Chapter 7: Humoral immune responses

Question 1

What are the possible outcomes of activated B cells after differentiation?

Answer 1

• antibody secreting plasma cell
• IgG-expressing B cell
• High-affinity Ig-expressing B cell
• memory B cell

Question 2

How are B cells activated?

Answer 2

• helper T cells
• other stimuli

Question 3

What happens during T-dependent B cell activation?

Answer 3

• protein antigen binds to follicular B cell
• helper T cell binds via MHC molecule
• isotype-switched, high-affinity antibodies
• memory B cells and long-lived plasma cells are formed

Question 4

What happens during T-independent B cell activation?

Answer 4

• polysaccharide antigen binds to IgM antibody on marginal zone B cell (in spleen)
• other signals activate it (complement proteins, microbial product)
• low affinity antibodies
• short-lived plasma cells are formed

Question 5

What is the lag, peak response, antibody type, and affinity of a primary response?

Answer 5

lag: 5-10 days

peak response: small

antibody type: IgM>IgG

low affinity and more variable

Question 6

What is the lag, peak response, antibody type, and affinity of a secondary response?

Answer 6

lag: 1-3 days

peak response: large

antibody type: mostly IgG or maybe IgA or IgE under certain situations

high affinity

Question 7

What decides the antibody type and affinity?

Answer 7

• response to protein antigens
• if a first or second infection

Question 8

Where are naive B cells located?

Answer 8

peipheral lymphoid tissue

Question 9

How many receptors must be bound to antigens in order for antigen receptor-mediated signal transduction in B cells?

Answer 9

2 or more

Question 10

What completment receptor and complement product binds to activate B cells?

Answer 10

complement receptor (CR2) binding by 3Cd bound to microbe

Question 11

What receptor binds to the PAMP from microbe to activate B cells?

Answer 11

Toll-like receptor

Question 12

What product of the complement system binds to CR2 to activate B cells?

Answer 12

C3d

Question 13

What are the functional consequences of antigen receptor-mediated B cell activation?

Answer 13

• increased survival and proliferation
• interaction with helper T cells
• responsiveness to cytokines
• migration form follicle to T cell zone
• antibody secretion

Question 14

What does CCR7 and CXCR4 do to T cells?

Answer 14

CCR7
- increases to go to T cell zone
CXCR4
- decreases this to go to B cell

Question 15

What does CCR7 and CXCR4 do to B cells?

Answer 15

CCR7
- increases this to go to B cell zone
CXCR4
- downregulates this to go to T cell zone

Question 16

What do CCR7 and CXCR4 do to both T cells and B cells?

Answer 16

move them to the germinal center region (space between the B and T cell zones)

Question 17

What are the steps of antigen presentation by B cells to helper T cells?

Answer 17

• B cell recognizes protein antigen
• receptor-mediated endocytosis of antigen
• antigen processing and presentation via class II MHC complex
• T cell recognition of antigen on B cell

Question 18

What is required for T cells to activate a B cell besides the MHC complex?

Answer 18

CD40 on B cell
CD40L on T helper cell

Question 19

Where do B cells proliferate?

Answer 19

germinal center of lymph node

Question 20

When do B cells leave the germinal center of lymph node?

Answer 20

leave if they are high-affinity antibody-secreting cells and memory B cells

Question 21

What allows for B cells to be activated to anything other than IgM?

Answer 21

CD40L
cytokines
IL-4 (IgE)
etc.

Question 22

What is the effector function of IgM?

Answer 22

complement activation

Question 23

What is the effector function of IgG?

Answer 23

• Fc receptor-dependent phagocyte responses
• complement activation
• neonatal immunity

Question 24

What is the effector function of IgE?

Answer 24

• immunity against helminths
• mast cell degranulation

Question 25

What is the effector function of IgA?

Answer 25

• mucosal immunity

Question 26

What is the mechanism of immunoglobulin heavy-chain isotype switching?

Answer 26

• induction of AID (activation-induced deaminase) which alters nucleotide to they can be cleaved
• switch recombination: Previously formed VDJ exon recombines
  to become adjacent to a different
  constant region gene
• transcription, RNA splicing, and translation

Question 27

What is the point of activation-induced deaminase?

Answer 27

alters nucleotides so they can be cleaved by other enzymes, allowing S regions to be brought together (isotype switching)

Question 28

What is switch recombination when isotype switching?

Answer 28

Previously formed VDJ exon recombines to become adjacent to a different constant region gene

Question 29

Repeated exposure to a protein antigen drives creation of _______ affinity antibodies

Answer 29

higher

Question 30

Somatic mutations in Ig V genes leads to…

Answer 30

selection of high-affinity B cells

Question 31

What do follicular dendritic cells do in forming high-affinity B cells?

Answer 31

present antigen via antibodies bound to Fc receptors or complement receptors instead of MHC molecules Antigens are never internalized by FDCs

Question 32

What are the characteristics of T cell-dependent antigens?

Answer 32

chemical nature: proteins
isotype switching: yes
affinity: yes
life span: long-lived
secondary response: yes

Question 33

What are the characteristics of T cell-independent antigens?

Answer 33

chemical nature: polymeric antigens (polysaccharides, glycolipids, and nucleic acids)

isotype switching: low level switching

affinity: little or no

life span: short-lived

secondary response: only with some polysaccharide antigens

Question 34

Humoral response terminated once sufficient quantities of IgG are produced to result in…

Answer 34

inhibition of B cell response

Question 35

If a antigen-antibody complex binds to 2 different Fc receptors then it does what?

Answer 35

blocks B cell receptor signaling
- antibody feedback