Ab diversity/B cell development (class)

Question 1

T/F each Ig molecule produced by any one B cell is identical

Answer 1

true

Question 2

What is the complete collection of antibody (BCR) specificities generated by somatic recombination?

Answer 2

antibody repertoire

Question 3

T/F each B cell displays many copies of the same BCR
on its surface

Answer 3

true

Question 4

incredible repertoire of B cell receptors is generated via a unique genetic mechanism known as what?

Answer 4

somatic recombination

Question 5

Describe the characteristics of somatic recombination

Answer 5

“totally” random process that is antigen-independent

mediated by two enzymes (RAG-1 and RAG-2; the
recombination activation genes)

Question 6

In the lambda light chain locus, which parts are constant? describe how they are arranged…VJC

Answer 6

(L) V –V–V ——J–C—-J—C—–J—–C

C regions are constant, V and J are variable

Question 7

In every B cell, which chain occurs first?

Answer 7

heavy chain always occurs first

Question 8

Every B cell Ab is identical for what reason?

Answer 8

allelic exclusion

only 1 chromsosome is used at a particular time

Question 9

pairing of V and J gene segments gives rise to many different what?

Answer 9

λ or κ light chain variable regions

Question 10

pairing of V, D, and J gene segments gives rise to many different what?

Answer 10

heavy chain variable regions

Question 11

Joining segments provide some diversity. But what gives the light more diversity to the coding region?

Answer 11

recombination of light chain when the joining of gene segments occurs because it is not precise

this gives it more generated

Question 12

Why is Somatic Recombination of Ig Genes Such an Important Mechanism?

Answer 12

• the human genome contains approximately 40,000 genes
• the immunoglobulin genes code for up to 10^11 different antibody molecules (B cell receptors)

Question 13

Give a general description of class switching

Answer 13

Change-Out of Constant Domains of the Heavy Chain

Question 14

What is mutation that occurs at high frequency in the rearranged variable-region DNA of Ig genes in activated B cells, resulting in the production of variant antibodies, some of which have higher affinity for the antigen?

Answer 14

somatic hypermutation(affinity maturation)

Question 15

Where does affinity maturation occur? and how it coincides with B cells?

Answer 15

• occurs in follicles in secondary lymphoid tissues
• B cells that express higher affinity Abs are positively selected

Question 16

Cassette system of gene segments recombination occurs via what? describe it

Answer 16

somatic recombination

• antigen independent
• imprecise joining of gene segments
• pairing of rearranged light and heavy chains

Question 17

What is ability of B cells to change the isotype of the Ab it produces (without changing the antigen specificity)? describe it

Answer 17

class switching

• antigen dependent
• this enables the immune system to select the type of Ab that is needed to best deal with the invading pathogen

Question 18

Affinity maturation is synonymous with what?

Answer 18

somatic hypermutation

Question 19

Is somatic hypermutation(affinity maturation) antigen dependent or independent?

Answer 19

antigen dependent

Question 20

What enzyme is involved in signal transduction from cell-surface receptors during B cell development? What is this used for?

Answer 20

Bruton’s thymidine kinase (Btk)

B cell development

Question 21

What genes make double- stranded breaks in DNA during somatic recombination? What is the reason for these?

Answer 21

recombination activation genes (RAG-1 and RAG-2)

B cell development

Question 22

What enzyme catalyzes addition of N nucleotides at the junctions between rearranging gene segments? Why is this important

Answer 22

terminal deoxynucleotidyl transferase (TdT)

necessary for B cell development

Question 23

What enzyme catalyzes switch recombination (class switching); also required for somatic hypermutation (affinity maturation)? Why is this important?

Answer 23

Activation-induced cytidine deaminase (AID)

B cell development

Question 24

Describe the class switching WRT steps involved

Answer 24

1. isotype switching signal received
2. looping-out of DNA occurs
3. switch region recombination occurs (intervening DNA is removed)

Question 25

Without expression of IL-7, what will not occur? What is this molecule?

