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MIIM30002 > Lecture 22: Cellular Interactions and Trafficking - B cells > Flashcards

Lecture 22: Cellular Interactions and Trafficking - B cells Flashcards

1
Q

Following development, what can B cells mature into?

A

B-1 B cells and B-2 B cells which can differentiate into follicular or marginal zone B-2 B cells

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2
Q

What are characteristics of B-1 B cells?

A

progenitors distinct from B-2 B cells
mostly recognise capsular polysaccharide antigens
able to produce IgM without T cell help

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3
Q

What are the different types of B-2 B cells?

A

marginal zone, follicular and memory B cells

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4
Q

Why is there continual competition for entry of B-2 B cells?

A

due to limited number of follicles which favour established B cells

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5
Q

Where are marginal zone B cells found?

A

in the marginal zones of the white pulp

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6
Q

What is the role of marginal zone B cells?

A

poised to make rapid responses to blood-borne antigens

relatively broad specificity

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7
Q

What responses do marginal zone B cells produce?

A

typically T cell independent responses and does not generate memory

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8
Q

What are follicular B cells and what do they express?

A

form the majority of B cells and are involved in the co-expression of IgM and IgD

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9
Q

What are follicular B cells capable of? What is their activation threshold like?

A

recirculating through lymphoid tissues

higher activation threshold for proliferation and differentiation

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10
Q

What is the role of memory B cells?

A

rapid response to re-encounters

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11
Q

Why are memory B cells usually less differentiated?

A

so they have the ability to refine Ab affinity

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12
Q

What is the role of B cell responses?

A

antibody secretion to protect from extracellular pathogens and toxins

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13
Q

What are antibodies involved in?

A

neutralisation, opsonisation and complement activation

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14
Q

What do B cell responses require in order to be activated?

A

require activation of naive B cells

require multiple signals

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15
Q

When do T cell independent responses occur?

A

typically with highly repetitive molecules such as polysaccharides of bacterial cell walls

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16
Q

What do T cell independent responses involve?

A

activation of B cells without T cell help

activated by the cross linking of BCRs

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17
Q

What are T cell independent responses normally limited to?

A

usually limited to IgM but cytokines may enhance response

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18
Q

What is required for the activation of T cell dependent responses?

A

require multiple signals to induce efficient responses

dependent on CD40/CD40L interaction between B cells and Tfh

19
Q

What is important in maintenance of self-tolerance?

A

both CD4 T cells and B cells have to to be activated during a T cell response

20
Q

How are antigens detected by B cells?

A

native antigen can passively drain through lymphatics

key roles for other cell types in active presentation e.g. subcapsular macrophages and follicular dendritic cells

21
Q

Where are subcapsular macrophages found?

A

in subcapsular sinus of LNs and marginal sinus of the spleen

22
Q

What is the role of subscapular macrophages?

A

able to take up antigen but does not degrade them

decorates the surface with antigen

23
Q

What are follicular dendritic cells and where are they found?

A

not dendritic cells but stromal cells which are found embedded throughout the follicles

24
Q

What type of cell are follicular dendritic cells?

A

non-phagocytic cell of non-hematopoietic origin

25
Q

What is the role of follicular dendritic cells?

A

presents antigen to B cells

26
Q

What do most humoral responses require?

A

require B cells to interact with T cells

27
Q

Why do B cells reside in follicles and what happens following activation?

A

due to expression of CXCR5 which is attracted to CXCL13

B cells upregulate CCR7 to move towards the paracortex

28
Q

What are T cells activated by?

A

DCs in the paracortex

29
Q

What happens following activation of T cells? What are fully differentiated Tfh cells able to do?

A

upregulate CXCR5 and moves towards the high concentration of CXCL13
able to move into the follicle and sustain responses there

30
Q

How does the first interaction between T and B cells promote Tfh differentiation?

A

activates ICOS signalling on T cells which induces transcription of Bcl-6 and c-Maf and allows for sustained contacts between B and Tfh cells

31
Q

What happens during sustained contact between B and Tfh cells?

A

B cell responses continue and form germinal centres

32
Q

What do germinal centres develop from and what are they composed of?

A

develop from primary foci and are composed of mainly rapidly proliferating B cells

33
Q

What can germinal centres be divided into?

A

the mantle zone, dark zone and light zone

34
Q

What is the role of germinal centres?

A

site for class switching and somatic hypermutation

35
Q

What do dark zones of germinal centres contain?

A

centroblasts

high proliferation

36
Q

What do light zones of germinal centres contain?

A

centrocytes

lower proliferation but has higher levels of surface Ig

37
Q

What are plasmablasts and where are they found?

A

short lived antibody secreting cells which are found in primary foci shortly after B and T cell interaction

38
Q

What is the role of plasma cells?

A

can migrate into the bone marrow and become long-lived antibody secreting cells

39
Q

What is the role of memory B cells?

A

long lived cells capable of rapid responses following reencounter

40
Q

What do V(D)J rearrangements during B cell development provide?

A

diversity and generates closely related clones that are independent of recombination

41
Q

What is the role of somatic hypermutation?

A

allows B cells to mutate the genes that they use to produce antibodies
this enables B cells to produce antibodies that are better able to bind to bacteria, viruses and other infections

42
Q

What is antibody specificity defined by?

A

the variable region

43
Q

What is the role of the constant region?

A

dictates the effector function of an antibody

44
Q

What does T cell help with CD40L allow B cells to do?

A

to use different constant regions of the heavy chain and this generally increases the effectiveness following class switching

MIIM30002 (25 decks)

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