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Imunology > B Lymphocytes > Flashcards

B Lymphocytes Flashcards

1
Q

Where are B cells developed in mammals?

A

bone marrow

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2
Q

Where are B cells developed in birds?

A

bursa of fabricius

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3
Q

What are the stages of B cell development?

A
  • Pro-B cell stage
  • Pre-B cell stage
  • Immature B cell stage
  • T1 stage
    -T2 stage
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4
Q

What are the stages of the Pro-B cell stage?

A

early and late

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5
Q

What happens in the early Pro-B cell stage?

A
  • D to J heavy chain recombination
  • initiation of V to DJ heavy chain recombination
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6
Q

What happens in the late Pro-B cell stage?

A
  • complete V to DJ heavy chain recombination
  • commitment to B cell lineage
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7
Q

What happens in the Pre-B cell stage?

A
  • express a precursor BCR-m heavy chain
  • proliferation occurs
  • daughter cells undergo light chain recombination
  • precursor B cell receptor (BCR) is no longer expressed
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8
Q

What happens in the Immature B cell stage?

A
  • express BCR that is membrane-bound IgM (mIgM)
  • cells undergo negative selection
  • at end of immature B cell stage, these cells leave bone marrow/bursa, travel through bloodstream, enter spleen as T1 B cells (transitional)
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9
Q

What happens during negative selection?

A
  • select against cells that bind self-antigen
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10
Q

What happens to cells that recognize self antigen?

A
  • apoptosis or undergo receptor editing
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11
Q

What is receptor editing?

A

new V and J genes are selected for light chain of BCR

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12
Q

What happens during T1 stage?

A
  • cells undergo negative selection
  • cells begin to express membrane bound BCR IgD in addition to membrane bound BCR IgM
  • cells express receptor for B cell activating factor (BAFF)
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13
Q

What happens during T2 stage?

A
  • cells receive BAFF signaling
  • cells receive survival signals through mIgM and mIgD
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14
Q

What happens after the T2 stage?

A

mature naive B cells enter circulation

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15
Q

What are the two types of B cell activation?

A
  • T helper dependent activation
  • T independent activation
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16
Q

What is the goal of B lymphocyte activation?

A

get plasma cells that secrete antibodies

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17
Q

What happens when B cells enter subcapsular sinus?

A

migrate to follicle in the lymph node

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18
Q

What do B cells encounter in the follicle?

A

the antigen they are specific for

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19
Q

Can B cells recognize free antigens?

A

yes

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20
Q

Can T cells recognize free antigens?

A

no

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21
Q

What kinds of antigens can B cells bind in the follicle?

A
  • free floating antigen
  • antigen-bound complement
  • antigen bound to follicular dendritic cells
  • antigen bound to subcapsular sinus macrophages
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22
Q

How are microclusters formed?

A
  • when BCR binds antigen, changes in B cell membrane occur, resulting in expansion of membrane
  • membrane then contracts back, leaving microclusters of BCRs on the membrane
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23
Q

What needs to happen if the antigen is bound to another cell?

A

need it to break away

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24
Q

How can an antigen be broken away from another cell?

A

2 ways
- lysosomes within the B cell can migrate to the cell membrane and release compounds that cleave the connection between the antigen and other cell
- cell membrane with polymerized actin can push against the other cell, and the force causes the other antigen to break off

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25
Q

What happens after BCR binds to antigen (and broken off of cell if needed)?

A
  • B cell internalized BCR and antigen
  • antigen is internalized and processed and presented on MHC-II
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26
Q

What happens after antigen presented on MHC-II?

A

the B cells move to T cell zone of lymph node

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27
Q

What does the B cell encounter in the T cell zone?

A

differentiated helper T cells

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28
Q

How do the B cells interact with T cells in T cell zone?

A
  • MHC-II antigen complex on B cell binds to TCR complex on T cell
  • B cells express CD80 and CD86 that bind to CD28 on T cell
  • CD40 on B cell binds to CD40L on T cell
  • TH cell secretes cytokines (IL 2 and IL 4)
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29
Q

What do the ways the B cell interacts with T cells in T cell zone result in?

A

all of these signals cause B cell to proliferate

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30
Q

What happens as the B cell proliferates after signals from T cell zone?

A

it loses expression of membrane bound IgD and only expresses membrane bound IgM

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31
Q

Where does T independent activation occur?

A

all in the follicle

32
Q

How is T independent activation similar to T helper dependent activation?

A
  • still get BCR binding to antigen
  • B cell proliferates and loses expression of membrane bound IgD
33
Q

How is T independent activation different than T helper dependent?

A

get crosslinking with PRR

34
Q

What is crosslinking with PRR?

A

antigen bound to PRR and BCR, so get signaling through both
- (2 receptors bound to same thing)

35
Q

What are problems with T independent activation?

A
  • don’t generate memory
  • only become plasma cells that secrete IgM
  • functionally limited
36
Q

Where do B cells go after activation?

