Lecture 14

Question 1

Can B cells recognize Ags without processing?

Answer 1

Yes!

Question 2

If the Ag is a non-protein polysaccharide what will the primary response be?

Answer 2

Primary response: Non-protein Ag (polysaccharide)

IgM > IgG

Question 3

If the Ag is a protein what will the secondary response be? Does it need a helper T cell?

Answer 3

Secondary response: protein Ag
Need helper T-cell
IgG > IgM

Question 4

What 2 types of B cells are there? Which ones are T-independent, T-dependent, or both? If both, which ones are which?

Answer 4

B cells can become either B1 or B2 lineages
B1 lineages are only T-independent
B2 lineages can be either T-Dependent or T-Independent
T-Dependent B2 cells are Follicular B cells
T-Independent B2 cells are Marginal Zone B cells

Question 5

Without the help of CD4+, how are B cells limited? What will they not form? Which Ig will they produce? What type of Ag will they only recognize?

Answer 5

**Without the help of CD4+ T cells, differentiation is limited (not likely to form memory cells, usually IgM only, recognition of non-protein)

Question 6

Where are B1 cells produced and where?

Where are they found later in life?

Answer 6

Only produced early in life (fetal liver)

Sits in tissue (GI/Lungs)

Question 7

When are B2 cells produced? Where are they found later in life?

Answer 7

Produced throughout adulthood (continuously replaced)

Widespread- found in many places in the body

Question 8

During T-Dependent Follicular B2 cell activation, where do the B cells migrate to and what guides them there?

Answer 8

B-cells migrate to lymphoid follicle (B-cell rich zone) in lymph node
-Guided by FDC (Follicular DC):

Question 9

During T-Dependent Follicular B2 cell activation, what are the 3 characteristics of Follicular DCs? Where are they found, do they express MHC? What do they secrete?

Answer 9

i. Only present in LN, (do not migrate into periphery)
ii. Do not express MHC I or II (do not process antigen)
iii. Secrete CXCL13 Selectin (binds CXCR5 on B cells) and can hold onto the Ag for B cell activation (immune complex formation)

*Note that FDCs use Selectins to attract B cells, NOT chemokines

Question 10

What are the 3 possibilities for BCR-Ag recognition to occur?

Answer 10

2 BCR receptors
BCR + CR2
BCR or TLR

Question 11

Do the B cells process the Ag after they recognize it from the FDC?

Answer 11

Yes

Question 12

During T-Dependent Follicular B2 Cells Activation, what are the 4 results of activating B2 cells?

Answer 12

i. Expression of survival proteins (as well as BAFF)
ii. Ag presentation
iii. Increased cytokine receptor expression
iv. Increased expression of CCR7 (migration from follicle to T cell rich zone)

Question 13

During the Germinal Center Reaction, where will activated B cells migrate to? What 2 things occur here?

Answer 13

Activated B cell will migrate to dark

• Isotype switching
• Somatic hypermutation of Ig (V) genes

Question 14

During the Germinal Center Reaction and after migrating through the dark zone, where will activated B cells migrate to? What will they interact with here? What is the binding that occurs in this zone and what is released?

Answer 14

Migrate to light zone and interact with T Follicular Helper cells
ICOS and CD40L binding and IL21 release

Question 15

What is the overall effect of the germinal center reaction?

Answer 15

Highest affinity receptor

Undergoes positive selection –> memory or plasma cell

Question 16

How are antigens captured during the T-Independent activation of Marginal Zone B2 Cells? What cells recognize the antigen and where are they located? What receptors are used to recognize these antigens? What cells deliver the Ags to the Marginal zone B2 cells?

Answer 16

Marginal zone macrophage resident cells (BCR-TLR)

-Plasma Dendritic Cells deliver Ag’s to Marginal zone B cells

Question 17

During the activation of Marginal B2 cells in a T-independent manner, what 4 cytokines are produced? Activation of Marginal Zone B2 cells lead to the differentiation into what 2 Ig? The production of these 2 Ig causes what to the activation threshold? How is this reponse compared to follicular B cells?

Answer 17

Cytokine production (BAFF, IL6, IL10, Type I IFN)

Differentiation into IgM and IgG

• LOWER Activation threshold!
• More rapid response compared to follicular B cells