B cell immunity Flashcards

1
Q

B cell immunity helps destroy __________ pathogens.

A

Extracellular

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2
Q

_________ bind to microbial agents and help in their destructions.

A

Antibodies

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3
Q

This cell type produces antibodies.

A

B cells

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4
Q

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

A

Antibodies

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5
Q

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

A

Protein antigens and non-protein antigens

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6
Q

TCR can only bind to what type of antigen?

A

Protein antigen

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7
Q

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

A

Effector cells and memory cells

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8
Q

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

A

While circulating through the lymphoid tissues.

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9
Q

What is the function of plasma cells?

A

Secrete antibodies

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10
Q

What is a difficulty when studying B cells?

A

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

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11
Q

What is the BCR?

A

membrane bound Ig molecules

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12
Q

What are antibodies?

A

Soluble Ig molecules

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13
Q

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

A

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

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14
Q

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

A

Secondary lymphoid tissues

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

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15
Q

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

A

Binding to its specific antigen and a Tfh cell

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16
Q

Antibodies return where?

What do they help fight against?

A

Return to infected tissue.

Help fight EXTRAcellular pathogens.

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17
Q

How many Ig isotypes are there? What are they?

A

5

IgA, IgM, IgD, IgG, IgE

18
Q

What is the differentiating factor between Ig classes?

A

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

19
Q

Where do all immune cells arise from?

A

Bone marrow

20
Q

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

A

(Mature) naive B cells

21
Q

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

A

Co-express IgM and IgD

22
Q

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

A

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

23
Q

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

A

Naive B cell

24
Q

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

A

Protein antigens

25
Q

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

A

Tfh cell

26
Q

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

A
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.
27
Q

What happens after B and Tfh cell binding?

A

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

28
Q

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

A

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

29
Q

What is class switching?

A

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

30
Q

How is class switching accomplished (Genetically)?

A

Re-arrangement of the heavy chain constant region genes.

31
Q

Does class switching affect antigen binding?

A

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

32
Q

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

A

Tfh cytokines

33
Q

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

A

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)

34
Q

What antibody type is always secreted first?

A

IgM

35
Q

Where does class switching occur?

A

Germinal center

36
Q

Why is class switching even necessary?

A

IgM doesnt enter the tissues

37
Q

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

A

Reside in the bone marrow

Constitutively secrete antibody

38
Q

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

A

Months to years

39
Q

How long do short-lived plasma cells live for?

A

5-10 days

40
Q

Where is adaptive immunity always initiated?

A

SLTs

41
Q

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

A

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.
42
Q

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

A

IgM - short-lived plasma cell