B cells

Question 1

What components of the innate immune system recruit the adaptive system?

Answer 1

• dendritic cells

- complement cascade -macrophages

Question 2

What do B cells do?

Answer 2

• make Abs that mark pathogens for destruction

- recruit other cells and molecules that destroy pathogens

Question 3

Abs circulate as a component of _____ in blood and lymph.

Answer 3

plasma

Question 4

Name 4 functions of Abs:

Answer 4

• neutralization of toxins/viruses/bacteria
• opsonization of bacteria
• activation of compliment cascade (classical pathway)
• help activate specialized cells in response to antigen

Question 5

Describe IgG:

Answer 5

• major serum Ig (75%)
• small size i.e. diffuses easily from blood to tissues
• subclasses of IgG have diff roles: 1. opsonization 2. activation of compliment

Question 6

Describe IgM:

Answer 6

• first Ab produced in immune response
• pentameric (binds strongly)
• BIG; doesn’t diffuse from blood (stays in circulation)
• no receptor for IgM Fc on phagocytes/leukocytes (doesn’t directly recruit these)
• IgM Fc can bind and activate compliment

Question 7

Describe IgA:

Answer 7

• predominates in secretions
• dimeric; protects the surface of respiratory + intestinal tracts
• poor opsonin
• weak compliment activator

Question 8

Describe IgE:

Answer 8

• trace amounts in serum
• mostly bound to surface of mast cells via Fc (beneath skin mucosa)
• binds Ag–> release of mast cell granules: inflammatory mediators–> trigger cough, sneezing, vomiting (all to expell pathogen)

Question 9

The molecular process through which B cells are able to detect infinite, specific antigens and create specific antibodies is called _______.

Answer 9

somatic recombination

Question 10

What order do the following happen?

immature B cell, heavy chain rearrangement, first checkpoint, second checkpoint, early pro-B cell, light chain gene rearrangement

which of these makes functional IgM??

Answer 10

order:

• early pro-B cell (committed)
• heavy chain gene rearrangement
• first checkpoint (selects functional heavy chains)
• light chain gene rearrangement
• second checkpoint (selects functional light chains)
• immature B cell (makes IgM)

Question 11

What immunoglobulin serves as the receptor on new B cells?

Answer 11

IgM

Question 12

Only B cells that do not recognize self-antigen are allowed to leave the bone marrow for the peripheral circulation. What regulatory process allows for this?

Answer 12

Tolerance (death by apoptosis, inactivation)

Question 13

Where do B cells encounter antigen?

Answer 13

Secondary lymphoid tissue. Here they complete development/differentiation to plasma cells.

Question 14

What is secondary lymphoid tissue?

Answer 14

• lymph nodes
• spleen
• gut-associated lymphoid tissue

Question 15

What part of the lymph node is the ‘B cell area’ located?

The T cell area?

Answer 15

Cortex

Cortico-medullary area

Question 16

What 3 things are necessary for B cell activation?

Answer 16

1. cross-linking of surface Ig w specific Ag
2. association of B cell receptor w B cell co-receptor (CDx)
3. additional signals provided by CD4 helper T cells (Th); Th expresses CD40 ligand detected by B cell….Th secretes cytokines that activate B cell (plasma cells that secrete Ab)

Question 17

What happens to B cells in the T cell zone?

Answer 17

• interact with Ag
• interact with Th cells of same Ag-specificity
• conjugate pairs form
• activation of B cells to plasma cells

Question 18

Where is the primary focus for clonal expansion of Ah-activated B cells?

Answer 18

Medullary cords

Question 19

Do all B cells require Th to differentiate into Ab-producing plasma cells?

Answer 19

No.

Question 20

Where is the secondary focus for clonal expansion of Ag-activated B cells?

Answer 20

The germinal centre (cortex)

Question 21

What is in the germinal centre?

Answer 21

• activated B cells
• Th cells
• Ag (carried by follicular dendritic cells- FDC)

Question 22

What is the difference bw the roles of the primary focus and secondary focus?

Answer 22

Primary: leads to early secretion of specific Ab and provides early protection against infx.

Secondary (germinal centre): provides more effective, later response for persistent infx and re-infx. Dependent on Th cells to refine Ab response.

Question 23

Mutations occurring in the B cell receptor gene during proliferation in the germinal centre can increase their affinity for Ag. What is this process called? What is allowing for rapid division?

Answer 23

Somatic hypermutation.

Cytokine microenvironment of the germinal centre.

Question 24

Only B cells that have the highest affinity for Ag are given survival signals in the germinal centre. What is this called?

Answer 24

Affinity maturation.

Question 25

When do germinal centres present in lymph nodes? What happens to the lymph nodes (seen clinically)?

Answer 25

~ 1 week post-infx swelling of lymph nodes

Question 26

What determines isotype switching (from IgM to other Igs: IgE, IgA, IgG)? What region undergoes recombination during isotype switching?

Answer 26

- T cell interaction with B cell - microenvironment -C genes recombine (V regions stay the same)

Question 27

What compounds result in centrocytes becoming 1. plasma cells versus 2. memory B cells?

Answer 27

IL-10 : plasma cells (make Ab, fight current infx) IL-4: memory B cells (future)

Question 28

List differences bw resting B cells and plasma cells.

Answer 28

B cell: has surface Ig, surface MHC II, lower rate Ig secretion, growth inducible, somatic hypermutation possible, isotype switching possible.

Question 29

Name 2 types of B cell malignancies:

Answer 29

- multiple myeloma (arises from plasma cells in BM) | - leukemia (CLL-chronic lymphocytic leukemia)

Question 30

List 2 B cell activation and survival factors.

Answer 30

- BAFF (excess in SLE, high Ab) | - APRIL

Question 31

Name a Rx for lupus that relates to B cell survival factors:

Answer 31

Anti-BAFF antibody

Question 32

APRIL, BAFF + TACI= APRIL + BCMA= BAFF + BR3 =

Answer 32

B cell activation Bone marrow plasma cell survival Naive B cell survival

Question 33

Where is IgA secreted by plasma cells? How does it get from the basal end of epithelial cells to the apical surface?

Answer 33

Just under the epithelial BM. By binding to poly-Ig receptors.

Question 34

What receptor on erythrocytes do C3b-Ab-Ag complexes bind to for clearance from circulation? Where are the complexes taken>

Answer 34

CR1 receptor on erythrocytes. Taken to; liver + spleen where pahgocytotic cells remove the immune complexes.

Question 35

Immune complex mediated disease, due to circulating immune complexes that activate compliment in tissues/vessels, include

Answer 35

- vasculitis - arthritis - glomerulonephritis in the kidney

Question 36

Low levels of C3 and C4 in serum indicates _________

Answer 36

compliment consumption (immune complex mediated disease)

Question 37

What are the most effective Abs at activating compliment?

Answer 37

IgM and IgG3