What are Naive B cells?

What types of Igs are expressed on their membranes?

Where does rearragement occur?

What is their life span (range) in the blood stream?

a) B cells that have not encountered antigen

b) expresses mIgm and mIgD

c) rearrangement occurs in the bone marrow

d) short life span when circulating in the blood stream about 3 days to 8 weeks.

1) Start with mature b cells (immunocompetent)

2) Activation of Mature B cells (recognition of ag)

3) Differentiation of activated B cells

- memory

- plasma

During B cell development,

Describe the Antigen-Independent Phase

(maturation)

1) In the bone marrow, CD45R surface marker on the progenitor B cell.

       - VLA-4 attach to VCAM on stromal cell 

2) Pro B cell express C kit (pro b cell) bind to SCF (stromal cell) , Ig alpha and Ig Beta

3) Ig-gene rearragement (selection)

      - heavy chain rearrangement (finalizing)

      - Surrogate light chain

4) Pre B cell with a IL-7 receptor.

5) another surrogate light chain rearrangement to give a variable light and heavy chain that gives an immature B cell that expresses IgM

6) THEN BECOMES NAIVE B CELL, which will move to lymph nodes and spleen with germial centers...which is the beginning of antigen dependent.

During B cell development,

describe the antigen dependent phase.

(activation and differentiation)

GENERAL.

1) Th cells are activated will activate B cells when it is in the periphery. If B cells don't bind will go through apoptosis

2) Once b cells are activated will proliferate in the secondary lymphoid orangas.

3) when bearng high addinity mIG differentiate into plasma and memory cells.

1. Start with a Pro B cell

2. Heavy chain will rearrange from Dh to Jh --> VH to DhJh

3. Rag 1/2 express (p nucleotide addition)

4. TdT express (n nucleotide addition)

What is Ig Rearragement for Pre B cell?

What is Allelic Exclusion?

What is expressed?

a. rearrangement for VlJl

b. only one light chain is expressed on the membrane surface. Surrogate light chain

b. Rag 1/2 Expressed but not Tdt (b/c there is no expression of VDJ in light chain)

1. Explain The expressions of Ig, surrogate light chains and heavy chains that are shown Pro B cell, Pre B cell, and Immature B cell in the bone marrow.

2. What is cross linking and what cross links in the pre b cell and immature b cell? What is the result?

1. Pro B cell: expressed IgA and Ig B

   Pre B cell: express IgA and IgB, VhDhJh with a contant m region (complete H chain) and a surrogate light chain that consists of Vpre B and lamda5 polypeptide
Immature B cell: complete H chain, with an expression of kappa or lambda heavy chain.

2.Crosslinking is one antigen binding to two membrane IgMs causing activation.

Pre B cell: cross linking by stromal cell ligand

     - stop Vh -> DhJh

      - induces variable light and joining light region

Immature b cell: cross linking by antigen.

      - activation or death.

Negative Selection of B cells

How does the Bone Marrow select for useful mature B cells?

- Any cell that expresses anti-self mIg molecules will be forced to apoptosis via Negative selection during maturation in the Bone Marrow

- If it does anti-self mIg molecules, some can undergo light chain editing and move onto maturation of the b cells that will not bind to self-antigen

B2 B cells

Secondary lymphoid organs

B cells come from precursors in bone marrow

V region is highly diverse

Undergoes somatic hypermutation

requires T cell help

high levels of IgG

Possible response to carb antigens

Definite response to protein antigen

Has memory

mIgD on naive B cells

B1 Cells

Periotoneal and pleural cavities

Source is self renewing(comes from existing b1)

V region is restricted in diversity

no somatic hypermutation/no requirement t cell help

high levels of IgM

definite response to carb antigens

possibly respond to protein antigen

little to no memory

little to no surface IgD

What induces thymus dependent (TD) antigens?

What are the two types of Thymus independent antigens?

what does each identify?

No memory formed

1. Type 1 (TI-1) recognizes LPS other bacterial wall components
2. Type 2 (TI-2) recognizes reptitious molecules; flagella
   - IgM usually secreted

TI-1 (mitogen) PRIMARY INFECTION in blood

- activate both mature and immature

- polyclonal

   * activate B cells regardless of Ag specificity

   * LPS = TLR-4
              - divide and Ab release.

