B cell immunity

Question 1

B cell immunity helps destroy __________ pathogens.

Answer 1

Extracellular

Question 2

_________ bind to microbial agents and help in their destructions.

Answer 2

Antibodies

Question 3

This cell type produces antibodies.

Answer 3

B cells

Question 4

________ go back to infected tissues, bind to pathogens and coat their surface.

Answer 4

Antibodies

Question 5

BCR can bind directly to what antigen type(s)?

Answer 5

Protein antigens and non-protein antigens

Question 6

TCR can only bind to what type of antigen?

Answer 6

Protein antigen

Question 7

Primary response (in B cells) produces these cell types.

Answer 7

Effector cells and memory cells

Question 8

Where does the naive B cell encounter its specific epitopal region?

Answer 8

While circulating through the lymphoid tissues.

Question 9

What is the function of plasma cells?

Answer 9

Secrete antibodies

Question 10

What is a difficulty when studying B cells?

Answer 10

Naive B cells and memory B cells look identical (can only differentiate with surface markers)

Question 11

What is the BCR?

Answer 11

membrane bound Ig molecules

Question 12

What are antibodies?

Answer 12

Soluble Ig molecules

Question 13

Can more than one B cell bind to a specific antigen?

Answer 13

Yes, multiple B cells can bind to different epitopes on the same antigen.

Question 14

B cell circulates through ________ ________ ________. If a B cell doesn not bind its antigen, what happens?

Answer 14

Secondary lymphoid tissues

it remains inactive and re-circulates. (Ultimately will die of apoptosis if it doesn’t meet its antigen)

Question 15

What are the necessary requirements for a B cell to undergo clonal expansion?

Answer 15

Binding to its specific antigen and a Tfh cell

Question 16

Antibodies return where?

What do they help fight against?

Answer 16

Return to infected tissue.

Help fight EXTRAcellular pathogens.

Question 17

How many Ig isotypes are there? What are they?

Answer 17

5

IgA, IgM, IgD, IgG, IgE

Question 18

What is the differentiating factor between Ig classes?

Answer 18

NOT the variable region, but rather differences in the heavy chain constant region.

Question 19

Where do all immune cells arise from?

Answer 19

Bone marrow

Question 20

B cells, after development, arrive in the blood under what form?

Answer 20

(Mature) naive B cells

Question 21

What Ig receptor(s) do naive B cells express?

Answer 21

Co-express IgM and IgD

Question 22

Do the co-expressed IgD and IgM have different specificities?

Answer 22

No, only differences in heavy chain constant region. Bind to the same epitope (or specific for more accurately)

Question 23

Which B cell type is the one that circulates through the SLT and responds to pathogens it has specificity for?

Answer 23

Naive B cell

Question 24

The most common B cell response is against what type of antigens?

Answer 24

Protein antigens

Question 25

B cell response to a protein antigen requires the help of what cell type?

Answer 25

Tfh cell

Question 26

Describe the events starting in the SLT, to binding to a Tfh cell.

Answer 26

Naive B cell circulates in the SLT and binds to protein antigen.
B cell takes up pathogen by endocytosis - lysosome fuses with endosome.
B cell presents peptide fragments on MHC class 2 molecule to a Tfh cell with the same specificity.

Question 27

What happens after B and Tfh cell binding?

Answer 27

Both the B and T cell get activated, leading to clonal expansion for both.
This binding causes release of Tfh cell cytokines.

Question 28

What are the three fates of a naive B cell undergoing clonal expansion?

Answer 28

1 - Memory B cells - co-express IgM and IgD
2 - Short-lived plasma cells - secrete IgM antibodies
3 - Tfh cells and other B daughter cells form a germinal center, where the GC B cells undergo class switching

Question 29

What is class switching?

Answer 29

GC B cell switches its Ig class (from IgD/M –> IgG/A/E)

Question 30

How is class switching accomplished (Genetically)?

Answer 30

Re-arrangement of the heavy chain constant region genes.

Question 31

Does class switching affect antigen binding?

Answer 31

No, variable region is unaffected - so antigen specificity remains the same.

Question 32

What is the Ig class change (during class switching) determined by?

Answer 32

Tfh cytokines

Question 33

What are the two possible fates of a GC B cell?

Answer 33

Either becomes a long-lived plasma cell (secretes antibody type it class switched to) or becomes a memory B cell (Expresses Ig molecule as BCR it class switched to)

Question 34

What antibody type is always secreted first?

Answer 34

IgM

Question 35

Where does class switching occur?

Answer 35

Germinal center

Question 36

Why is class switching even necessary?

Answer 36

IgM doesnt enter the tissues

Question 37

Where do long-lived plasma cells reside? What do they do?

Answer 37

Reside in the bone marrow

Constitutively secrete antibody

Question 38

How long do long-lived plasma cells reside in the bone marrow?

Answer 38

Months to years

Question 39

How long do short-lived plasma cells live for?

Answer 39

5-10 days

Question 40

Where is adaptive immunity always initiated?

Answer 40

SLTs

Question 41

Describe, how Tfh and B cells get activated, and their outcomes.

Answer 41

Dendritic cell phagocytoses extracellular bacterium. Moves to the secondary lymphoid tissues and presents peptide on MHC class 2 molecule to naive Th cell, which becomes a Tfh cell.

Next, pathogen in SLTs, taken up by naive B cell by endocytosis, presents peptide on MHC2 molecule and binds to Tfh cell.

Naive B cell and Tfh cell undergo clonal expansion. B cell can become a memory cell, plasma cell or a GC B cell.
Within the germinal center, Tfh cell releases cytokines, which dictate to what class the B cell can switch. 
The GC B cell can either become a memory cell or long-lived plasma cell.

Question 42

In the primary response, which antibody is secreted first? By which cell?

Answer 42

IgM - short-lived plasma cell