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Microbiology & Immunology > 20-21 - Antibodies > Flashcards

20-21 - Antibodies Flashcards

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1
Q

Which of the following statements about antibodies is false?

a) Also known as Immunoglobulins (Ig)
b) They are a secreted glycoprotein
c) They are a secreted glycolipid
d) Structure includes constant and variable regions

A

Which of the following statements about antibodies is false?

a) Also known as Immunoglobulins (Ig)
b) They are a secreted glycoprotein

c) They are a secreted glycolipid

d) Structure includes constant and variable regions

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2
Q

IgG has a structure consisting of how many chains?

A

4

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3
Q

The light chains of IgG are bound to the heavy chain by…

A

A disulphide bridge

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4
Q

The variable region of IgG is located at the ( N / C) terminal.

A

The variable region of IgG is located at the N terminal.

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5
Q

How many antigen binding sites are present on 1 IgG molecule (and where are they located)?

A

IgG has 2 antigen binding sites.

They are located at the N-terminal end

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6
Q

IgG is:

a) Secreted but never membrane bound
b) Always membrane bound
c) Neither secreted nor membrane bound
d) Secreted or membrane bound

A

IgG is:

a) Secreted but never membrane bound
b) Always membrane bound
c) Neither secreted nor membrane bound

d) Secreted or membrane bound

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7
Q

Membrane bound IgG forms part of the which receptor?

A

B cell receptor (BCR)

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8
Q

Enzymatic clevage of Ig (for example with papain protease) occurs at which area of the antibody?

A

Hinge region

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9
Q

Enzymatic clevage of IgG by papain results in 3 fragments, namely…

A
  • 2x FAB (fragment, antigen binding)
  • 1x FC (fragment, crystalisable)
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10
Q

State the two purposes of antibodies…

A
  1. Bind specifically to epitopes on antigen/pathogen
  2. Recruit cells and molecules to destroy antigen/pathogen
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11
Q

By binding to epitopes on the antigen/pathogen, antibodies can achieve (2)…

A
  • Opsonisation (marking for phagocytosis)
  • Neutralisation (of toxins)
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12
Q

The effector function of antibodies is the recruitment of cell and molecules to destroy the antigen/pathogen to which it is bound. This is mediated by which region?

A

Fc (constant) region

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13
Q

The antigenic determinant of an antigen or pathogen is known as the…

A

Epitope

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14
Q

To which part of an antigen does an antibody bind?

A

The epitope

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15
Q

A multivalent antigen has multiple what?

A

Epitopes

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16
Q

Multivalent antigens have:

a) repeated epitopes
b) multiple epitopes (repeated or varied)
c) varied epitopes
d) 3 or more epitopes

A

Multivalent antigens have:

a) repeated epitopes

b) multiple epitopes (repeated or varied)

c) varied epitopes
d) 3 or more epitopes

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17
Q

Protein antigens

Epitopes can occur in two configurations…

A

Linear (continuous) or conformational (discontinuous)

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18
Q

Bonding between antibody and antigen is:

a) Always covalent
b) Never covalent
c) Sometimes covalent
d) Only due to electrostatic forces

A

Bonding between antibody and antigen is:

a) Always covalent

b) Never covalent

c) Sometimes covalent
d) Only due to electrostatic forces

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19
Q

Distinguish between affinity and avidity of antibody binding…

A

Affinity is the strength of binding between an antibody binding site and a single epitope

Avidity is the overall strength of binding between an antibody and antigen

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20
Q

Given the definition of avidity, multivalent antigens* have:

a) Higher avidity
b) Lower avidity
c) N/A (does not affect avidity)
d) No avidity

*assuming affinity of epitopes is constant

A

Given the definition of avidity, multivalent antigens have:

a) Higher avidity

b) Lower avidity
c) N/A (does not affect avidity)
d) No avidity

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21
Q

Summarise the main interactions of antibodies and the associated region (3)…

A
  • Bind to epitopes (V region)
  • Interaction with Fc receptors (C region)
  • Interaction with C1q to intiate complement (C region)
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22
Q

List 6 functions of antibodies…

A
  • Neutralisation
  • Agglutination
  • Opsonisation
  • Complement Activation
  • Degranulation by Fc receptor (FcR) (i.e. mast cells)
  • Cell recruitment by ADCC or activation of cells

ADCC = antibody dependent cellular cytotoxicity

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23
Q

Opsonisation may be either direct or indirect.

In direct opsonisation antibodies bind directly to Fc receptors.

Describe indirect opsonisation…

A

Binding of antibodies leads to an increase in complement deposition on the pathogen, which can bind to complement receptors on phagocytes.

