Lecture 19

Question 1

What is the structure of the B cell receptor? (two chains and the sections in each of those)

Answer 1

Light chain- Variable, constant, and joining regions

Heavy chain- Variable, Constant, D, and Joining regions

Question 2

True or false: B cell receptors and the antibodies produced by the B cells recognise different antigens

Answer 2

False: they recognise the same antigen

Question 3

Describe the mechanism of B cell gene recombination

Answer 3

Each sequence (V, D, J) has an adjacent recombination signal sequence

RSS recognised by two proteins- RAG1 and RAG2. These proteins cut the DNA.

TdT fixes the breaks and forms a coding joint (D-J or V-DJ for heacy, V-J for light) and a signal joint (deletes all the other DNA)

Extra nucleotides called N regions can be inserted at these joints

Question 4

What does “all B cells are monospecific” mean?

Answer 4

B cells are monospecific- all the antibodies that any one B cell produces has identical antigen binding sites. This enables antibodies to cross link antigens into large aggregates, thereby promoting antigen elimination.

Question 5

What is the T cell receptor structure? (chains and regions of the chains)

Answer 5

2 chains- Alpha and beta

Alpha chain- variable, constant, and joining

Beta chain- variable, constant, joining, and D region

Question 6

What is the primary control of diversity for both T and B cells?

Answer 6

V(D)J recombination

Question 7

What happens to a naive T cell in the thymus if it doesnt recognise MHC?

Answer 7

Death by neglect

Question 8

What happens to a naive T cell in the thymus if it binds strongly to self antigen?

Answer 8

Gets killed off

Question 9

What happens to a naive T cell in the thymus if it recognises but doesn’t respond to self peptide and binds to MHC?

Answer 9

Survives

Question 10

What are the stages of positive selection in the thymus? At each stage what receptors do the T cells have?

Answer 10

T cell precursors enter the thymus with no CD4 or CD8- are double negatives

Then they develop both receptors (become double positive). If they recognise MHC they grow and divide. If they do not recognise MHC they die by neglect.

Question 11

What happens during negative selection in the thymus?

Answer 11

Theres a selection process where T cells are screened to see what type of T cells they will become.

• If they react to self peptide, they get killed off.
• If they bind to MHCII, they keep their CD4 receptor and get rid of their CD8.
• If they bind to MHC1 they keep their CD8 and get rid of their CD4.