B Cells

Question 1

What is the major function of B cells?

Answer 1

produce antibodies (immunoglobulins)

Question 2

What is a surface immunoglobulin?

Answer 2

B cell antigen receptor that is membrane bound

Question 3

What is valency?

Answer 3

number of antigen-binding sites within one receptor

Question 4

What are isotypes?

Answer 4

various kinds of antibodies with different major functions

Question 5

What are the chains of antibodies?

Answer 5

light chain, heavy chain

Question 6

What does the hinge region do?

Answer 6

holds two heavy chains together by disulfide bonds

Question 7

What are the aspects of the variable region?

Answer 7

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

Question 8

What are the aspects of the constant region?

Answer 8

at C terminus, do NOT influence specificity

Question 9

What is the Fc portion or fragment?

Answer 9

fragment crystalizable, confers important effector functions of secreted antibodies

Question 10

What is the Fab’ portion?

Answer 10

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

Question 11

How are the 5 isotypes grouped?

Answer 11

based on the constant region of their heavy chains

Question 12

Which isotypes are subtyped?

Answer 12

IgG & IgA (General Authority)

Question 13

Why do effector functions of isotypes differ?

Answer 13

they have different constant regions

Question 14

Do variable regions influence the isotype?

Answer 14

NO

Question 15

Do light chains influence the isotype?

Answer 15

NO

Question 16

What isotype is rarely secreted?

Answer 16

IgD

Question 17

What determines membrane or secreted forms of antibodies?

Answer 17

C terminus of heavy chain

Question 18

What is a J chain?

Answer 18

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

Question 19

What is the valence of IgM and IgA?

Answer 19

IgM = 10, IgA = 4

Question 20

What antibody is part of the mucosal immune system?

Answer 20

dimeric IgA

Question 21

What provides primary signal for B cell activation?

Answer 21

surface immunoglobulins with antigen bound

Question 22

What is neutralization?

Answer 22

prevention of harmful agents interacting with host cells

Question 23

What mediates neutralization?

Answer 23

variable regions

Question 24

What is opsonization?

Answer 24

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

Question 25

What is antibody-dependent cell-mediated cytotoxicity?

Answer 25

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

Question 26

What do mast cells & basophils express?

Answer 26

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

Question 27

What antibodies are involved in neonatal immunity?

Answer 27

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

Question 28

Describe transcytosis of IgA

Answer 28

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

Question 29

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

Answer 29

protecting it from degradation so it can survive in saliva

Question 30

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

Answer 30

IgG, IgA

Question 31

What is the first expressed isoptype?

Answer 31

IgM

Question 32

What are naive B cells?

Answer 32

have not yet encountered antigen

Question 33

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

Answer 33

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

Question 34

What do plasma cells secrete?

Answer 34

pentameric IgM, rarely IgD

Question 35

What do plasma cells NOT express?

Answer 35

surface immunoglobulins

Question 36

What main antibodies do isotype switching?

Answer 36

IgG for systemic immunity | dimeric IgA for mucosal immunity

Question 37

What isotype do plasma/memory cell express?

Answer 37

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

Question 38

What are T-independent antigens?

Answer 38

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

Question 39

What do T-independent antigens bypass?

Answer 39

the need for costimulatory signal via CD40

Question 40

What antibody results from T-independent antigens?

Answer 40

low affinity IgM, few memory cells generated

Question 41

What do helper T cells do?

Answer 41

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

Question 42

What do cytokines do?

Answer 42

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

Question 43

What responds during secondary response?

Answer 43

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

Question 44

What is affinity maturation?

Answer 44

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

Question 45

What is somatic hypermutation?

Answer 45

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

Question 46

What is isotype switching? what is the outcome?

Answer 46

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

Question 47

How does isotype switching occur?

Answer 47

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

Question 48

Why is isotype switching called permanent?

Answer 48

because those cells can never express IgM or IgD again

Question 49

What increased diversity of the variable region?

Answer 49

multiple V, J and D gene segments

Question 50

Where does DNA reorganize by recombination?

Answer 50

precursor B cells in bone marrow

Question 51

How can recombination occur for light and heavy chains?

Answer 51

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

Question 52

How is the repair of gap described?

Answer 52

sloppy, further increased diversity

Question 53

How is the diversity process described?

Answer 53

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