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MIMM 214 > B Cells 2 > Flashcards

B Cells 2 Flashcards

1
Q

do the 2 signals of B cell activation occur at the same time or sequentially? why?

A

they occur sequentially

because p:BCR allows internalization of peptide for presentation of MHCII which can then interact with TCR

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2
Q

where does B cell activation, differentiation, and proliferation occur?

A

in different parts of the lymph node

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3
Q

what is the subcapsular sinus?

A

casing of the lymph node

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4
Q

what occurs in the subcapsular sinus?

A

SCS macrophages are located here and encounter Ag

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5
Q

what occurs in the T cell zone?

A

T cells reside here once they enter thru HEV and get activated by interacting with DCs/APCs

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6
Q

what occurs in the B cell zone?

A

B cells encounter Ag and undergo proliferation and differentiation

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7
Q

why is the B cell zone closer to the subcapsular sinus than the T cell zone?

A

B cells have to be in close contact to SCS macrophages to be activated so the B cell zone must be closer to the subcapsular sinus

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8
Q

what is the T-B border? what occurs here?

A

Border btwn T and B cell zones

this is where B cells receive signal 2 via T cells

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9
Q

where are follicles and the germinal centers located?

A

B cell zone

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10
Q

in general, what occurs at follicles?

A

B cells develop and get activated

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11
Q

in general, what occurs at germinal centers?

A

site of INTENSE B cell proliferation and differentiation

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12
Q

describe 6 steps of B cell activation

A
  1. B cell encounters free-floating Ag, Ag on SCS macrophages, or Ag on follicular DCs in the B CELL ZONE
  2. BCR:Ag endocytosed and processed
  3. increased MHC II expression
  4. increased chemokine receptor expression
  5. B cell targeted to T-B border by chemokines
  6. B cell receives signal 2 at T-B border and becomes activated
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13
Q

when does MHC II expression increase? why?

A

once BCR:Ag is endocytosed and processed, MHC II expression increases

lets you present more peptides to increase the chance of meeting TCR

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14
Q

what type of T cell is responsible for activating B cells?

A

Tfh

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15
Q

on which cells is there an increased expression of chemokine receptors? why?

A

T and B cells –> so they can reach the T-B border

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16
Q

what are the 2 choices of an activated B cell?

A
  1. form PRIMARY FOCUS in subcapsular region
  2. migrate to follicle to form GERMINAL CENTER
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17
Q

describe the 3 steps of forming a primary focus

A
  1. SIGNAL 1 –> in B cell zone
  2. SIGNAL 2 –> at T-B border
  3. B cells become plasmablasts and form primary focus near the subcapsular region
18
Q

what type of cell do B cells become when they form the primary focus?

A

plasmablasts

19
Q

describe the steps of forming a germinal center

A
  1. SIGNAL 1 –> in B cell zone
  2. SIGNAL 2 –> at T-B border
  3. go to follicle to form Germinal Center (GC reaction), where B cells become plasma cells
20
Q

what are the 2 ways that plasma cells are formed?

A
  1. B cells become plasmablasts then become plasma cells
  2. directly become plasma cells from B cells
21
Q

what are plasmablasts? (4 things)

A
  1. differentiated B cells that have begun to secrete IgM antibodies (early Ab production)
  2. but still have cell surface BCRs
  3. can still proliferate
  4. arise from primary focus
22
Q

describe antibodies on naive B cells

A

naive B cells have cell surface IgM and DO NOT secrete antibody

23
Q

what are plasma cells?(4 things)

A
  1. differentiated B cells that rapidly secrete large numbers of diverse Ab with high affinities
  2. little to no cell surface immunoglobulin
  3. cannot proliferate
  4. arise from germinal center reaction
24
Q

what are the 2 main outcomes of the primary focus?

A
  1. plasmablast
  2. IgM+ memory B cells
25
Q

what do plasmablasts produce vs what do IgM+ memory B cells produce?

A

plasmablasts –> early antibody production (mainly IgM)

IgM+ memory B cells –> only IgM production

26
Q

where does the primary primary focus form? (3 places)

A
  1. near subcapsular zone
  2. in interfollicular regions (surrounding follicles)
  3. in medullary cords
27
Q

what happens to B cells in the primary focus?

A

undergo proliferation and differentiation into plasmablasts

28
Q

when do primary foci occur?

A

5 days after primary infection (i.e. 5 days after post-Ag presentation)

29
Q

what are the 2 fates of plasmablasts?

A
  1. die by apoptosis within 5-10 days after secreting IgM
  2. migrate to bone marrow to become plasma cells to continue Ab production
30
Q

what is another name for the germinal center?

A

Secondary Lymphoid follicle

31
Q

what are the 2 main outcomes of the germinal center/Secondary Lymphoid follicle?

A
  1. plasma cell
  2. memory B cell
32
Q

what do plasma cells secrete?

A

large quantities of antibodies

33
Q

why are memory B cells important?

A

important for memory response –> maintain capacity to produce higher affinity antibodies for a secondary antigen exposure

34
Q

describe what happens in the germinal center/Secondary Lymphoid follicle

A
  1. B cells receive signals 1 and 2 AGAIN (2nd time)
  2. B cells undergo differentiation to make more antibodies that are more effective with higher affinity
  3. size peaks at 7-12 days after antigen stimulation
35
Q

what allows B cells to receive signals 1 and 2 again? why do they receive them again?

A

germinal center has many cell types, including T cells so B cells can be further activated

36
Q

what are the 3 mechanisms that B cells produce more antibodies that are more effective with higher affinity?

A
  1. somatic hypermutation
  2. affinity maturation
  3. class switching
37
Q

where do plasmablasts secrete their antibodies?

A

mainly in lymph node

38
Q

where do plasma cells secrete their antibodies?

A

can either stay in medulla of lymph node or travel to bone marrow and reside there

39
Q

are antibodies from plasmablasts or plasma cells produced first?

A

plasmablasts

40
Q

are antibodies from plasma cells IgM?

A

no –> they switch classes

41
Q

what are the 3 general functions of antibodies?

A
  1. neutralization
  2. opsonization
  3. complement activation

MIMM 214 (33 decks)

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