A

T-B border

37
Q

What happens at the T-B border?

A
  • some cells continue proliferation and become primary focus
  • remainder of B cells go back into follicle and become more antigen specific by becoming germinal center
38
Q

What happens to cells that become primary focus?

A
  • remain in T-B border and differentiate into plasma cells
39
Q

What do plasma cells from primary focus secrete?

A

IgM

40
Q

What happens after cells become plasma cells?

A

leave lymph node and go to fight infection

41
Q

What are germinal centers highly susceptible to?

A

apoptosis, so require survival signals from T(FH) cells to stay alive

42
Q

What does the germinal center develop into?

A

dark and light zone

43
Q

What happens in the dark zone?

A
  • proliferation of B cells
  • somatic hypermutation occurs
44
Q

What is somatic hypermutation?

A
  • an attempt to increase affinity of BCR for antigen
  • activation of activation induced cytidine deaminase (AID) which replaces a cytidine with a uridine, creating a U-G mismatch
45
Q

In what ways can a U-G mismatch be fixed?

A
  • replace U with C and have C-G again
  • replace U-G with A-T
  • remove U and fill gap with any nucleotide
  • excise larger stretch of DNA and fill gap
46
Q

What happens in the light zone?

A

B cells undergo selection which tests BCR receptor affinity for antigen

47
Q

How is BCR receptor affinity for antigen tested in light zone?

A

BCR binds antigen on follicular dendritic cells, internalizes the antigen, and presents it on MHC-II
- if no longer specific for antigen, undergoes apoptosisW

48
Q

What happens in the light zone if the cell is able to present antigen?

A

receive survival signals from T(FH) cells

49
Q

What signals do cells presenting antigen receive in light zone?

A
  • MHC-II/antigen binds TCR complex of TFH cell
  • CD40 on B cell binds CD40L on TFH cell
50
Q

What happens to the B cells that survive in the light zone?

A

can undergo class switch recombination

51
Q

What is class switch recombination?

A
  • cytokine signals result in activation of AID
  • AID creates double stranded breaks in switch regions of heavy chain class genes
  • this cuts out heavy class genes
52
Q

Do B cells stay in either dark or light zone?

A

no, they circulate between

53
Q

What eventually happens to cells in the light zone?

A

differentiate into memory cells or plasmablasts

54
Q

What happens after cells differentiate into plasmablasts?

A

leave lymph node and become plasma cells that secrete antibody

55
Q

How are Fc receptors diverse?

A
  • bind to different antibody classes
  • expressed by different cells
  • signal differently
56
Q

What do Fc receptors allow?

A

allow innate immune cells to be antigen specific

57
Q

Where are Fc receptors found?

A

innate immune cells

58
Q

What binds to the Fc receptor?

A

the Fc portion of the antibody

59
Q

When does signaling through Fc occur?

A

only when antigen is bound to Fab part of antibody

60
Q

What are the different functions of antibodies?

A
  • neutralizing agents
  • agglutination
  • opsonization
  • complement activation
  • antibody-dependent cell-mediated cytotoxicity
  • antibody-activated degranulation
61
Q

What do neutralizing agents do?

A
  • locks pathogen into past cells
  • antibody binds to viral proteins that would bind to cell membranes and give the virus entry to the cell
  • antibody binds to viral proteins, prevents virus from entering the cell
62
Q

What is agglutination?

A

the clumping of antigen using antibodies, making it harder to infect the cell

63
Q

How does agglutination occur?

A

multiple antibodies bind to many pathogens and cause a cluster of pathogens bound to antibodies

64
Q

What is opsonization?

A

marking antigen for phagocytosis

65
Q

How does opsonization occur?

A

antibody Fc binds to Fc receptor on phagocytic cell, induces phagocytosis
- phagocytic cell then engulfs antigen and antibody complex

66
Q

How does complement activation occur?

A

antibody bound to antigen, antibody then binds to complement initiator proteins, which initiates activation of complement via classical pathway

67
Q

How does antibody-activated degranulation occur?

A

antibody binds to antigen, which then binds to Fc receptor on granulocytes which then causes degranulation to happen

68
Q

Can IgM binds Fc?

A

no because expressed an pentameter

69
Q

What functions can IgM perform?

A

neutralization and agglutination

70
Q

Is IgM as antigen specific as other classes? Why or why not?

A

no because hasnt undergone somatic hypermutation

71
Q

What functions is IgG good at?

A

opsonization and ADCC and activate complement

72
Q

What is IgA secreted as in blood?

A

monomer

73
Q

What is IgA secreted in the blood good at?

A

ADCC

74
Q

What is IgA secreted as in bodily secretions?

A

dimer

75
Q

What functions is IgA effective at in bodily secretions?

A

neutralization and agglutination

76
Q

What is IgE effective at?

A

deglutination

Imunology (12 decks)

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