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24
Q

An antibody-antigen complex can initiate the classical complement pathway by binding to…

A

C1qrs

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25
Q

Name 4 applications of antibodies in the lab…

A
  • Flow cytometry
  • Immunoprecipitation
  • Fluorescence microscopy
  • Western blot
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26
Q

What is the importance of the IgG variable region?

A

Gives rise to the binding specificity of the antigen

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27
Q

Give an example of a cell with Fc receptors (FcR)…

A
  • Mast cells (binding of antibody to FcR intiates degranulation)
  • B lymphocytes
  • NK cells
  • Macrophages
  • Neutrophils
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28
Q

What are the two main regions of an antibody if enzymatically cleaved with papain?

A

FAB (fragment, antigen binding) and FC (fragment, crystallisable)

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29
Q

Bound antibodies are known as…

A

SIg/BCR (secreted antibodies, B cell receptor)

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30
Q

Antigen binding sites are found at the variable region of the heavy and light chains. There are __ binding sites per IgG molecule.

A

Antigen binding sites are found at the variable region of the heavy and light chains. There are 2 binding sites per IgG molecule.

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31
Q

List the names of the domains found in IgG

(hint: there are 6 types)

A
  • Domains of constant region
    • CH1
    • CH2
    • CH3
    • CL
  • Domains of variable region
    • VH
    • VL
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32
Q

Glycosylation of IgG occurs at which domain?

A

CH2

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33
Q

Light domains (CL and VL)

Light domains are compact (around 100 amino acids) and comprised of…

A

2 sheets of β-strands with intrachain disulphide bonds

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34
Q

The antigen binding site is located at the…

a) variable region
b) hypervariable region
c) constant region
d) hinge region

A

The antigen binding site is located at the…

a) variable region

b) hypervariable region

c) constant region
d) hinge region

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35
Q

Hypervariable regions are also known as CDR, which stands for…

A

Complementarity-determining regions

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36
Q

How many loops of hypervariable region are found on each individual H or L chain?

A

3

37
Q

An antigen binding site is formed from how many CDRs in total?

A

6

(2 x 3)

38
Q

Domains can be described as…

A

Compactly folded globular units within proteins

39
Q

Ig Superfamily

Ig-like domains can also be found on other molecules. Give 4 examples…

A
  • T-cell receptors (TCR)
  • MHC molecules
  • Adhesion molecules
  • SIgnalling molecules
40
Q

The number of antigen binding sites per antibody is known as its…

A

Valency

41
Q

What are the five antibody isotypes?

A
  • IgM
  • IgA
  • IgD
  • IgG
  • IgE
42
Q

Where would you find IgA being produced?

A

In the epithelial cells (released in mucosal secretions)

43
Q

Which antibody isotype would increase in numbers in an allergic response?

A

IgE

44
Q

Which isotype exists as a pentamer?

A

IgM

45
Q

What needs to happen before antibody class switching can occur?

A

Antigen binding

46
Q

Which region of the antibody is affected by class switching?

A

CH (heavy chain of the constant region)

47
Q

Class switching (does / does not) affect antigen specificity of the antibody.

A

Class switching does not affect antigen specificity of the antibody.

(Variable regions, which include the antigen binding site, remain unchanged)

48
Q

Which is the most prevalent Ig in serum?

A

IgG

49
Q

Light chain come in two functionally identical forms, known as…

A

Kappa (κ) and lambda (ƛ)

(both light chains of a given antibody are always of the same type)

50
Q

IgM has a valency of…

A

10

51
Q

Where is IgM found in greatest abundance?

a) Liver
b) Blood
c) Placenta
d) Upper Respiratory Tract

A

Where is IgM found in greatest abundance?

a) Liver

b) Blood

c) Placenta
d) Upper Respiratory Tract

52
Q

Which is the first Ig isotype produced by neonates during the primary immune response?

(neonate = newborn child, an infant <4wks old)

A

IgM

53
Q

IgM monomers form pentamers by…

A

Binding covalently (disulphide bonds) to the J chain (joining chain)

54
Q

Explain, in terms of its structure, why IgM can have high avidity…

A

IgM forms a pentamer with a high valency (10). An ability to bind multiple epitopes increases its overall avidity.

55
Q

IgM has relatively low affinity because…

A

It is produced prior to affinity maturation

56
Q

List the 6 functions of IgM…

A
  • Activates classical complement pathway
  • Agglutination
  • Monomers can act as B cell receptors (BCR)
  • Produced rapidly for primary immune response
  • Protection from common pathogens
  • Protection of mucosal areas
57
Q

The heavy chains of IgG are comprised of __ domains of ____ chains.

A

The heavy chains of IgG are comprised of 4 domains of gamma chains.

