Humoral Immunity

Question 1

What happens to blood-borne antigens?

Answer 1

They are captured by marginal zone macrophages in the spleen and transferred to marginal zone B cells or follicular B cells without processing.

Question 2

What happens to antigens in the GI tract?

Answer 2

They are transported through M cells to follicular B cells and B1 cells in lamina propria

Question 3

What is cross-linking?

Answer 3

When 2 BCR molecules bind to the same antigen to activate a B-cell.

Question 4

What are the additional signals for B cell activation?

Answer 4

CR2, TLR or a helper T cell

Question 5

How can you tell if a B cell is activated?

Answer 5

It is proliferating

Question 6

How can C3d help activate a B cell?

Answer 6

C3d binds to the CR2 along with antigen, causing cross-linking.

Question 7

When is IgM released?

Answer 7

Early phase of humoral immune response

Question 8

Describe the interactions between Th1/2 or reg’s TCR and a B cell’s BCR.

Answer 8

1. If Th1 binds to a B cell, Th1 secrets IFN-y and causes isotype switching to IgG.
2. If Th2 binds to a B cell, Th2 secrets IL-4 and causes isotype switching to IgE.
3. If Treg binds to a B cell, Treg secrets TGF-B and causes isotype switching to IgA.

Question 9

Which Immunoglobulins can be secreted?

Answer 9

IgG, A, and E are secreted. IgM can be membrane bound or secreted. IgD is only membrane bound.

Question 10

During isotype switching, what part of the Ig is changed? What does that entail?

Answer 10

The Fc region of the heavy chain of the antibody is changed; It alters the function of the antibody, NOT what it can bind to.

Question 11

What enzyme performs the isotype switching?

Answer 11

Activation induced deaminase (AID), NOT RAG

Question 12

Do all B cells isotype switch?

Answer 12

NO

Question 13

What do B-cells do after interacting with a Th cell?

Answer 13

(After isotype switching); Change their chemokine receptors again and go back to the follicle with the Th cell.
2. Form a germinal center making it a secondary follicle.

Question 14

What is happening in the Dark zone of a germinal center?

Answer 14

B cells are undergoing somatic hypermutation; Changing the variable regions of the heavy and light chains. This process is also dependent on AID as it makes higher affinity antigens.

Question 15

What is happening in the Light zone?

Answer 15

Follicular dendritic cells present antigens to B cell with their new antibodies; Positive selection

Question 16

After surviving positive selection, what can happen to a B cell?

Answer 16

It can differentiate into a plasma cell or a memory cell.

Question 17

Describe the life span of a plasma cell if it was made inside or outside the germinal center.

Answer 17

If made in the germinal center, it will migrate to the bone marrow and make antibodies for months to years.
If made outside the germinal center, it will stay in the secondary lymphoid organs and make antibody for a few weeks.

Question 18

Describe memory b cells

Answer 18

Circulate in the blood and lymphoid organs; Long-lived. Will divide and differentiate if activated by antigen.