B Cell Development

Question 1

What is required for the generation of antibodies?

Answer 1

Ig gene rearrangements

Question 2

What antibodies are made in the B Cells?

Answer 2

IgM

Question 3

What is the gene rearrangement process for the light chain?

Answer 3

The germ line DNA has the V gene rearrange with the J gene into a VJ gene. Then the genes between them are deleted. This forms the LVJ necessary for the expression of the light chain.

Question 4

What is the gene rearrangement process for the heavy chain?

Answer 4

The germ line DNA has the D and J rearrangement as the first to occur. Then a V and DJ rearrangement occurs and leads to the VDJ formation which is necessary for the heavy chain.

Question 5

Is Ab synthesis antigen driven?

Answer 5

No. The process occurs entirely independently and does so at random.

Question 6

For the heavy chain rearrangement, are there residual V genes?

Answer 6

Yes, upstream

Question 7

For the heavy chain rearrangement, are there residual D genes?

Answer 7

No, both upstream and downstream D genes will all be deleted

Question 8

For the heavy chain rearrangement, are there residual J genes?

Answer 8

Yes, downstream

Question 9

What are the steps in B cell development?

Answer 9

ProB -> PreB -> Immature B -> Mature B cells

Question 10

What is allelic exclusion?

Answer 10

Only one Vh and Vl is rearranged per B cell

Question 11

What process is occurring during the Pro B cell stage?

Answer 11

D-J and V-DJ rearrangement of the heavy chain

Question 12

What occurs on the surface in the Pre B cell stage?

Answer 12

Heavy chain binds to a surrogate light chain (as the true light chain rearrangement has not yet occurred) which takes it to the surface and gets a signal to turn off heavy chain rearrangement

Question 13

What else is occurring intracellularly in the Pre B cell stage?

Answer 13

V-J rearrangement of the light chain

Question 14

What occurs in an immature B cell?

Answer 14

VJ rearrangement of the light chain is complete and so complete IgM can be expressed on the cell surface

Question 15

What occurs in mature B cells?

Answer 15

They have gained antigen specificity and as a result, they can express IgM and IgD on the cell surface via alternative splicing

Question 16

What heavy chain is made by B cells?

Answer 16

Mu heavy chain

Question 17

What mediates the V, D and J recombination?

Answer 17

The RSS (recombination signal sequence) are highly conserved stretches of seven or nine nucleotides separated by non-conserved 12 or 23 nucleotide spacers.

Question 18

What recognizes the RSS and cleaves it?

Answer 18

RAG1 and RAG2

Question 19

What are BRECs and why are they important?

Answer 19

B cell Recombination Excision Circles. They are important because they can be used in marrow transplant patients in order to determine whether or not transplants have been accepted.

Question 20

How are secreted and membrane IgM generated with the same VDJ region?

Answer 20

Alternative mRNA splicing

Question 21

How are IgM and IgD generated from the same B cell?

Answer 21

Alternative mRNA splicing

Question 22

Where does the difference in the secreted and membrane IgM lie?

Answer 22

Difference in secreted and membrane antibodies lies in the C region of the gene

Question 23

What mediates the V/D/J rearrangements?

Answer 23

RSS and the RAG1 and RAG2 enzymes

Question 24

What mediates the isotope switch rearrangements?

Answer 24

Mediated by switch regions and

AID (activation induced cytidine deaminase)

Question 25

What are the factors that contribute to the diversity of the antibodies?

Answer 25

1. Combinatorial V(D)J gene joining 2. Combination of the Vh and Vl chains 3. N nucleotide addition by TdT 4. Somatic hypermutation

Question 26

What is somatic hypermutation?

Answer 26

It occurs after the cells leave the bone marrow and the cells divide, there is a massive increase in the rate of mutation in order to adapt to any possible antigen.

Question 27

What is N nucleotide addition?

Answer 27

TdT enzyme steps in after excision and randomly adds nucleotides to broken V and J ends after the BREC leaves and before they are ligated. The number and what is added is entirely random and this allows for the generation of entirely new DNA as a result.

Question 28

What enzyme is responsible to N nucleotide addition?

Answer 28

Terminal deoxynucleotidyl Transferase (TdT)

Question 29

What happens when the V(D)J rearrangements are non-functional?

Answer 29

The cells will die

Question 30

What is the most extreme outcome if an Ab is found to be self reactive?

Answer 30

They will get an apoptotic signal in the bone marrow and be destroyed

Question 31

Besides apoptosis, what else may happen to self reactive antibodies?

Answer 31

Self reactive Ab that reach the periphery will become anergic and they do not react to antigens which are self

Question 32

What is a process that can fix self reactive antibodies?

Answer 32

Receptor editing

Question 33

How does receptor editing work?

Answer 33

Anti-self B cells can undergo receptor editing which occurs with the up regulation of the protein RAG, leading to more rearrangements and the generation of a new B cell. If the new B cell is no longer self reactive, it can migrate to the periphery and become a mature B cell.

Question 34

Can receptor editing occur in the light chain?

Answer 34

Yes, there are V genes upstream and J genes downstream available for further rearrangement

Question 35

Can receptor editing occur in the heavy chain?

Answer 35

No. There are no further D genes available for rearrangement.

Question 36

What is the TCR and what is it similar to?

Answer 36

T cell receptor. It is similar to the Fab of the Ab on the B cells

Question 37

Where are T cells made?

Answer 37

In the thymus

Question 38

What rearrangement occurs on the alpha chain of TCR?

Answer 38

VJ

Question 39

What rearrangement occurs on the beta chain of the TCR?

Answer 39

VDJ

Question 40

What is the mediator of the TCR rearrangement?

Answer 40

RSS and RAG is the enzyme

Question 41

What are the excised loops of DNA from TCR rearrangement called?

Answer 41

T cell Rearrangement Excision Circles (TRECs)

Question 42

Do T cells undergo somatic hypermutation?

Answer 42

No

Question 43

How are the G, E and A Ab generated?

Answer 43

Isotype class switch rearrangement

Question 44

What is the switch region?

Answer 44

Where DNA switching occurs

Question 45

Where does the isotope class switch mutation occur?

Answer 45

Outside of the bone marrow