Answer 25

B cell repertoire

B cell growth factor

Question 26

BM stromal cells are critical for B cell development. Describe this path to an immature B cell

Answer 26

1. Lymphoid progenitor => CAMs, VLA-4, VCAM-1 (help bind to BM stromal cell)
2. early pro-B cell=> Kit, SCF (help bind to BM stromal cell)
3. late pro-B cell => once bound to BM stromal cell, IL-7 produced
4. pre-B cell => CAMs provide binding to BM stromal cell
5. immature B cell that is always 1st an IgM

Question 27

Give the 7 stages of B cell development

Answer 27

1. stem cell
2. early pro-B cell
3. late pro-B cell
4. large pre-B cell
5. small pre-B cell
6. immature B cell
7. mature B cell

Question 28

Describe the HC rearrangement of the 7 steps of B cell development

Answer 28

1. stem cell => germline
2. early pro-B cell => DJ rearranging
3. late pro-B cell => V-DJ rearranging
4. large pre-B cell => VDJ rearranged
5. small pre-B cell => VDJ rearranged
6. immature B cell => VDJ rearranged
7. mature B cell => VDJ rearranged

Question 29

Describe the LC rearrangement of the 7 steps of B cell development

Answer 29

1. stem cell => germline
2. early pro-B cell => germline
3. late pro-B cell => germline
4. large pre-B cell => germline
5. small pre-B cell => V-J rearranging
6. immature B cell => VJ rearranged
7. mature B cell => VJ rearranged

Question 30

Describe the surface Ig of the 7 steps of B cell development

Answer 30

1. stem cell => absent
2. early pro-B cell => absent
3. late pro-B cell => absent
4. large pre-B cell => u chain transiently at surface as part of pre-BCR - mainly intracellular
5. small pre-B cell => intracellular u chain
6. immature B cell => IgM expressed on cell surface
7. mature B cell => IgD, IgM made from alternatively spliced HC transcripts

Question 31

Describe the time value wrt to somatic hypermutation(affinity maturation)

Answer 31

affinity maturation increases along with the total number of responses which is generally at 7, 14, 21 days

Question 32

Describe the selection of self-tolerant B cells (4)

Answer 32

1. multivalent self molecule => clonal deletion or receptor editing => apoptosis
2. soluble self molecule => migrates to periphery => anergic B cell
3. Low affinity noncross-linking self molecule => migrates to periphery => mature B cell
4. No self rxn => migrates to periphery => mature B cell

Question 33

Name the 3 steps of a non-positive selection for B cell tolerance (location/action for first 2). How long do these cells live?

Answer 33

1. bone marrow => open repertoire of mature B cells => tolerance induction
2. Blood & 2nd lymph tissues => additional tolerance induction => self-tolerant immature B cells and anergized B cells

If no positive selection occurs then B cells fail to enter lymphoid follicles => B cells have a half-life of about 3 days

Question 34

Name the 4 steps of a positive selection for B cell tolerance (location/action). How long do these cells live?

Answer 34

1. bone marrow => open repertoire of mature B cells => tolerance induction
2. Blood & 2nd lymph tissues => additional tolerance induction => self-tolerant immature B cells and anergized B cells
3. Positive selection => B cells enter lymphoid follicles => recirculate naive B cells for 3-8 weeks
4. Stimulation by antigen => longer lived mature recirculating memory B cells => express high affinity IgG, IgA, IgE

Question 35

What is the order of class switching? Why is this important?

Answer 35

1. IgM
2. IgD
3. IgG
4. IgE
5. IgA

Once class switching occurs, it cannot switch back to another class that is upstream.

Question 36

Describe how the LC is arranged wrt to DNA, RNA and the actions involved

Answer 36

germline DNA: separate V J C gene segments ** somatic recombination **

rearranged DNA: V-J join but C is separate segment transcription

primary RNA transcript: VJ joined but C is separate splicing

mRNA: VJ joined and C joining translation

polypeptide chain: VJC joined to form LC

Question 37

Describe how the LC is arranged wrt to DNA, RNA and the actions involved

Answer 37

germline DNA: separate V D J C gene segments

• somatic recombination => V separate, D-J join, C separate

rearranged DNA: V - D-J join C is separate segment transcription

primary RNA transcript: VDJ joined but C is separate splicing

mRNA: VDJ joined and C joining translation

polypeptide chain: VDJC joined to form HC

Question 38

Describe the steps of B cell development along with its specific location for each step

Answer 38

1. B cell precursor rearranges its Ig genes (attached to BM stromal cell) => generation of BCR in BM
2. Immature B cell bound to self cell-surface antigen removed from repertoire => Neg selection in BM
3. Mature B cell bound to foreign antigen activated => B cells migrate to peripheral lymphoid organs
4. activated B cells give rise to plasma and memory cells => Ab secretion and memory cells in BM and lymphoid tissue