Lecture 15: B Cell Activation and Antibody Production II

Question 1

What results in the formation of mRNA for the membrane or secreted form of the u (mu) heavy chain

Answer 1

Alternative processing of primary RNA transcript

Question 2

What results in an increasing fraction of the u protein produced as a secreted form

Answer 2

Ag activation of B cell

Question 3

What are required for somatic hypermutation of Ig V genes to occur

Answer 3

Tfh cells and CD40:CD40L interaction

Question 4

Where does affinity maturation occur

Answer 4

In the germinal center

Question 5

Affinity maturation is a process that occurs through

Answer 5

A repeated process of somatic hypermutation of B cell receptors and subsequent clonal selection

Question 6

Hypermutation can occur where (on gene)

Answer 6

Anywhere along the VDJ region of Ig genes

Can be heavy or light chains or both

Question 7

What is expressed by B cells that initiates somatic hypermutation in the GC, and how does it work

Answer 7

AID
Induces cytosine to uracil deamination
-This is a mismatch that can be repaired by base excision

Question 8

Where do Ig V genes undergo point mutations at a very high rate

Answer 8

In the dark zone of the GC

Can occur at an average rate of almost one per cell division

Question 9

Can Ig V mutations continue to occur in progeny of B cells

Answer 9

Yes, any B cell clone can accumulate more and more mutations during its life in the GC

Question 10

IgG vs IgM # of mutations

Answer 10

IgG has many more mutations

Question 11

Mutations correlate with

Answer 11

Increased Ab affinity for Ag that induced response

Question 12

Why do B cells with highest affinity for Ag have selective advantage

Answer 12

Because they are more likely to bind Ag on FDC which will rescue them from apoptosis

Question 13

Where is a site of tremendous apoptosis

Answer 13

Germinal center, because somatic mutation also generates many B cells that do not express high affinity Ag receptors and die

Question 14

Where do B cells migrate after somatic hypermuation

Answer 14

FDC-rich light zone of the GC

Question 15

Reasons that high affinity B cells survive

Answer 15

• Binding to Ag induces increased expression of anti-apoptotic protein Bcl2
• High affinity B cells will endocytose and present Ag for Tfh cells in GC and induce CD40:CD40L signaling
• Expression of endogenous inhibitors of Fas may occur in high affinity B cells that have bound Ag on BCR

Question 16

What is a primary cause of B cell lymphomas

Answer 16

Translocation of various oncogenes into Ig gene loci

-DNA breaks associated with somatic hypermutation and isotype switching facilitate these translocations

Question 17

Isotype switching primarily occurs where and is facilitated by who

Answer 17

Germinal centers facilitated by Tfh cells

Question 18

Some isotype switching my also occur where and facilitated by

Answer 18

Extrafollicular foci, driven by extrafollicular Th cells

Question 19

Antibody specificity is determined by what region of the Ig chains

Answer 19

Variable regions

Question 20

Intracellular pathogen leading to IgG switching- how does this happen

Answer 20

Intracellular pathogen activate Th1 cells which make IFN-y, which also likely induces IFN-y+ Tfh cells to make more IFN-y
IFN-y induces IgG switching

Question 21

Helminth leading to IgE switching

Answer 21

Helminths likely influence Tfh cell differentiation in to IL-4+ Tfh cells which produce Th2 type cytokines like IL-4 to induce IgE switching

Question 22

B cells in mucosal areas would likely switch to what Ab class- and what would cause this

Answer 22

IgA switching, caused by TGF-b produced by many cells including Treg cells and macrophages

Question 23

What co-stimulates the switch to IgA

Answer 23

BAFF produced by DCs and macrophages

Question 24

Isotype switching and affinity maturation are critically dependent upon ___ which is induced by

Answer 24

AID, which is induced by CD40 engagement from Tfh cells

Question 25

Immunodeficiencies related to CD40-CD40L might cause what Ab to dominate

Answer 25

IgM, because class switching wont occur without CD40/CD40L and AID

Question 26

Every C gene is preceded by a ______ that controls rearrangement process

Answer 26

Switching sequence

Question 27

AID switches C to U, and then what happens

Answer 27

UNG removes U residue, then endonuclease APE1 creates nicks that lead to DS breaks- probably fixed by NHEJ

Question 28

CSR is preceded by

Answer 28

Expression of germline transcripts which open the chromatin structure of a specific S region and make it accessible to the recombinase

