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Immunology > Chapter 4: Adaptive Immune - Antibody & B-Cell Diversity > Flashcards

Chapter 4: Adaptive Immune - Antibody & B-Cell Diversity Flashcards

1
Q

Immunoglobulin

A

Cell-surface B-cell antigen receptors & secreted antibodies

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2
Q

5 isotypes of immunoglobulins:

A

IgA, IgD, IgE, IgG, and IgM
- constant regions vary

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3
Q

Antibodies

A

Secreted form of B-cell immunoglobulin
- in blood, lymph, and on mucosal surfaces
- specific (bind to one antigen)

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4
Q

Function of antibodies?

A

Bind specific antigen and deliver to other immune components

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5
Q

Antibody repertoire

A

Individual’s total # of specific abs – as high as 10^16, closer to 10^9

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6
Q

Plasma cells

A

Effector B lymphocytes that secrete abs

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7
Q

Secreted antibodies from plasma cells…

A

B-cells must come before!

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8
Q

Antigen

A

molecular fragment/toxin/etc from a pathogen

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9
Q

How many antibodies secreted at a time of infection?

A

Multiple

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10
Q

B cell to Plasma cell

A
  1. Resting B cell
  2. Encounter with antigen
  3. Stimulated B cell (clonal selection) gives rise to antibody-secreting plasma cells
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11
Q

Antibody: general structure

A

*Glycoproteins made of 4 polypep chains
- 2 identical heavy chains & 2 identical light chains
- Arm
- variable (V) region —– antigen binding site
- constant region

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12
Q

Arm

A

L chain covalently linked to amino-terminal part of H chain
- Disulfide bonds link H-L & H-H

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13
Q

Variable (V) region

A

N-terminal area of L and H chains – amino acid sequence varies between different abs
—Antigen binding site: V regions of 1H & 1L

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14
Q

Constant region

A

Amino acid sequence similar b/t abs of same isotype
- similar to TIR of TLRs

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15
Q

Hinge region

A

Allows flexibility
- can be cleaved by proteases to form:
— Fragment antigen binding (Fab) region
— Fragment crystallizable (Fc) region

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16
Q

Fragment crystallizable (Fc) region

A

Effector function - binds to serum protein and cell surface receptors
—imp for cell recognition & elimination of pathogen

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17
Q

Isotypes

A
  • Ig isotype determined by C region of H chain
  • Hinge region, H chain length, and carb binding varies between isotypes
  • L chain isotypes: kappa or lambda
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18
Q

Immunoglobulin domain

A

Stable protein domain of ~100 AAs
- Variable domain
- Constant domain

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19
Q

Variable (V) domain

A

Vh and Vl
- Vh + Vl = antigen-binding site

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20
Q

Constant (C) domain

A
  • One Cl per light chain
  • 3-4 Ch per heavy chain
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21
Q

Hypervariable (HV) regions

A

Regions of V domains that have variable amino acid sequences
- aka complementary-determining regions (CDRs)
- 3 domain

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22
Q

Framework regions

A

Less variable regions of V domains

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23
Q

Epitope

A

Part of the antigen to which an antibody binds
- usually carbs or proteins
- multivalent

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24
Q

Multivalent

A

Antigen with more than one epitope or multiple copies of same epitope

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25
Q

Antigen-binding sites vary in?

A

Shape, size, and chemical properties to “fit” different epitopes

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26
Q

Epitopes can be…

A
  • Linear: composed of AAs in sequence
  • Discontinuous: brought together when protein is folded
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27
Q

Antigen/antibody interactions are?

A

Noncovalent
- Electrostatic forces, H bonds, van der Waals forces, hydrophobic interactions

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28
Q

Affinity

A

Binding strength of one antigen-binding site to its antigen
- Different abs may bind to same antigen with varying affinity

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29
Q

Avidity

A

Overall strength of binding to multiple epitopes of an antigen

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30
Q

Monoclonal antibodies

A
  1. Fusion of B cells from mouse immunized q antigen & myeloma cells
  2. Grow in drug-containing medium (only hybrid cells live)
  3. Select for antigen-specific hybridoma
  4. Clone the selected hybridoma cells
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31
Q

Gene segments

A

Fragments of genes across a chromosome that must come together to be expressed
- all cells have fragmented Ig heavy- and light-chain loci
— Germline form/config
— Only B cells can rearrange & assemble the functional Ig gene
——occurs during B cell development from B-cell precursors in bone marrow

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32
Q

Immunoglobulin genes

A
  • Heavy-chain locus – chrom 14
  • Kappa light-chain locus – chrom 2
  • Lambda light-chain locus – chrom 22
    — diff segments encode leader peptide (L), V region (V), and constant region (C)
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33
Q

Random recombination: L and C

A

Introns and exons, ready to be transcribed

34
Q

Random recombination: V regions

A

Encoded by 2 Vl or 3 Vh gene segments - must be selected and rearranged to produce an exon.

35
Q

Light chain V regon

A

1 variable (V) gene segment + 1 joining (J) gene segment

36
Q

Heavy chain V region

A

1 variable (V) gene segment + 1 diversity (D) gene segment + 1 joining (J) gene segment

37
Q

Somatic recombination

A

Process of bringing gene segments together during cell development

38
Q

During B cell development, a single gene segment from each type brought together to form?

