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MCD > Immunology 7 - Effector T lymphocytes > Flashcards

Immunology 7 - Effector T lymphocytes Flashcards

1
Q

What is a naive T cell?

A

A mature recirculating T cell that has not yet encountered antigen.

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2
Q

What are effector T cells?

A

T cells that have encountered antigen, proliferated and differentiated into cells that participate in the host defense.

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3
Q

What are memory T cells?

A

T cells that have encountered antigen, contracted, ready to respond to future infections.

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4
Q

What are target cells?

A

Cells on which effector T cells act.

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5
Q

Why is a cell mediated response needed when we have an antibody response? Give 2 reasons.

A
  • Intracellular pathogens such as TB and malaria hide in the cell.
  • Some organisms are evolved to escape recognition by antibodies (either by changing shape (influenza), by coating the 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
  • Improves digestion by activating macrophages and causing inflammation (cytokine secretion)
  • By killing infected cells
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7
Q

How do antigen presenting cells induce the T lymphocyte response?

A
  • Dendritic cells are the main type of APC
  • They acquire antigens in tissues via surveillance
  • They then move to the lymph nodes (activated by PAMP)
  • In lymph nodes, they mature and then present antigen on MHC
  • T cells detect antigen via TCR and mature to effector T cells
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8
Q

What genes encode for MHC in humans?

A

HLA genes

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9
Q

Where do T cells enter they lymph nodes in recirculation?

A

High-endothelial venules (specialised areas in post-capillary venules)

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10
Q

List the three phases of cell mediated immunity

A
  • Induction
  • Effector
  • Memory
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11
Q

What occurs in the induction phase of cell mediated immunity?

A

The cell is infected, and DC detects this and forms an MHC

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12
Q

What occurs in the effector phase of cell mediated immunity?

A
  • The MHC peptide and TCR interact, causing the naive T cell to become an effector.
  • Effector cells see MHC-Peptide on the infected cell and performs its function.
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13
Q

What occurs in the memory phase of cell mediated immunity?

A

The effector pool contracts to memory, with many cells dying (apoptosis)

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14
Q

Describe the 3 signal model

A

The three signals required to stimulate a naive T cell are:

  • Antigen recognition
  • Co-stimulation
  • Cytokine release
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15
Q

Describe the role of cytotoxic T cells.

A
  • Cytotoxic T cells destroy target cells such as virus infected cells or tumours
  • Recognise MHCI: Peptide Complexes
  • CD8 T cells
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16
Q

How do cytotoxic T cells induce apoptosis?

A
  • They cause polarization within the cell of cytoxic vesicles
  • Release granules
17
Q

How is apoptosis characterised?

A

Fragmentation of nuclear DNA

18
Q

What do cytotoxic T cells store in granules?

A

Perforin, granzymes and granulysin

19
Q

What does perforin do?

A

Polymerise to form pores

20
Q

What does FasL do and where is it present?

A
  • Present on CD8

- Induces cell death by interacting with Fas on target cells

21
Q

List the T helper cell subsets

A
  • T helper 1 cells (Th1)
  • T helper 2 cells (Th2)
  • Follicular helper T cells (Tfh)
  • Th17 cells
  • Treg
22
Q

What is the role of Th1 cells?

A
  • Produce Interferon gamma
  • Activate macrophages to increase receptors displayed
  • Responsible for delayed type 4 hypersensitivity
23
Q

What is the role of Th2 cells?

A
  • Produce IL4, IL-5, IL-13

- Boost anti-multicellular organism response

24
Q

What is the role of Tfh cells?

A
  • Produce IL-21, reside in B cell follicles

- Essential for generation of isotype-switched antibodies

25
Q

What is the role of Th17 cells?

A
  • Secrete IL-17 in autoimmune diseases such as arthritis
  • Important for control of bacteria
  • Note other Th cells defined by cytokines e.g. Th9 (IL-9) and Th22 (IL-22)
26
Q

What is the role of Treg cells?

A
  • T cells that regulate the activation or effector functions of other T cells
  • Natural and induced regulatory T cells
  • Necessary to maintain tolerance to self antigens
27
Q

How are T helper cells defined?

A

By the cytokines they produce and the transcription factors they use

28
Q

What is delayed type hypersensitivity?

A
  • An effector function of T cells
  • It is the eradication of intracellular pathogens
  • If the antigen is not eradicated there is chronic stimulation
29
Q

How is delayed type hyersensitivity involved in allergy?

A

The T cell binds to the antigen, and is activated. The T cell then activates eosinophils to cause inflammation.

30
Q

What types of T lymphocytes are involved in delayed type hypersensitivity and what is their role?

A
  • Th2 activates eosinophils

- Th1 activates macrophages

31
Q

What are the two stages of the delayed type hypersensitivity response?

A
  • Dendritic cell takes up antigen and this causes an immune response resulting in immunological memory forming (sensitisation)
  • Effector phase is where the activated T cells cause the allergic response.
32
Q

what is the difference between memory T cells and naive T cells?

A

Memory T cells:

  • Have less stringent activation
  • Proliferate faster
  • Express different chemokine receptors
33
Q

Do T cells undergo isotype switching or affinity maturation?

A

No - only B cells undergo these processes

34
Q

What processes do T cells undergo for the second expansion to occur?

A

1) Naive T cells are activated
2) Primary expansion occurs
3) Contraction to form memory cells
4) Memory cells activated
5) Secondary expansion

35
Q

What is T cell exhaustion?

A
  • Over time, CD8 pool contracts to prevent excess damage, which increases risk of inflammation when the infection is not fully cleared.
  • Used in immunotherapy
36
Q

What are the pathological reactions of T cells?

A
  • Autoimmunity (antigenic peptide derived from self protein)
  • Regection of transplants (antigenic peptide from self protein of donor)
37
Q

List the 4 effector functions of T cells

A
  • Macrophage activation
  • Delayed Type Hypersensitivity
  • B cell activation
  • Regulation

MCD (56 decks)

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