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Micro > B Cells > Flashcards

B Cells Flashcards

1
Q

What is the major function of B cells?

A

produce antibodies (immunoglobulins)

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2
Q

What is a surface immunoglobulin?

A

B cell antigen receptor that is membrane bound

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3
Q

What is valency?

A

number of antigen-binding sites within one receptor

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4
Q

What are isotypes?

A

various kinds of antibodies with different major functions

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5
Q

What are the chains of antibodies?

A

light chain, heavy chain

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6
Q

What does the hinge region do?

A

holds two heavy chains together by disulfide bonds

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7
Q

What are the aspects of the variable region?

A

tremendous variation determining antigen specificity, contribution from light and heavy chain form antigen-binding site, “basic unit” has 2 identical antigen-binding sites (bivalent)

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8
Q

What are the aspects of the constant region?

A

at C terminus, do NOT influence specificity

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9
Q

What is the Fc portion or fragment?

A

fragment crystalizable, confers important effector functions of secreted antibodies

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10
Q

What is the Fab’ portion?

A

fragment antigen binding, light chain and one region from both the variable and constant domains of the heavy chain, forms one complete antigen-binding site

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11
Q

How are the 5 isotypes grouped?

A

based on the constant region of their heavy chains

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12
Q

Which isotypes are subtyped?

A

IgG & IgA (General Authority)

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13
Q

Why do effector functions of isotypes differ?

A

they have different constant regions

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14
Q

Do variable regions influence the isotype?

A

NO

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15
Q

Do light chains influence the isotype?

A

NO

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16
Q

What isotype is rarely secreted?

A

IgD

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17
Q

What determines membrane or secreted forms of antibodies?

A

C terminus of heavy chain

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18
Q

What is a J chain?

A

disulfide bonds joins 5 IgM for a pentamer, and 2 IgA for dimer

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19
Q

What is the valence of IgM and IgA?

A

IgM = 10, IgA = 4

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20
Q

What antibody is part of the mucosal immune system?

A

dimeric IgA

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21
Q

What provides primary signal for B cell activation?

A

surface immunoglobulins with antigen bound

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22
Q

What is neutralization?

A

prevention of harmful agents interacting with host cells

23
Q

What mediates neutralization?

A

variable regions

24
Q

What is opsonization?

A

like complement, antibodies coat pathogen promoting phagocytosis by macrophages and neutrophils

25
Q

What is antibody-dependent cell-mediated cytotoxicity?

A

ADCC, NK cells express Fc receptors for IgG, find cells coated with antibodies and bind/kill them

26
Q

What do mast cells & basophils express?

A

Fc receptors for IgE, histamine and other mediators causing an allergic reaction

27
Q

What antibodies are involved in neonatal immunity?

A

IgG crosses placenta, IgA is in breast milk; bot provide passive immunity to newborns/infants

28
Q

Describe transcytosis of IgA

A

endothelial cells express poly-Ig receptors that bind dimeric IgA; they are endocytosed and transported through cell; in lumen IgA is released with secretory component/piece remains attached to IgA protecting it from degradation

29
Q

What is the function of the secretory component/piece remaining attached to IgA

A

protecting it from degradation so it can survive in saliva

30
Q

What is the predominate isotype in serum & lymph? mucosal secretions?

A

IgG, IgA

31
Q

What is the first expressed isoptype?

A

IgM

32
Q

What are naive B cells?

A

have not yet encountered antigen

33
Q

What do mature naive B cells express on the cell surface? how are they similar and expressed?

A

IgM & IgD
same antigen specificity
co-expression is due to mRNA processing

34
Q

What do plasma cells secrete?

A

pentameric IgM, rarely IgD

35
Q

What do plasma cells NOT express?

A

surface immunoglobulins

36
Q

What main antibodies do isotype switching?

A

IgG for systemic immunity

dimeric IgA for mucosal immunity

37
Q

What isotype do plasma/memory cell express?

A

the resulting isotype switched isotype with the same specificity as IgM & IgD

38
Q

What are T-independent antigens?

A

B cells responding to some antigens without interacting with helper T cells

39
Q

What do T-independent antigens bypass?

A

the need for costimulatory signal via CD40

40
Q

What antibody results from T-independent antigens?

A

low affinity IgM, few memory cells generated

41
Q

What do helper T cells do?

A

provide B cells with costimulatory signal (#2) via CD40 & secrete cytokines

42
Q

What do cytokines do?

A

promote B cell proliferation, isotype change, and memory B cell development

43
Q

What responds during secondary response?

A

memory B cells; plasma cells secrete IgG or IgA with changing effector functions from isotype switching based on secreted antibodies

44
Q

What is affinity maturation?

A

where antibodies gain higher affinity for antigens during the course of an immune response

45
Q

What is somatic hypermutation?

A

variable region genes of light and heavy chains undergo point mutations, some have increased affinity

46
Q

What is isotype switching? what is the outcome?

A

change from IgM to another isotype, only constant region of heavy chain, antigen specificity remains the same

47
Q

How does isotype switching occur?

A

the mue switch region pairs with another switch region forming a loop which is then excised (deleted)

48
Q

Why is isotype switching called permanent?

A

because those cells can never express IgM or IgD again

49
Q

What increased diversity of the variable region?

A

multiple V, J and D gene segments

50
Q

Where does DNA reorganize by recombination?

A

precursor B cells in bone marrow

51
Q

How can recombination occur for light and heavy chains?

A

light: any V and virtually any J can recombine = one rearrangement
heavy: any V, D, and J can recombine = two rearrangements

52
Q

How is the repair of gap described?

A

sloppy, further increased diversity

53
Q

How is the diversity process described?

A

random and independent of antigen; the shuffling of the gene segments is the main contributor to antibody diversity

Micro (8 decks)

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