3. T cells

Question 1

What are the 3 checkpoints that need to be passed in T cell maturation?

Answer 1

TCR
Positive selection/ recognise MHC
Negative selection/ weakly recognise self antigen

Question 2

Describe the structure of the T cell receptor

Answer 2

Membrane bound protein with an a and B chain
Each has a variable and constant region
Each TCR is unique due to gene rearrangement

Question 3

What segments make up the V part of the TCR?

Answer 3

V
D
J

Question 4

What chromosome is the a chain of the TCR expressed?

Answer 4

14

Question 5

What chromosome is the B chain of the TCR expressed?

Answer 5

7

Question 6

Describe the process of positive selection

Answer 6

Epithelial and dendritic cells in the thymus express high MHC
Immature T cells bind and get positive signal to survive

Question 7

How is the type of T cell determined?

Answer 7

Whether it bound to MHC-I or -II in the thymus

Question 8

Describe the process of negative selection/central tolerance

Answer 8

MHC in the thymus only expresses self peptide

If the TCR binds too tightly to self-peptide then the T-cell commits apoptosis

Question 9

Where do immature T cells circulate?

Answer 9

secondary lymph organs

Question 10

How does a naive T cell become an effector T cell?

Answer 10

Activated once it recognises an antigen bound to MHC on DC
That T cell undergoes clonal expansion
Now an effector T cell

Question 11

What are the 3 signals needed to activate a T cell?

Answer 11

Antigen specific signal
Costimulation
Instructive cytokines

Question 12

How does the antigen specific signal work?

Answer 12

TCR recognises peptide of MHC-II

CD4 co-receptor reacts with residues on the side of MHC-II

Question 13

What does the activation of the TCR complex due to the antigen specific signal cause?

Answer 13

T cell starts to produce cytokines
Adhesion molecules on T cells bind to ligands on APC to stabilise the connection
T cell is primed but needs signal 2 to be activated

Question 14

What is costiumulation needed for?

Answer 14

Proliferation and differentiation of naive T cells

Question 15

Describe costimulation

Answer 15

Microbes stimulate APCs to express B7 which binds to CD28 (T cell surface receptor)

Question 16

What receptors inhibit activation of CD28?

Answer 16

CTLA-4

PD-1

Question 17

Which cytokine does the APC produce to ‘instruct’ T cells to become effect T cells?

Answer 17

IL-12

Question 18

How is clonal expansion initiated?

Answer 18

Activated T cells produce IL-2
The same cell increases IL-2 receptors
Autocrine signalling allows proliferation

Question 19

What defines the subset of T helper cells?

Answer 19

What cytokine it produces

Question 20

What are the functions of T helper cells?

Answer 20

Instruct macrophages to enhance killing

Instruct B cells to enhance antibody production

Question 21

Which cell does Th1 work with?

Answer 21

Macrophages

Question 22

Which cell does Th2 work with?

Answer 22

Eosinophils

Question 23

Which cell does Th17 work with?

Answer 23

Neutrophils

Question 24

How is homeostasis achieved after T cell activation?

Answer 24

Most will undergo apoptosis after the antigen is cleared
Deprived of activation signals (Cd28 and IL-2)
Activation of inhibitory pathways
T reg cells can dampen response

Question 25

Why is there poor T cell production in Di George syndrome?

Answer 25

Absent or hypoplastic thymus due to deletion on chromosome 22

Question 26

What are SCIDs?

Answer 26

Severe Combined Immunodeficiency

Mutations in genes that affect T and B cells

Question 27

What is the most common SCID in the world?

Answer 27

X-linked severe SCID
Mutation in IL-2R
Reduction in T cells, NK cells,
Non-functioning B cells

Question 28

What is the most common SCID in Ireland

Answer 28

Adenosine Deaminase Deficiency

dATP accumulates which inhibits cell division so that T and B cells can’t clone