EXAM 2 B Cells: Development

Question 1

what are the 6 B cell life phases? Where do they occur?

Answer 1

Bone marrow:

1. repertoire assembly
2. negative selection
3. positive selection

Periphery:

4. searching for infection
5. finding infection
6. attacking infection

Question 2

is there a stockpile of B cells?

Answer 2

no, they are not stockpiled but instead constantly replaced

• 30 billion per day
• mature half-life of 50-100 days

the vast majority of B cells will die before they reach maturation

Question 3

populations of B cells ___ at each life phase

Answer 3

winnow

ie. populations are reduced; nonfunctional or dysfunctional B cells are destroyed

Question 4

describe the lineage of pro-B cell development during the first 3 phases in the bone marrow

Answer 4

Question 5

describe the lineage of B cell development during the second 3 phases once it reaches secondary lymphoid organs and circulation

Answer 5

Question 6

fill out this chart for immature B cell development

Answer 6

Question 7

how do stromal cell interactions drive B cell development?

Answer 7

• **don’t need to know any of the factors**
• **this is positive selection**
• stromal cells express adhesion molecules and growth factors
• B cell receptor expression changes with progression through developmental stages
• pro-B cells are programmed to die in the absence of survival signals
• CCL21 expressed by stromal cells
• BAFF released by dendritic cells to stimulate immature B cells to become mature

Question 8

describe heavy chain rearrangement in pro-B cells

Answer 8

• early pro-B cell
  
  • RAG proteins activated
  • heavy chain D and J segments joined
  • occurs on both chromosomes
• late pro-B cell
  
  • heavy chain V and DJ segments joined
  • occurs subsequentially on chromosomes
  • two chances for rearrangement

Question 9

___ signaling causes the transition from pro to pre-B cell

Answer 9

pre-BCR

Question 10

how does pre-BCR signaling cause the transition from pro to pre-B cell?

Answer 10

• VDJ rearrangement produces pre-BCR
• pre-BCR expressed in the ER
• surrogate light chain expressed
• Ig alpha/beta expressed

Ig beta signaling:

• checkpoint clearance
• turns off RAG proteins
• initiates cell division
• allelic exclusion - a functional heavy chain is produced by only one chromosome

Question 11

pre-B cell light chains are rearranged ___

Answer 11

sequentially

Question 12

describe pre-B cell light chain rearrangement

Answer 12

• sequential
• 4-5 recombination attempts possible per chromosome
• kappa then lambda
• approximately 85% of small pre-B cells survive
• functional antibody expressed on the cell surface

Question 13

___ ensure immunoglobulin integrity

Answer 13

checkpoints

Question 14

describe how checkpoints ensure immunoglobulin integrity

Answer 14

Question 15

describe B cell maturation and immunoglobulin expression

Answer 15

Question 16

describe how immature B cells undergo negative selection

Answer 16

• exposure to self antigen ensures tolerance
  
  • an inability to respond to self antigen (aka the ability to not respond to self antigen…)
    
    • central tolerance (bone marrow) and peripheral tolerance (periphery)

Question 17

what are the 3 fates of B cell negative selection?

Answer 17

• light chain reorganization
• apoptosis
• anergy - cells that are still alive but signaling and activating processes are shut down; they eventually die

Question 18

immature B cells migrate to ___

Answer 18

lymphoid tissues

Question 19

what are the 3 secondary lymphoid tissues?

Answer 19

spleen, lymph nodes, and GALTs

Question 20

describe the maturation of B cells within secondary lymphoid tissues

Answer 20

• HEV - high endothelial venule
• FDC - follicular dendritic cell
• PF - primary follicle
• BAFF - B cell activating factor (immature to mature)
• LT - lymphotoxin

positive selection:

• lymph node localization
• BAFF signaling
• increased IgD expression, decreased IgM expression

Question 21

B cells are activated in ___

Answer 21

lymphoid tissues

Question 22

describe how B cells are activated in lymphoid tissues

Answer 22

Question 23

what are polyclonal antibodies?

Answer 23

multiple antibodies targeted against the same antigen

Question 24

what are monoclonal antibodies?

Answer 24

a single antibody targeted against a single antigen

Question 25

how are antibodies used diagnostically and therapeutically?

Answer 25

• diagnostic
  
  • pathogen identification
  • cellular identification
  • protein quantification
• therapeutic
  
  • targeted killing
  • chemical delivery
  • immunomodulatory

Question 26

dysfunctional B cell development causes ___

Answer 26

cancers

Question 27

no allelic exclusion would give ___ B cell receptors with ___ binding

Answer 27

• heterogenous
• low-avidity
• the point of allelic exclusion is to make sure that a functional heavy chain is produced by only one chromosome
• if there is no allelic exclusion, heavy chains will be produced by the paternal chromosome, maternal chromosome, and a mixture of the two, so it would reduce the specificity of that B cell

Question 28

B cell negative selection occurs in the ___, and positive selection occurs in the ___

Answer 28

• bone marrow
• periphery

Question 29

___ prevents immediate reinfection by a pathogen that the immune system has already been exposed to

Answer 29

memory B cells

Question 30

at what developmental stage do B cells express both IgM and IgD?

Answer 30

mature naive B cell

Question 31

at what stage is the light chain rearranged?

Answer 31

small pre-B cell

Question 32

what occurs between the large pre-B cell and small pre-B cell developmental stages?

Answer 32

• cell division
  
  • 100 small pre-B cells
  • RAG genes reactivated
  • unique recombination per cell
• after heavy chain rearrangement, all of the large pre-B cells in that group will have the same heavy chain; light chain rearrangement can be different for every B cell in that group, so it introduces even more diversity

Question 33

what happens during the two stages of heavy chain rearrangement?

Answer 33

• early pro-B cell:
  
  • RAG proteins activated
  • heavy chain D and J segments joined on both chromosomes at once
• late pro-B cell:
  
  • heavy chain V and DJ segments joined sequentially on chromosomes
  • 2 chances for rearrangement
  • 50% signaled to die by apoptosis, 50% signaled to survive and become pre-B cells

Question 34

what are the two main functions of the surrogate light chain?

Answer 34

• after heavy chain rearrangement, it binds to the heavy chain and acts as a placeholder protein to ensure that the new light chain will be able to bind the heavy chain
• allows the heavy chain to bind Ig beta and Ig alpha

Question 35

at what B cell developmental stages are the two checkpoints, and what is the function of each checkpoint?

Answer 35

• 1st checkpoint between late pro-B cell and large pre-B cell (aka after heavy chain rearrangement)
  
  • expression of functional (productive rearrangement) or nonfunctional (nonproductive rearrangement) heavy chain
• 2nd checkpoint between small pre-B cell and immature B cell (aka after light chain rearrangement)
  
  • expression of functional (productive rearrangement) or nonfunctional (nonproductive rearrangement) antibody on cell surface

Question 36

describe the 3 steps of B cell negative selection

Answer 36

occurs in the bone marrow

• 1: light chain reorganization
  
  • self antigen ligates immature B cell’s IgM
  • immature B cell continues to rearrange light-chain genes
  • immature B cell makes a new light chain and thus an IgM with a different specificity
• 2: apoptosis
  
  • if the new receptor is self reactive, light chain genes continue rearranging
    
    • successive new receptors are now self-reactive. no further rearrangements are possible and apoptosis occurs
  • if the new receptor is not self-reactive, the B cell leaves the bone marrow
• 3: anergy
  
  • IgM of immature B cell binds soluble univalent self antigen
  • B cell is signaled to make IgD and become unresponsive to antigen
  • enters peripheral circulation and doesn’t survive long