- few B cells have BCR's that specifically regonize LPS

     *divide and Ab release

TI-2 SECONDARY INFECTION

- Crosslinking of mIg receptor

- not B cell mitogens

- not polyclonal

- activate mature b cells

- requires t cell cytokines

   *proliferation and isotype switching.

What are the two signals required in a TD antigen?

1. by crosslinking two mIg with a antigen peptide
2. CD40 of b cell ad CD40L on Th cell activate to generate a 2nd signal.

Explain the process for initiating the signaling pathway leading to B cell activation.

1. mIg and Ig a/b with it's ITAM, The Src kinases (blk, lyn, fyn) phosphorylates ITAMs that allow binding of Syk.

2. Phosphorylation creates a docking site for Syk,

3. Syk activates then phosphorylation the Blnk, creating a docking site for PLCgamma2 and BTK.

4. they become phosphorylated to BLNK

1. PIP2 is activated by PLCgama2, BLNK and BTK when it is active and phosphorylated.

2a. DAG -> PKC mediated pathways -> NF kappa beta activation -> NF kappa mediated pathways

2b. IP3 -> release of Ca 2+ from ER -> Ca2+ mediated pathways

3. changes in patterns of gene expression, functional changes in cells, differentiation, activation.

1. syk activate once phosphorylated

2. beginning of BCR signaling complex which activated GEF

3. small G protein pathways either

a. Rho

b. Rac

c. Ras

4. gives changes in patterns of gene expression, functional changes in cells, differentiation, and activation.

C3d, Tapa-1, CD19 and CR2

allows for cascade with a little antigen to enahance the signal.

1. Antigen cross links MIg, generatin a signal.

   - B cell will express B7 and class II MHC

   - endocytosis and presents the antigen on MHC

2. Th cell recognize the class II on b, costimulatory signal (cd 28 and b7)  activates Th cell

3. Th cell express CD40L, B cell express CD40 which interacts and gives 2nd signal

4. B cell express recptors for various cytokines

 - binding od cytokines release Th cell to send signals and support progression of B cell to DNA synthesis and to differentiation.

After stimulation, what is the membrane characterists of the B cell?

What happens after binding occurs when the ILs are bounded to b cell?

a. Expression of IL 2, IL4, and IL5.

b. increase in proliferation and differentiation

- plasma

memory.

1. little membrane Ig; RNA procesing supports secreted Ig

2. Heavy and light chain genes are transcribed at a higher rate than in other cells.

3. memory cells are selected from a similar population of high affinity cells.

During first exposure what Igs are seen?

What about the second exposure?

1. IgM during first exposure is higher

2. second expore is IgG after immunization and concentration increases

What is the site of humoral response?

[image]

paracortex: is where the initial t cell and b cell occurs

Medulla: plasma cell secretion of antibody

germinal center: b cell proliferation and differentiation

primary follicle: b cell activation

What happens at germinal centers?

How many days after exposure?

1. Formation of plasma and memory b cells, class switching, affinity maturation

2. 7-10 days after exposure

What are the cellular events occuring in the germinal centers via light zone and dark zone?

1. B cell enters into germinal center as centroblasts (mature b cell)

2. goes into the dark zone where somatic hypermutation

3. In the light zone selection process via affinity, low   

     affinity -> apoptosis high affinity -> centrocyte

     formation. it checks via follicular dendritic cell forms

     Ag-Ab complex. If centrocyte binds to FDC then it is

     selected for and binds to T helper cells, if not
     then it will go through apoptosis. (POSITIVE SELECTiON)

4. differentiation into memory cell or plasmablasts to a plasma cell.

1. occurs in the light zone of germinal centers, non-dividing centrocte, Ig binds to FDC, CD40 (b cell) binds to CD40L (T helper cell)

What are the ILs for class swithcing into the different Igs?

Be sure to know the proliferation and differentiation cytokines.

[image]

Starts with Activated B cell (centroblasts)

1. IL2, IL,4, IL5 (prolieration cytokines) will proliferate into B cells. (centrocytes)

the following are differentiation cytokines.

2a. IFN-gamma -> Ig2a or IgG3

2b. TGF- beta -> IgA or IGg2B

2c. IL 4 -> IGE or IGG1

2d. IL2, IL4, IL5 -> IgM