Clonal Selection Theory and T Cell Development

Question 1

What 2 polypeptide chains is the TCR made of?

Answer 1

Alpha and beta chains

Question 2

The TCR is monovalent. What does this mean?

Answer 2

Single antigen binding site, can only bind one epitope at a time

Question 3

This is a non-polymorphic signalling complex found on all T-cells that mediates activation

Answer 3

CD3

Question 4

What are the 4 key events for T cell development in the thymus?

Answer 4

Gene rearrangement
TCR expression
Positive selection of TCR appropriate to host MHC
Negative selection of self-reactive TCR

Question 5

The T cell progenitor leave this tissue to travel to the thymus

Answer 5

Bone marrow

Question 6

This MHC class is found on all nucleated host cells

Answer 6

MHC I

Question 7

This MHC class is mainly on specialized APCs and can be induced on other cell by pro-inflammatory cytokines

Answer 7

MHC II

Question 8

What is the purpose of positive T cell selection?

Answer 8

To keep cells that are capable of recognizing self-MHC molecules
- if TCR can’t bind to MHC, it gets popped

Question 9

What is the purposed of negative T cell selection?

Answer 9

To get rid of T cells that are self reactive
makes sure cells are self-tolerant
too much affinity for self MHC = self-reactive

Question 10

What causes activation of a T cell?

Answer 10

Binding to an antigen-MHC complex that it has enough affinity for

Question 11

What are the 2 things that happen with T-cell activation?

Answer 11

Proliferation
Differentiation

Question 12

What determines which type of T-cell will be made with differentiation?

Answer 12

The type of MHC receptor the progenitor T-cell interacted with
MHC I = CD8 (cytotoxic)
MHC II = CD4 (helper)

Question 13

What do CD8 cells do?

Answer 13

Aka cytotoxic cells
Kill infected host cells
Some cytokine release

Question 14

What do CD4 cells do? (5)

Answer 14

Aka helper cells
Recruit cells
Activate phagocytic cells
Help B cells
Activate antigen presentation
T cell proliferation

Question 15

What is MHC restriction?

Answer 15

Requirement that TCR can only recognize and respond to antigenic peptide when it’s bound to an MHC molecule
CD4 can only recognize MHC II
CD8 can only recognize MHC I

Question 16

What is the role of MHC molecules?

Answer 16

Present self or non-self peptides to T cells

Question 17

What does the TCR recognize when interacting with an MHC molecule?

Answer 17

Peptide being presented by MHC
MHC polymorphic residue (recognizing the correct MHC allele)

Question 18

What is allele specificity in context of MHC and TCR?

Answer 18

Ppl have different MHC alleles —> presentation of different peptides
TCR has to recognize different alleles to ID the MHC-antigen complex correctly to mount an immune response

Question 19

If an auto reactive B cell doesn’t undergo negative selection, what happens?

Answer 19

Denied help from CD4 T cells —> no isotype switching or somatic hypermutation
If this fails, need drugs to fix autoimmunity

Question 20

If T cells that are autoreactive make it past negative selection, what happens?

Answer 20

Engaging self-antigens on cells that aren’t APCs means a lack of activation since the cell doesn’t have the key to activate it
Naive T cell is inactivated