Lecture 15

Question 1

Where are membrane-bound antibodies found?

Where are secreted antibodies found? What can these become and eventually develop into?

Answer 1

Membrane-bound found in LN and spleen

Secreted is found in the bloodstream

• Become short-lived plasma cell
  - Can become memory cells

Question 2

What are the membrane-bound Ig?

Answer 2

IgM/IgD only membrane-bound BCRs

Question 3

Can IgM be secreted? If so, how?

Answer 3

IgM can also have secreted form

-Loses its tail piece and TM segment

Question 4

What is the membrane-bound or secreted form dependent on? What type of secreted protein do activated B cells increase?

Answer 4

Form is dependent on alternative processing of primary RNA

-Activated B cells increase the amount of secreted µ protein

Question 5

What 3 structures are found on secreted antibodies? Describe the 2 regions secreted Ig contain.

Answer 5

Heavy and light chains

Fc region
-Effector region (determines activity)

Fab region

• Ag binding fragment
• Comprised of both heavy and light chain
• Contains CDR which are varied mutations to give specificity

Question 6

Where does class switching occur on the Ig? Which region is actually being changed?

Answer 6

Occurs with the Heavy chain

-Changes of the constant region

Question 7

Where does class switching occur? What does it require? Is there a change in Ab specificity?

Answer 7

Occurs in germinal centers of the LN
Requires T follicular helper cells
NO CHANGE IN AB SPECIFICITY

Question 8

Which Ig does IFNy stimulate? What 2 things is this Ig used for?

Answer 8

INF-y - -> IgG

Used for opsonization of phagocytes, complement activation

Question 9

Which immunoglobulin does IL4 stimulate? For immunity from what? What does this Ig contribute to?

Answer 9

IL-4 - -> IgE
Immunity from helminths
Allergies

Question 10

Which immunoglobulin do TGF-Beta and BAFF stimulate? For what kind of immunity?

Where does TGF-Beta come from?
Where does BAFF come from?

Answer 10

TGF-Beta, BAFF - -> IgA
-Mucosal immunity
Note* TGF-Beta comes from Treg cells and Macrophages
Note* BAFF comes from DCs and Macrophages

Question 11

Interactions between what induces Activation Induced Deaminase (AID)? Note what cell each receptor is found on. What is process AID required for?

Answer 11

CD40 on APCs (ex. B cells)

CD40L on T cells

Interactions induces AID (THIS IS REQUIRED FOR CLASS SWITCHING)

Question 12

What cell activates Class Switching Recombinase? To which region (variable or constant) does this work in? What specific genes does it change?

Where is the switch (S) sequence found?

What 3 molecules work together to splice and loop out DNA at the S sequence?

Answer 12

In cells activated by Tfh cells

Changes Cµ/∂ gene to other C-heavy gene

Switching (s) sequence in front of each heavy chain gene

AID, UNG, APE1 work to splice and loop out DNA at the S sequence - -> piece of DNA is excised to specific new heavy chain gene

Question 13

Describe the mechanism of action for Class Switching.

Answer 13

Tfh -> CD40: CD40L -> AID -> (Cytosine -> Uracil) -> UNG -> APE1

Question 14

For class switching, describe the functions for each of the following molecules:

Tfh
CD40:CD40L
AID
Cytosine -> Uracil
UNG
APE1

Answer 14

Tfh cell presented to by B cell -> Induces CD40L expression

CD40 on B cells binds to CD40L on T cell

CD40:CD40L interaction induces the production of AID

AID deaminates cytosines

UNG removes Uracils

APE1 endonucleases make nicks to cause looping out of the DNA and remove part of the sequence

Question 15

In what type of activation does B cell affinity maturation occur?

Answer 15

Only occurs in B cells activated by T-cell dependent Ags

Question 16

For affinity maturation of B cells, where does the mutation occur in? How many mutations per cell division?

Answer 16

Causes mutations in the variable region that allow the Ab to bind stronger

• One mutation/cell division
• Occur in V (variable) region* typically in Ag-binding

Question 17

In what zone does affinity maturation occur in?

Answer 17

Light zone

Question 18

Describe affinity maturation in terms of availability of Ag. What kind of B cells will bind to Ag first?

What 2 mechanisms protect B cells from apoptosis?

Answer 18

As Ag is eliminated, less available in GC -> B cells with high affinity to Ag will bind first

• Other weaker B cells will undergo apoptosis via Fas:FasL
• High affinity activated CD40:CD40L signaling and Fas inhibitors (protects from apoptosis)

Question 19

What occurs in the dark zones and the light zones of the germinal center?

