ready to respond to future infections.

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4
Q

Target cells

A

Cells on which effector T cells act

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5
Q

Why do we need cellular response?

A

Sometimes Antibody is insufficient (humoral immunity)
Some pathogens are intracellular: hidden in cell (TB, malaria, HIV etc)
Organisms evolve to escape antibody recognition: either by changing shape (influenza) or by coating antigen in carbohydrate (HIV) or producing decoy antigens (RSV)

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6
Q

How does Cell mediated immunity protect us against intracellular pathogens?

A

Enables digestion of pathogens/ infected cells: T cells instruct macrophages to digest
Enables better killing: CD4 instruct CD8 cells to respond and kill infected cells

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7
Q

Where are dendritic cells located?

A

In tissues:

surveillance: looking for broadly foreign non self-material

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8
Q

What happens when a DC acquires an antigen?

A

Move to lymph nodes (needs activation by PAMP/ PRR)
In lymph nodes, DC mature and then present antigen on MHC
T cells detect antigen via TCR and mature to effector T cells

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9
Q

Describe MHC I peptides

A

Intracellular

Bind to CD8

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10
Q

Describe MHC II peptides

A

Extracellular

Bind to CD4

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11
Q

Why and where do T cells recirculate?

A

Recirculation increases likelihood of encountering antigen
Recirculate from blood and lymph to lymphoid organs
Enter lymph nodes through specialised areas in post-capillary venules (high-endothelial venules)

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12
Q

Describe cell mediated immunity

A

DC acquires viral antigens and moves to lymph node
Specific T cells move out of circulation and into lymph looking for DC.
Finds specific DC.
T Cell sees MHC peptide complex, causes activation of T Cell (now effector)
Effector T Cell moves to site of infection- sees infected cells as have same MHC peptide complex on cell surface.
Clears infection
Effector pool contracts down to memory pool (most die)

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13
Q

What are the 3 signals required from DCs to activate a T cell?

A

Antigen Recognition: If T cell has not seen antigen for which it is specific for, it will not activate, so DC has to have MHC showing specific antigen
Co-stimulation: Surface-surface interactions, on DC surface, enabling clustering of receptors on T Cell surface
Cytokine Release: soluble interaction, DC release molecules which instruct T Cell to be activated

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14
Q

What are the 4 effector functions of CD4+ T Lymphocytes?

A

Macrophage Activation
B cell Activation
Delayed Type Hypersensitivity
Regulation

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15
Q

Which T lymphocyte subset is involved in cell mediated cytotoxicity?

A

CD8

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16
Q

Describe action of CD8+ cells

A

CD8 Cell scans MHC I checking for self
Virus infected cell has viral proteins- these get ‘chopped up’ and placed in MHC I complex as antigens- flags that it is infected
CD8 T cell recognises MHC I with viral proteins: this activates CD8 cell which kills infected cell

17
Q

How do CD8 cells induce apoptosis in their target cells?

A

CTL store perforin, granzymes and granulysin in cytotoxic granules
Granules are released after target recognition
Perforin molecules polymerise, form pores that CD8 can inject granzymes to drive apoptosis
Fas ligands on CD8 can induce apoptosis by interacting with Fas on target cell

18
Q

How many cells can CD8 cells kill?

A

Multiple (unlike neutrophils)

19
Q

How are T helper subsets defined?

A

By the cytokines they produce and transcription factors they use

20
Q

What are the 5 T helper cell subsets?

A 
Th1
Th2
Th17 
Follicular T helper cells 
Treg
21
Q

What is the role of Th1 cells?

A

Produce Interferon gamma (cytokine which informs immune system to be antiviral)
Boost intracellular immune response
Communicate with CD8

22
Q

What is the role of Th2 cells?

A

Produce IL4, IL-5, IL-13 (inform immune response to be anti-multicellular organism)
Boost anti-multicellular organism response
Communicate with Eosinophils

23
Q

What is the role of Follicular helper cells?

A

Produce IL-21, reside in B cell follicles
Essential for generation of isotype-switched antibodies
Communicate with B Cells

24
Q

What is the role of Th17 cells?

A

Secrete IL-17 in autoimmune diseases
Communicate with Neutrophils leading to killing of bacteria
Important for control of bacteria

25
Q

What is the role of Treg cells?

A

Regulate activation or effector functions of other T cells
Control response afterwards
Natural and induced regulatory T cells
Necessary to maintain tolerance to self-antigens

26
Q

Effector function 1 of T helper cells

A

Inflammatory Th1 effector cells activate macrophages to promote killing of intracellular pathogens

27
Q

Describe the 2nd effector function of T helper cells: Delayed Type Hypersensitivity

A

Primary role in defence and eradication of intracellular pathogens
If source of antigen is not eradicated causes chronic stimulation and granuloma formation
If antigen is not a microbe, like in contact hypersensitivity, DTH produces tissue injury without protection

28
Q

What are the 2 phases involved in Delayed Type Hypersensitivity?

A

Sensitisation: initial exposure to the antigen
Effector: delayed response

29
Q

Describe effector function 3 of t helper cells: B cell activation

A

2 events simultaneously happen
DC and B Cells both at site of infection and both take up same pathogen.
Both present antigen on MHC II complex
T Follicular Helper Cell specific to pathogen on DC recognises and becomes activated
Looks for B Cell with same antigen, instructs B Cell to perform effector function (Become Plasma or memory cell)

30
Q

How do memory T cells differ to memory B cells?

A

T cells don’t undergo isotope switching or affinity maturation

31
Q

How do memory T cells differ qualitatively to naive T cells?

A

Memory T cells have:
Less stringent activation (Less licensing)
Proliferate faster
Express different chemokine receptors

32
Q

Summarise the 4 stages T memory cells undergo

A

Expose
Expand
Contract
Memory

33
Q

Describe the life of T memory cells

A

Person becomes infected
T cells are exposed and proliferate (antigen specific T cells)
Infection is removed
Contraction of T cell pool, reserved as T cell memory

34
Q

Where and why are there subsets of T memory cells?

A

Different types of immune memory cells

Live in site of infection

35
Q

What causes T cell exhaustion?

A 
If source of antigen doesn't disappear T cells constantly proliferate 
Over time (esp. chronic infections) T cells become exhausted and senesce
36
Q

T cell exhaustion is very dangerous to the body, but what situations in particular?

A

Cancer/ HIV where infection is not fully cleared

37
Q

Beneficial actions of effector T cells

A

Recognition of antigenic peptides and clearance of pathogen

38
Q

Pathological reactions caused by effector T cells

A 
Autoimmunity (antigenic peptide derived from self-protein)
Transplant rejection (antigenic peptide derived from self-protein of donor)
39
Q

When can immune responses have negative outcomes?

A

When in excess of what is required
When in wrong anatomical compartment
When targeted against self (autoimmunity)
When targeted against benign antigens (allergy)

Immunology (9 decks)

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