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Host Defense Exam 2 > B Cell Immunity > Flashcards

B Cell Immunity Flashcards

1
Q

What is unique about the properties of B1 and MZ cells?

A
  • behave innate-like

- first line of defense

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2
Q

Describe the following characteristics related to B1 cells:

  • time of production
  • diversity
  • mode of renewal
  • antigen
  • T cell involvement
A
  • produced in the fetus
  • not so diverse b/c no N regions
  • self-renewing
  • yes to CHO, sometimes to protein
  • no T cells
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3
Q

Describe the following characteristics related to B2 (conventional) cells:

  • time of production
  • diversity
  • mode of renewal
  • antigen
  • T cell involvement
A
  • produced after birth
  • very diverse
  • regenerated from the bone marrow
  • mostly protein, sometimes CHO
  • requires T cell (adaptive immunity)
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4
Q

Describe the following characteristics related to MZ B cells:

  • time of production
  • diversity
  • mode of renewal
  • antigen
  • T cell involvement
A
  • produced after birth
  • somewhat diverse (has N regions, but limited Vs)
  • long-lived (no renewal)
  • both CHO and protein
  • sometimes interacts with T cells
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5
Q

What has increased immunogenicity:

  • size
  • dose
  • composition
  • form
  • adjuvants
A
  • large
  • intermediate dose
  • complex composition
  • insoluble
  • slow release adjuvants, bacterial adjuvants
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6
Q

Why are intermediate doses given for an immune response?

A
  • low dose might not generate a response

- high dose can cause tolerance

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7
Q

Why do insoluble antigens have more immunogenicity?

A

b/c when solubilized it is harder for phagocytic cells to take them up

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8
Q

Define adjuvant.

A

molecule or peptide used to enhance the immune response to a particular antigen

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9
Q

What is the most common adjuvant?

A
  • alum (aluminum hydroxide)
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10
Q

How does alum work?

A
  • alum is insoluble and when combined with a soluble antigen => precipitated aggregate => easier to uptake
  • instigates inflammasome reaction
  • delayed antigen release
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11
Q

What signals are required for B cell activation?

A
  1. TCR:MHC:CD4

2. CD40L:CD40

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12
Q

Describe thymus-dependent antigen reactions.

A
  • mostly peptide antigens
    1. TCR:MHC:peptide
    2. T cell secretes stimulatory cytokines: IL-4, IL-5, IL-6
    3. T cell expresses CD40L => CD40
    4. B cell activated to proliferate
    5. B cell differentiates into a memory cell or a plasma cell
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13
Q

How can you immunize an infant, who cannot produce T-independent immune responses, against a polysaccharide antigen?

A

NOTE: T cells and B cells must recognize the same antigen
1. attach a protein (tetanus toxoid) to the polysaccharide (H. influenza) structure
2. polysaccharide antigen will bind to its specific B cell
3. B cell processes the antigen
4. antigen presentation only occurs with the peptide fragment because polysaccharides cannot bind to the MHC antigen-binding cleft
5. T cell recognizes MHC and peptide => gives B cell the okay to proliferate and make memory/plasma cells
6. B cell produces the SAME antibody it had on its surface = the one against the polysaccharide structure
Thus, the antibodies produced are against the polysaccharide even though the T cell recognized only the peptide

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14
Q

Differentiate primary and secondary antibody response.

A

Primary

  • slow
  • IgM

Secondary

  • rapid
  • IgG
  • more antibody (higher titer)
  • increased affinity
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15
Q

How and when does an isotype switch occur?

A
  • How: rearrange the remaining heavy chain constant region genes by looping out DNA
  • When: T-dependent responses, regulated by T-cell cytokines
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16
Q

What are some examples of T cell cytokines that induce isotype switch?

A
  • IL4 causes switch from IgG to IgE
  • TGFB causes switch to IgA
  • IFNg causes switch to IgG3
17
Q

Recall the mechanism for isotype switching.

A
  • enzyme AID (activation-induced cytidine deaminase)
    1. recognizes switch regions in front of the remaining C genes of the heavy chain
    2. loops out the DNA in between => excised => ligated
    3. you are left with a new C region on the DNA
    NOTE: only possible if there are C regions left on the 3’ end of theW DNA after the original VDJ-C rearrangement
18
Q

What activities occur in the germinal centers?

A
  • B cell proliferation
  • isotype switch
  • somatic hypermutation
  • development of memory or plasmablast cells
  • forms during immune response*
19
Q

What are the possible results of somatic hypermutation?

A
  1. creation of a high affinity surface Ig => memory or plasma cell
  2. creation of a low affinity surface Ig or a totally different specific affinity Ig => apoptosis b/c no activation from Thelper cells in the GC
20
Q

Define somatic hypermutation.

A

occurs after B cell is activated to proliferate

  • purpose: generate a high specificity antibody against the antigen
  • mutations occur in the V regions
21
Q

Describe the mechanism of somatic mutation.

A
  1. activated B cell undergoes somatic hypermutation in the GC via AID enzyme
  2. follicular dendritic cell present an antigen-antibody complex to test the affinity of the new antibody
  3. if the new antibody is specific enough, the T cell will be activated again and stimulate the B cell to become a plasma or memory cell
  4. if the new antibody is not specific => apoptosis
22
Q

What enzyme is used in hypermutation?

A

AID

23
Q

What happens in patients with AID deficiency?

A

can only make IgM

no somatic diversity

24
Q

What happens to hypermutation with time?

A

as time goes on, more and more mutations occur, creating more specificity

25
Q

How do T Helper cells enhance antibody production?

A
  1. Th + APC (macrophage, dendritic cell) => activated T cell (via TCR:MHCII)
  2. activated T-cell + Ag-B cell => activated B cell => plasma or memory
26
Q

Describe the characteristics of a T-independent response.

A
  • usually for polysaccharide antigens
  • forms IgM antibody mostly
  • no somatic hypermutation
  • rapid response to bacteria and bacteria-associated polysaccharides
  • no memory cells usually
  • 2nd signal is provided by antigen itself (no need for CD40:CD40L

Host Defense Exam 2 (11 decks)

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