b cell development

Question 1

What does the bone marrow contain and provide for maturation of B
lymphocytes

Answer 1

a. Unique microenvironment for maturation (HSC)
b. Bone marrow stromal cells for support
c. Cell to cell integration and production of cytokines

d. Provide survival and differentiation signals via these cytokines ( & other
molectules)

Question 2

The maturation of B cells can be identified by changes in enzyme activity, CD
marker expression & synthesis of BCR. Some of these markers include:

Answer 2

a. CD34, CD10, CD127, CD19**, CD20 **
b. RAG 1 & RAG 2
c. TdT
d. Btk
e. Pre-B Cell Receptor
f. BCR (IgM first then IgD)

Question 3

CD127 Is?

Answer 3

IL-7 Receptor

Question 4

What stages of B-Cell development occur in bone marrow?

Answer 4

a. Development from Stem cell to Pro B Cell

Question 5

Stem cell H- chain/L – chain, Ig Status

Answer 5

Germline & No Ig

Question 6

What is the order of development of B cells?

Answer 6

Stem cell
early PRO-B cell  
Late PRO- B cell  
large PRE-B cell  
small PRE-B cell  
Immature B-cell

Question 7

Which chain (heavy or light) is re-arranged first

Answer 7

The heavy chain (H-chain) genes are rearranged before the light chain
genes

Question 8

At the early pro-B cell level in the bone marrow gene arrangement of the H-
Chain starts how?

Answer 8

Joining of the D and J genes on both chromosomes (maternal and paternal)

Question 9

If early pro-B cell level rearrangement productive what does the heavy chain
undergo at late pro-B cell stage?

Answer 9

a. V- DJ rearrangement takes place on the first chromosome (either paternal
or maternal).

b. If V- DJ rearrangement on the first chromosome not productive then
attempt on second chromosome

c. If  V- DJ rearrangement on the second chromosome not productive then 
apoptosis signaled (about 50%)

Question 10

What must accompany any productive heavy chain re-arrangement before
approval to become pre-B cell? (involving IgM)

Answer 10

The C(mu) gene is selected to complete the genes needed for IgM (VDJC(mu)) 
and further re-arranged with V-DJ

Question 11

If late pro-B cell level rearrangement productive what does the cell become?

Answer 11

Still late Pro- B cell

Question 12

What is the final step before a Pro-B cell can become a pre-B cell?

Answer 12

Functionality checking of µ chain

Question 13

How is this functionality checking done?

Answer 13

a. The late pro-B cell will express a surrogate light chain, to test if the heavy
chain can successfully pair with a potential light chain.

b. Expression of both the recombined heavy chain with the surrogate light
chain forms the pre-BCR, which is the first checkpoint in the
developing B cell.

c. If this pairing is appropriate, the pre-BCR will be expressed on the
surface of the cell

d. This expression will initiate signaling that indicates the cell is ready to
progress to the large pre-B-cell stage.

e. If the heavy chain is in some way defective or unable** to pair with the
surrogate light chain, the B cell will not receive the appropriate maturation
signals and will subsequently die by apoptosis**

Question 14

What is the significance of Bruton’s tyrosine Kinase (Btk) in this process?

Answer 14

a. Operates as apart of the signal to tell the cell that it has successfully
rearranged its Ig H chain and has made functional u chain to shut down
further H chain rearrangement, stop synthesis of surrogate chain, start L
chain gene rearrangement.

***b. Mutation in Bkt gene results in lack of differentiation to immature B cell level. Common in boys – X-linked agammaglobulinemia.

Question 15

What occurs at pre-B cell stage?

Answer 15

Light chain gene re-arrangement

Question 16

What becomes activated and starts gene re-arrangement of light chain in SMALL
pre-B cell?

Answer 16

RAG Enzyme

Question 17

Where does L-Chain rearrangement start in PRE-B Cell?

Answer 17

a. Recombination begins at the kappa ()-chain loci;
b. If not productive on both chromosomes the cell will then attempt recombination at the lambda ()-chain loci.

c. If none of these four opportunities work productive then signal for
apoptosis

Question 18

If re-arrangement productive what happens?

Answer 18

Once productive it will pair with the previously made heavy chain and
be expressed on the cell surface as BCR complex & be called an Immature B- Cell.

Question 19

Immature B-cell express?

Answer 19

IgM

Question 20

What has to occur before B-cell can leave bone marrow?

Answer 20

Check for self reactivity (third checkpoint)

Question 21

Self reactivity/ Self tolerance involves?

Answer 21

a. Immature B cell exposed to self antigen in bone marrow

b. If it recognizes self antigens in the bone marrow – allowed to change the 
light chain (kappa or lamda) but not the u chain  

c. If not, leaves bone marrow and enter secondary lymphoid where expresses
both IgD & Ig M

Question 22

How do B-cell express both IgD & IgM with the same VDJ (heavy chain)?

Answer 22

Alternative mRNA splicing

Question 23

Maturation and survival of B-cells requires?

Answer 23

Access to lymphoid tissue. If a B cell meets an antigen it proliferate to form the germinal center and became plasma cells – move to the medulla-
produce Ig. Those that do not meet the antigen of their specificity they
move to the medulla enter efferent vessel.