A

DNA sequence encoding V region of Ig chain

39
Q

Somatic recombination: Light chain

A

single recombination b/t V (light) and J (light) segments

40
Q

Somatic recombination: Heavy chain

A

two recombinations – D joined to J (heavy) then DJ to V (heavy) segment

41
Q

V, D, and J gene segments joined together are randomly selected, resulting in

A

Diversity of Ig V regions
- 295 diff light chains possible
- 5520 diff heavy chains possible
- randomly combines = 1.6 million diff antibodies
—–abs repertoire = 10^9

42
Q

Somatic

A

“Body”

43
Q

Recombination signal sequences (RSSs)

A

Direct the recombination of the V, J, and D gene segments
- Flank 3’ side of V, both sides of D, and 5’ side of J

44
Q

V(D)J recombinase

A

Set of enzymes that recombines V,D, and J gene segments
- “chopping up DNA”
- 2 of the components: recombination-activating genes (RAG) 1 and 2 – only made in developing lymphocytes

45
Q

Recombination follows which rule?

A

12/23 rule

46
Q

12/23 rule

A

RAG complex binds to an RSS and recruits the other RSS to the complex…RAG cleaves DNA…Coding joint or signal joint
- DNA is bent
- 23 always combines with 12

47
Q

Coding joint

A

Ends of two gene segments joined

48
Q

Signal joint

A

Ends of removed DNA joined

49
Q

RAG has what type of activity?

A

Exonuclease

50
Q

Junctional diversity

A

Contribution of P and N nucleotides to variation in coding joints
- increases diversity by 3 x 10 ^7

51
Q

Initial DNA cleavage generates?

A

Hairpins that are opened by DNA repair enzymes
- nick in the hairpin occurs at random site
- P (palindromic) nucleotides generated

52
Q

Ends of hairpins can be modified by

A

Terminal deoxynucleotidyl transferase (TdT)

53
Q

TdT

A

Randomly adds nucleotides…until we get complementarity
- N nucleotides = not coded in germline

54
Q

Exonucleases can remove what?

A

Nucleotides

55
Q

Naive B cells

A

Circulating, haven’t encountered antigen (not stimulated)
- Express IgM and IgD on cell surface (don’t express other isotypes

56
Q

What produces the different isotypes?

A

Alternative splicing of same mRNA transcript

57
Q

Allelic exclusion

A

*Immunoglobulin diversity #4
Expression of only one heavy chain and one light chain by a single B cell
- ensures B cell produces IgM and IgD specific to a single antigen

58
Q

Antigen-binding sites formed by?

A

1 H chain and 1 L chain
- random combinatorial association of one heavy chain with one light chain increases overall diversity of immunoglobulins

59
Q

Heavy chains of IgM and IgD:

A

C-terminus hydrophobic sequence to associate with cell membranes, but very short cytoplasmic region

60
Q

Ig alpha + Ig beta:

A

Travel with Ig from ER to cell surface; imp for signal transduction

61
Q

B-cell receptor complex/B-cell receptor:

A

IgM or IgD + Ig alpha & Ig beta

62
Q

Binding of antigen to Ig of a mature naive B cell…

A

Proliferation and differentiation, then antibody secretion

63
Q

IgM produced in?

A

Large amounts

64
Q

IgD produced in?

A

Respiratory tract

65
Q

During differentiation, alternative RNA splicing results in?

A

Hydrophilic sequence in C-terminus of heavy chain

66
Q

Somatic hypermutation

A

Single-nucleotide substitutions introduced randomly into V-domain coding sequence
- occurs after antigen binding
- Activation-induced cytidine deaminase (AID)
- may increase affinity for antigen

67
Q

Activation-induced cytidine deaminase (AID)

A

Converts cytosine in single-stranded DNA to uracil
- produced only in proliferating B cells
- other enzymes convert U to one of four bases

68
Q

Affinity maturation

A

Increase affinity for antigen

69
Q

IgM is first class of antibody made in?

A

Primary immune response

70
Q

Surface IgM is?

A

Monomeric

71
Q

Secreted IgM is a?

A

Pentamer – bulky, restricted in effector mechanism recruitment

72
Q

Isotype (aka class) switching

A

Further DNA recombination events allows V-region to combine with other heavy-chain C genes
- only in B cells responding to antigen
- previously expressed C gene is cleaved and new gene is transcribed
- patterns of isotype switching regulated by cytokines secreted by other immune cells

73
Q

Antibodies clear pathogens by?

A
  • Neutralization
  • Opsonization
  • Activating complement
74
Q

Neutralization

A

Directly inactivating a pathogen/toxin and preventing it from interacting with human cells — *neutralizing antibodies
ex: Dimeric IgA = secreted in gut, milk, saliva, sweat, tears

75
Q

Opsonization

A

Phagocytes have receptors for Fc regions of some abs
ex: Most abundant isotype in blood and lymph, very flexible

76
Q

Activating complement

A

Direct lysis

77
Q

IgE

A

Recruits effector functions of mast cells, basophils and eosinophils – expel and kills parasites; causes allergies/asthma

78
Q

IgD

A

Recruits basophils in the respiratory tract

79
Q

IgA: subclasses

A

IgA1 & IgA2

80
Q

IgG

A

IgG1, IgG2, IgG3, and IgG4
- Different effector functions
ex: IgG3 best at activating complement

81
Q

IgG4

A

Can exchange one H/L chain with another IgG4
- becomes monovalent
- anti-inflammatory.

Immunology (6 decks)

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