Answer 19

Dark Zones- Somatic Hypermutation and Proliferation

Light Zones- Affinity Maturation via FDC and Class Switching via Tfh cells
-Where apoptosis of many B cells occurs due to the lack of affinity for Ag

Question 20

Where do lymphomas (B cell tumors) develop? Why?

Answer 20

Lymphomas ( B cell tumors) develop in GC

Higher risk of this here because somatic hypermutation and isotype switching

Question 21

What can somatic mutation also cause within the dark zone of the germinal center?

Answer 21

Autoimmunity

-Somatic mutation defect can produce self-reactive B cells

Question 22

What are plasma cells and what are the two types?

Answer 22

Terminally differentiated B cells -> LOTS of Ab

Short lived
Long lived

Question 23

Describe short lived plasma cells. Where are they generated/do they require T cells? Where are found after they are generated?

Answer 23

Generated in extrafollicular compartments in T-INDEPENDENT response

Found in the secondary lymph nodes

Question 24

Describe long live plasma cells. Do they require T cells? What kind of Ag do they respond to? What 2 signals are required to generate long lived plasma cells. What signal maintains them? how long can they live? How long does it take to mature after immunized at the doctors office?

Answer 24

Generated in T-DEPENDENT repsonse

- To protein Ag - Generated by signals from BCR and IL-21 - Maintained by BAFF - Lives months to years - Occurs 2-3 weeks post immunizations

Question 25

Long lived plasma cells constitute about how many of the Abs found in healthy adults?

Describe the pathway for differentiation of long lived plasma cells? **Make sure to note where they reside for good when they are fully mature

Answer 25

-Constitutes 50% of Abs in healthy adults

In GC (plasmablasts) -> enter circulation -> bone marrow -> differentiate

Question 26

Where are memory B cells generated and in response to what?

Answer 26

Generated in GC in response to T-dependent Ags

Question 27

What protein does memory cells express high amounts of?

What other 2 structures do memory B cells express high levels of?

Answer 27

Express HIGH Bcl-2
-Anti-apoptotic protein

Express high affinity BCR and switched isotypes

Question 28

For memory cells, compare primary and secondary response to Ab production in terms of speed? Do memory B cells require helper T cells?

Answer 28

Allows faster Ab production in secondary exposure to Ag cells
-Still require Th cell mediated regulation just works faster than in naïve B cells

Question 29

Where are memory B cells located?

Answer 29

Some remain in LN, others circulate

Question 30

What do T-Independent B cells react to? What do they activate? How are these B cells activated? (think of the previous question)

Answer 30

Any non-protein Ag (MAJOR MECHANISM FOR IMMUNITY TO ENCAPSULATED BACTERIA)

Often activate complement (alternative) -> C3b to C3d which binds CR2 on B cells

Question 31

What kind of Abs do T-Independent B cells produce? What kind of affinity maturation do they have?

What kind of Ig do they produce? Describe the diversity of this Ig’s isotype switching.

Most ags that activate the T-independent B cells are multivalent. What does this allow for B cells?

Answer 31

Abs produced here are low affinity (little affinity maturation)

Mostly IgM
-Limited isotype switching

Most are multivalent
-Allows cross linking which gives strong enough response to forego T cell interaction

Question 32

Where are T-Independent B cells activated? What can they differentiate into?

Answer 32

Occur in marginal zone in B1 cells

Can persist to short lived plasma cells (IgM only)

Question 33

Effective vaccines require ____ __ cell formation.

This only occurs if the vaccines can activate what?

Answer 33

Effective vaccines require memory B cell formation

Only occurs if vaccine can activate T helper cells

Question 34

If vaccines can only work if they can activate helper T cells, what about vaccines that work on TI Ags? What are the polysacchrides linked to? What does this induce? Give an example of a vaccine that does this.

Answer 34

Polysaccharides are linked to foreign PROTEIN -> Hapten carrier conjugate

Induce high affinity Abs and memory cells for capsular polysaccharides

Ex. Pneumococcal Vaccine

Question 35

Describe FcyRIIB. What portion of the Ab can it bind to?

When FcyRIIB binds, that signal does it initiate? What doe this lead to?

Answer 35

Receptor that can bind the Fc portions of Ab
-Allows Ag-Ab complexes to bind

Binding initiates signal -> production of phosphatases that inhibits B cell activation

Question 36

What does FcyRIIB tell B cells to inhibit B cell activation? What kind of Abs dose this occur in? *What are the effects of the Complement Activation while this is going on?

Answer 36

Inhibition of B cell activation

• Tells B cells that enough Ab has been produced and to stop producing the Ab
• Self regulation
• This only occurs in secreted Ab

Note* Complement activation still activates an Ab response