MI 03c: B cell Activation Flashcards by Nuna H

Naive B cells, like T cells, migrate from circulation to (X) via (Y). The difference, though, is (Z).

X = peripheral lymphoid organs
Y = chemokines
Z = chemokine receptor CXCR5 (not CCR7)

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Chemokine receptor (X) on naive B cells directs them to (Y) part, the B zone, of peripheral lymph organs.

X = CXCR5;
Y = follicles

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In the B cell zone, naive B cells are presented with (X)-coated (Y) via (Z) cells.

X = C3b and C3d complement
Y = microbial antigens
Z = follicular DCs

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Activated B cell will proliferate and differentiate into (X). (X) cells (do/don’t) further (differentiate/divide).

X = plasma cell;

Don’t divide/differentiate further

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Plasma cells are dedicated to which function?

Secretion of their Ab product

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BCR binding avidity is increased by interaction of (X) co-receptor on B cell, which binds to (Y) complement fragment.

X = CR2
Y = C3d

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T/F: B cell co-receptor has signaling domain.

False

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T/F: BCR has signaling domain.

False

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(X) B cell co-receptor, which is associated with (Y), has intra-cytoplasmic signaling domain.

X = CD19
Y = CR2 (co-receptor)

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The (X) is associated with (1/2/3) (Y) that contain signaling domains. This forms the BCR complex.

X = BCR;
2;
Y = heterodimers

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B cell activation: as an alternative to co-receptor engagement, avidity/signaling may be increased by binding of (X) to (Y).

X = TLRs (on B cell)
Y = PAMP (on microbial particle)

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B cell activation: Engagement of BCR and either (X) or (Y) leads to activation of transcription factors in B cell.

X = CR2
Y = TLRs

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Depending on (X), B cell can proliferate/differentiate through one of which two pathways?

X = nature of antigen

T independent
T-dependent

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T (dependent/independent) antigens are typically (X) and have no protein component.

Independent

X = capsular polysaccharides and lipids (with repeating identical units)

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CHO attached to protein activates B cell. What’s the subsequent fate of this T-(dependent/independent) antigen?

T-dependent;

Endocytosis
Processing and presentation on MHC Class II molecules

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When B cell encounters T-(dependent/independent) antigen, it needs to express (X) receptor to assist in B cell migration from (Y) to (Z).

T-dependent;
X = CCR7
Y = follicle
Z = T cell zone

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A T-dependent antigen is presented by B cell to (X), which has begun its differentiation to (Y).

X = CD4 T cell
Y = Th1, Th2, or Th17 helper cell

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T-dependent antigen pathway: (T/B) cell activates (T/B) cell to proliferate.

Both; both (mutual activation/proliferation)

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T-dependent antigen pathway: (X) and (Y) induces some of the B cells to upregulate (Z) receptor and return to the follicle (with/without) the T cell.

X = tight T cell contact
Y = cytokines produced by T cell
Z = CXCR5

With

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T-(dependent/independent) pathway: B cell, returns to follicle with T, specifically (X), cell. This generates which part of the follicle?

T-dependent;
X = Tfh
Germinal center

Germinal center of follicle contains proliferating, differentiating (X) cells that continue to receive stimulation from (Y).

X = B
Y = Tfh cells and FDC-displayed antigen

What are secondary follicles?

Follicles containing germinal center

B cells that don’t return to follicle have which fate?

Differentiate into short-lived IgM-secreting plasma cells

List the three processes that the (X) cell undergoes in germinal center.

X = B

Ig class switching
Somatic hypermutation/affinity maturation
Generation of memory B cells

In germinal center, T cell express (X) ligand and secrete cytokines, which engage (X) and cytokine receptors on B cell it's in contact with. This effects the B cell in which way?

X = CD40 1. Further proliferation/differentiation 2. Expresses enzyme (AID)

The enzyme AID is expressed by (X) cell in (Y) location and is important for (Z).

``` X = B Y = germinal center Z = Ig class switching and somatic hypermutation ```

Different Ig isotypes are different in which functions?

Mediate different effector functions (eradicate different types of microbes)

T/F: Portion of IgH DNA is deleted during Ig switching.

True

Aside from Tfh cytokines, (X) cytokine secretion from (Y) cell required for Ig switching to IgG1 and IgG3.

``` X = IFN-gamma Y = Th1 ```

Aside from Tfh cytokines, (X) cytokine secretion from (Y) cell required for Ig switching to IgE.

``` X = IL-4 Y = Th2 ```

Aside from Tfh cytokines, (X) cytokine secretion from (Y) cell required for Ig switching to IgA.

``` X = IL-5 Y = Th2 ```

Hyper-IgM syndrome is (X) disease caused by (Y).

``` X = immunodeficiency Y = defective expression of CD40L on Th cells ```

Hyper-IgM syndrome prevents (X) process from occuring, resulting in (low/high) levels of (Y) in blood.

X = Ig switching High Y = IgM

T/F: Hyper-IgM syndrome leads to reduced elimination of microbes.

True

Somatic hypermutation of (X) cells is the introduction of (Y) in (Z). What does this do?

``` X = B Y = many point mutations Z = variable region genes of expressed Ab ``` Affinity changes

Following somatic hypermutation, the selected (X) cells give rise to (Y) cells. These secrete Ab that differ in which characteristic?

``` X = B Y = plasma ``` Higher affinity

Majority of activated proliferating follicular B cells have which fate?

Terminal differentiation to long-lived plasma cells

Some follicular B cells differentiate into long-lived memory B cells. Which contact/signals aid in this differentiation?

T cell contact and cytokines

Memory B cells secrete which Ab?

They don't secrete Ab (stays on surface as BCR)

T/F: Memory B cell Ab is class-switched and high affinity.

True

Memory B cells are present in (smaller/larger/equal) numbers and are activated (slower/quicker) than naive B cells upon repeat encounter.

Larger; quicker

T-independent antigens are typically presented on class (I/II) MHC molecules.

Neither! NO peptides in antigen

T-independent pathway: (few/many) interactions of (X) molecules with repeating epitopes on antigen leads to (X) crosslinking, activation, proliferation, and terminal differentiation to (Y).

Many; X = BCR Y = short-lived IgM-secreting plasma cells

A subset of (X) cells in marginal zone of spleen are self-renewing and express (Y) specific for (Z) antigens.

``` X = B Y = BCR Z = capsular polysaccharides (T-independent) ```

Marginal zone of spleen is major source of (X) against microbial capsular polysaccharides.

X = IgM

Why is humoral immunity, provided by (X), against capsular microbes (i.e. bacteria) so important?

X = IgM (produced by plasma cells in spleen) Capsule protects bacteria from phagocytosis via innate immune system

Which Ig isotypes are long-lived (years)? Where is "home" for each (X) cell that expresses them?

X = plasma IgA (mucosa) IgG (bone marrow) IgE (submucosa/skin)

B cell markers are (X) specific to them. List the ones unique to B cells.

X = surface proteins Ig (BCR), CD19 and CD20