Question 29

Switch regions are comprised of

Answer 29

Repetitive sequences of palindrome rich motifs and result in looped out deletions

Question 30

Short lived plasma cells are generated in

Answer 30

Extrafollicular compartments during T-independent responses | -may also be generated early during T-dependent responses in extrafollicular B cell foci

Question 31

Short lived plasma cells typically found where

Answer 31

In secondary lymphoid organs or peripheral non-lymphoid tissues

Question 32

Long lived plasma cells are generated

Answer 32

In T-dependent responses to protein Ag in the GC | -Signals from BCR and IL-21 are involved via stage of their precursors called plasmablasts

Question 33

Plasmablast to long lived plasma cell route

Answer 33

Generated in GC and home to one marrow where they differentiate into long lived plasma cells

Question 34

Long lived plasma cells are maintained by

Answer 34

BAFF

Question 35

% of Ab in blood produced by long lived plasma cells

Answer 35

50%

Question 36

B cells generated in the bone marrow exit as _____ which are ____ and express ____

Answer 36

Exit as pre- B cells which are immature and express IgM | -They further mature into naïve B cell and then follicular or MZ B cells in the spleen

Question 37

Activated (T-independent) MZ and Follicular B cells turn into

Answer 37

Plasmablasts and short lived plasma cells

Question 38

Activated (T-dependent) MZ and F B cells turn into

Answer 38

Memory B cells, and express Abs of switched class/higher affinity

Question 39

When is a long lived plasma cell formed

Answer 39

When memory B cells are reactivated by Ag

Question 40

Long lived plasma cells survive where

Answer 40

In the bone marrow mostly, but also secondary lymph organs

Question 41

Do memory B cells still require Tfh cell-mediated regulation following Ag recall?

Answer 41

Yes, Ag specific memory Tfh cells likely still regulate memory B cells responses

Question 42

What may stimulate Ab production in the absence of Th cells (TI responses)

Answer 42

Non-protein Ags such as polysaccharides or lipids

Question 43

What Abs are produced in the absence of Th cells

Answer 43

Low affinity IgM mainly, also some IgG and IgA

Question 44

What makes TI Ags able to stimulate B cell activation without T cell help

Answer 44

Many TI Ags are multivalent, and induce maximal cross-linking of the BCR complex on B cells, leading to activation without T cell help

Question 45

Which B cells are especially important for response to TI Ags

Answer 45

MZ B cells and B-1 B cells

Question 46

MZ B cells are a distinct population of B cells in the ___ that mainly respond to _____ and differentiate into

Answer 46

In the spleen, respond to polysaccharides and differentiate into short lived plasma cells that produce mainly IgM

Question 47

B-1 B cells respond to TI Ags mainly where

Answer 47

Peritoneum and mucosal sites

Question 48

TI Ags cannot be processed and presented by

Answer 48

MHC molecules, and therefor cannot be recognized by CD4+ helper T cells

Question 49

Polysaccharides activate ____ system by the _____ pathway, leading to

Answer 49

Activate compliment system by the alternative pathway, generating C3b and then C3d which is recognized by CR2 on B cell

Question 50

Two ways B cells can be activated without T cell help

Answer 50

- Compliment coated Ags can ligate both BCR and CR2 | - Simultaneous PAMP recognition and TLR signaling

Question 51

Cytokines produced by ____ may stimulate isotype switching in TI responses. Examples

Answer 51

Non-T cells - TGF-b secreted at many mucosal sites causes IgA - BAFF produced by DCs/MOs induces AID

Question 52

What contributes to the generation of natural antibodies, what are they and who generates them

Answer 52

TI Ags They are low affinity anti-carbohydrate Abs Produced by B-1 cells in GI tract and MZ B cells in spleen

Question 53

Memory occurs only if vaccines are able to activate

Answer 53

T helper cells

Question 54

How are vaccines to capsular polysaccharides produced (as they do not stimulate T cells)

Answer 54

Polysaccharide is linked to a foreign Ag

Question 55

What happens when Ab-Ag complex simultaneously bind BCR and the FcyRIIB receptor

Answer 55

FcyRIIB associated phosphatases inhibit signaling by the BCR complex and block B cell activation

Question 56

IgG vs IgM and FcyRIIB activation

Answer 56

IgM activates complement but do not bind to FcyR are involved in amplification, while IgG leads to feedback

Question 57

FcyRIIB knockout mice show

Answer 57

Uncontrolled Ab production