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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
Antigen-binding sites vary in?
Shape, size, and chemical properties to "fit" different epitopes
26
Epitopes can be...
- Linear: composed of AAs in sequence - Discontinuous: brought together when protein is folded
27
Antigen/antibody interactions are?
Noncovalent - Electrostatic forces, H bonds, van der Waals forces, hydrophobic interactions
28
Affinity
Binding strength of one antigen-binding site to its antigen - Different abs may bind to same antigen with varying affinity
29
Avidity
Overall strength of binding to multiple epitopes of an antigen
30
Monoclonal antibodies
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
31
Gene segments
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
32
Immunoglobulin genes
- 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)
33
Random recombination: L and C
Introns and exons, ready to be transcribed
34
Random recombination: V regions
Encoded by 2 Vl or 3 Vh gene segments - must be selected and rearranged to produce an exon.
35
Light chain V regon
1 variable (V) gene segment + 1 joining (J) gene segment
36
Heavy chain V region
1 variable (V) gene segment + 1 diversity (D) gene segment + 1 joining (J) gene segment
37
Somatic recombination
Process of bringing gene segments together during cell development
38
During B cell development, a single gene segment from each type brought together to form?
DNA sequence encoding V region of Ig chain
39
Somatic recombination: Light chain
single recombination b/t V (light) and J (light) segments
40
Somatic recombination: Heavy chain
two recombinations -- D joined to J (heavy) then DJ to V (heavy) segment
41
V, D, and J gene segments joined together are randomly selected, resulting in
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
Somatic
"Body"
43
Recombination signal sequences (RSSs)
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
V(D)J recombinase
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
Recombination follows which rule?
12/23 rule
46
12/23 rule
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
Coding joint
Ends of two gene segments joined
48
Signal joint
Ends of removed DNA joined
49
RAG has what type of activity?
Exonuclease
50
Junctional diversity
Contribution of P and N nucleotides to variation in coding joints - increases diversity by 3 x 10 ^7
51
Initial DNA cleavage generates?
Hairpins that are opened by DNA repair enzymes - nick in the hairpin occurs at random site - P (palindromic) nucleotides generated
52
Ends of hairpins can be modified by
Terminal deoxynucleotidyl transferase (TdT)
53
TdT
Randomly adds nucleotides...until we get complementarity - N nucleotides = not coded in germline
54
Exonucleases can remove what?
Nucleotides
55
Naive B cells
Circulating, haven't encountered antigen (not stimulated) - Express IgM and IgD on cell surface (don't express other isotypes
56
What produces the different isotypes?
Alternative splicing of same mRNA transcript
57
Allelic exclusion
*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
Antigen-binding sites formed by?
1 H chain and 1 L chain - random combinatorial association of one heavy chain with one light chain increases overall diversity of immunoglobulins
59
Heavy chains of IgM and IgD:
C-terminus hydrophobic sequence to associate with cell membranes, but very short cytoplasmic region
60
Ig alpha + Ig beta:
Travel with Ig from ER to cell surface; imp for signal transduction
61
B-cell receptor complex/B-cell receptor:
IgM or IgD + Ig alpha & Ig beta
62
Binding of antigen to Ig of a mature naive B cell...
Proliferation and differentiation, then antibody secretion
63
IgM produced in?
Large amounts
64
IgD produced in?
Respiratory tract
65
During differentiation, alternative RNA splicing results in?
Hydrophilic sequence in C-terminus of heavy chain
66
Somatic hypermutation
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
Activation-induced cytidine deaminase (AID)
Converts cytosine in single-stranded DNA to uracil - produced only in proliferating B cells - other enzymes convert U to one of four bases
68
Affinity maturation
Increase affinity for antigen
69
IgM is first class of antibody made in?
Primary immune response
70
Surface IgM is?
Monomeric
71
Secreted IgM is a?
Pentamer -- bulky, restricted in effector mechanism recruitment
72
Isotype (aka class) switching
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
Antibodies clear pathogens by?
- Neutralization - Opsonization - Activating complement
74
Neutralization
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
Opsonization
Phagocytes have receptors for Fc regions of some abs ex: Most abundant isotype in blood and lymph, very flexible
76
Activating complement
Direct lysis
77
IgE
Recruits effector functions of mast cells, basophils and eosinophils -- expel and kills parasites; causes allergies/asthma
78
IgD
Recruits basophils in the respiratory tract
79
IgA: subclasses
IgA1 & IgA2
80
IgG
IgG1, IgG2, IgG3, and IgG4 - Different effector functions ex: IgG3 best at activating complement
81
IgG4
Can exchange one H/L chain with another IgG4 - becomes monovalent - anti-inflammatory.

Immunology (6 decks)

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