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infection & immunity > T Cells And TCRs > Flashcards

T Cells And TCRs Flashcards

1
Q

Where does T cell development occur

A

Produced in bone marrow

HSC precursor —> thymus to mature (thymocytes)

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2
Q

What does T cell maturation involve

A

Rearrangement of TCRs

Positive and negative selection (central tolerance)

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3
Q

What is central tolerance

A

Positive and negative selection
Surviving: thymocytes that recognise MHC I/II —> MHC restriction (positive)
Apoptosis: thymocytes that bind to self-peptides/MHC I/II complexes (negative) —> self tolerance

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4
Q

Describe the processes involved in T cell maturation

A
  • T cells rearrange TCRs genes
  • Expression of TCR (alpha-beta or gamma-delta chains)
  • Expression of both CD4 and CD8 co-receptors
  • Double positive (selection)thymocytes
  • generation of single positive thymocytes expressing TCR
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5
Q

What is a Double negative thymocytes

A

Expresses neither CD4 or CD8

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6
Q

What is a Double positive thymocyte

A

Express both CD4 and CD8

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7
Q

What is a single positive thymocyte

A

Expresses one of either CD4 or CD8

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8
Q

What is cluster differentiation (CD(4))

A

Membrane glycoproteins

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9
Q

Which type of CD molecules do MHC II cells bind to

A

CD4

Rule of 8, (MHC) 2 x (CD)4 = 8

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10
Q

Which type of CD molecules do MHC I cells bind to

A

CD8

Rule of 8, MHC (1) x CD(8) = 8

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11
Q

What are TCRs

A
  • Membrane bound glycoproteins similar to Fab fragment
  • 2 polypeptide chains: alpha-beta or gamma-delta
  • 3 regions: variable V, Constant C and membrane anchoring
  • Recognises only protein antigens presented on host cells by MHC I
  • T cells DO NOT produce soluble or antigen like molecules
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12
Q

Describe the TCR-alpha locus

A

Chromosome 14
70-80 V-alpha genes
61 J-alpha gene segments
1 C gene

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13
Q

Describe the TCR beta locus

A

Chromosome 7
52 V-beta genes
2x (1D gene, 7J genes, 1C gene)

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14
Q

Explain TCR diversity

A 
VDJ recombination
- TCRalpha locus: VJ recombination
- TCRbeta locus: VDJ recombination of alpha and beta chains
Junctional Diversity
NO somatic hypermutation
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15
Q

Functions of TCR

A

Naive TCRs and APC —> signalling cascade —> enhanced T cell cervical —> proliferation —> differentiate into distinct effector and memory Tc and Th subtypes

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16
Q

What is the maturation site for B cells

A

Bone marrow

17
Q

Maturation sure for T cells

A

Thymus (thymocytes)

18
Q

Difference between antibody and T cell specificity

A

Antibodies can recognise a variety of organic and inorganic molecules, T cells can only recognise protein antigens

19
Q

True or false: T cells secrete antibodies

A

False, B cells do

20
Q

True or false: T cells can recognise pathogens “By themselves”

A

False, B cells can, T cells have to have pathogen “presented” (opsonised) to them

21
Q

What are some similarities between T and B cells

A
  • Appearance, they look exactly the same
  • Origin, produced in bone marrow
  • TCRs are antibody-like molecules
  • Antibodies, BCRs and TCRs are generated by gene recombination
  • TCRs are diverse like BCRs and antibodies
  • T and B cells undergo clonal expansion after activation
  • Antibodies, BCRs and TCRs recognise regions of antigens called epitomes
22
Q

True or false: the adaptive immune response is launched when the innate response is overwhelmed

A

True

23
Q

What are the functions of a cell mediated response

A
  • Cell mediated cytotoxicity through Tc cells
  • Activation of cell phagocytes by Th
  • Activation of Tc and B cells by Th
  • Th - required for development of B and Tc memory cells
24
Q

What are the functions of CD8 T cells

A

Recognise antigens on MHC 1 APCs to activate cytotoxic effector functions
Destroy pathogen infected host cells

25
Q

What is the function of CD4 T cells

A

Recognise antigens on MHC 2 in APC

Th1: can secrete IL2, TNF-beta, IFN-gamma, cytokines to push class switch

Th2: IL4, IL5, IL6 and IL10 (cytokines) - push B cell class switch

26
Q

Characteristics of T regulatory cells

A

Express CD4/CD25 molecules

- recognise antigens on MHC 2 —> immunosuppressive: dominant negative regulation on other lymphocytes

27
Q

Where do B and T cells circulate

A

Naive B and T cells patrol the secondary lymphoid organs binding to matching antigens by APC —> Activation

28
Q

True or false: Professional APCs express antigens in their surface using both MHC I and II molecules

A

True

29
Q

True or false: uptake by endocytosis of pathogen leads to simultaneous cross-presentation if viral antigens on MHC 1 and 2 —> activating Th (CD4+) and Tc (CD8+)

A

True

30
Q

True or false: dendritic cells can cross-present

A

True

31
Q

Describe the mechanism for T cell activation

A
  • Interaction between antigen MHC complex and TCR supported by CD coreceptors
  • Interaction between T cell and APC
  • APC produce cytokines
32
Q

True or false: activation if T cells leads to the expression of IL4

A

False: IL2 turning into an effector or memory cell

33
Q

What is the role of activated CD4 (Th1) cells

A

Activate Tc cells
Activate B cells to produce openings —> Activation classical complement
Secrete IL2, IFN-gamma, TNF-alpha

34
Q

Role of activated CD4 (Th2) cells

A 
Secrete IL4, IL5, IL6 and IL10
Responsible for allergic reactions
Help control infection of parasites by:
- activating eosinophils and mast cells
- switching B cells to produce IgE antibodies
35
Q

What’s are the 2 processes of CD8 activation

A

Activation by nature dendritic cells (MHC1 —> IL2 —> Activation)
Activation with help of CD4 cells: CD4 IL2 —> increase in B7 —> CD8 Activation

36
Q

What is the role of activated (effector) CD8 (Tc) cells

A

Kill target cells infected with pathogens particularly viruses

37
Q

Describe the characteristics of the cytotoxic activity of NK and Tc

A

Fas-independant (perforin/granzymes)
Fas-dependant cytotoxicity
Fas-receptors in surface of target cel
Fas-ligand in surface of NK and Tc cells —> apoptosis

38
Q

What are the 4 stages of Fas-independent NK and Tc cytotoxicity

A
  • recognition and attachment to target cell
  • membrane attack: release of perforin/granzymes
  • NK/Tc dissociation
  • Target cell apoptosis

infection & immunity (17 decks)

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