58
Q

Production of which antibody isotype increases in the secondary immune response?

A

IgG

59
Q

What are the subclasses of IgG and how do they differ structurally?

A

IgG1-4

The structure varies in terms of the hinge region (see image)

60
Q

List the 4 functions of IgG…

A
  • Can activate classical complement pathway
  • Opsonisation
  • ADCC (antibody-dependent cell cytotoxicity)
  • Crossing the placenta
61
Q

IgG is the only antibody which…

A

Can cross the placenta

62
Q

IgA exists as a…

a) monomer in serum and secretions
b) monomer in serum and pentamer in secretions
c) monomer in serum and dimer in secretions
d) dimer in serum and monomer in secretions

A

IgA exists as a…

a) monomer in serum and secretions
b) monomer in serum and pentamer in secretions

c) monomer in serum and dimer in secretions

d) dimer in serum and monomer in secretions

63
Q

In its dimerised form, IgA is bound to…

A

J chain and secretory component

64
Q

Which antibody class is most prodominent in secretions/mucosa?

A

IgA

65
Q

Name the two subclasses of IgA and how they differ…

A

IgA1 (higher ratio in serum)

IgA2 (higher ratio in secretions)

(and they differ in their susceptability to bacterial proteases)

66
Q

The secretory component which binds to IgA dimers to aid their transport is made by which cells?

A

Epithelial cells

67
Q

List the 5 functions of IgA…

A
  • Inhibit microbial adherance to mucosal cells
  • Neutralise toxins and pathogens
  • Prevent commensurals from entering bloodstream
  • Intestinal protection of early neonates (present in early milk)
  • Opsonisation in the blood
68
Q

IgD and IgD are the only…

A

Co-expressed Igs

69
Q

IgD is present in ( low / high ) concentrations in serum.

A

IgD is present in low concentrations in serum.

70
Q

IgD may become membrane bound as part of…

A

B cell receptors (BCRs)

71
Q

IgD stimulates the release of antimicrobial peptides from which cell types?

A

Basophils and Mast Cells

72
Q

IgD is primarily…

A

Membrane bound

73
Q

IgD exists in what form?

A

Monomeric

74
Q

Which Ig isotype is most common in the brain?

A

There is no Ig found in the brain!

75
Q

IgE is the isotype with the ( lowest / highest ) concentration in the serum

A

IgE is the isotype with the lowest concentration in the serum

76
Q

Despite its low concentrations, IgE is highly potent in its effects. It binds with high affinity to…

A

Fc receptors (FcR) on basophils and mast cells

77
Q

IgE plays an important role in…

A

Asthma and allergies

78
Q

IgE induces basophils and eosinophils to release _______ and ________

IgE induces basophils and mast cells to release _____/______ _________

A

IgE induces basophils and eosinophils to release histamine and proteases

IgE induces basophils and mast cells to release vasoactive/inflammatory mediators

79
Q

As well as playing a role in allergies, IgE is important in ADCC which provides protection against which types of infection (2)?

(ADCC = antibody directed cell cytolysis)

A

Helminth and protozoan infections

80
Q

Describe how IgE leads to the release of histamine…

A
  • IgE binds to FcR of mast cell
  • Bound IgEs are cross-linked by a multivalent antigen
  • Granules (containing histamine) are released
81
Q

Distribution of Ig throughout the body

Pair these parts of the body with the abundant isotype(s) at that location…

  • Blood (2)
  • ECF (2)
  • Secretions and Breast Milk (1)
  • Foetus (1)
  • Subepithelial Mast Cells (1)
A

Distribution of Ig throughout the body

Pair these parts of the body with the abundant isotype(s) at that location…

  • Blood = IgG and IgM
  • ECF = IgG and IgA (monomeric)
  • Secretions and Breast Milk = IgA (dimeric)
  • Foetus = IgG
  • Subepithelial Mast Cells = IgE
82
Q

Anaphylaxis is a severe allergic reaction.

The increase in histamine, TNFα and vasodilation is a result of which isotype binding to which receptors on mast cells and basophils?

A

IgE binding to FcRs

83
Q

Name the treatment for anaphylaxis and give two effects of the treatment…

A

Adrenalin (via EpiPen), which increases vasoconstriction and blood glucose

84
Q

Class switching occurs ( before / during / after ) antigen stimulation.

A

Class switching occurs after antigen stimulation

85
Q

Class switching occurs through the irreversible…

A

Recombination of DNA

86
Q

The genes segments for the heavy chain isotypes (μ, α, δ, 𝛄, ε ) are located along the same region.

They are known as (1) and make this region of the genome (2)…

A
  1. Switch regions
  2. Modular
87
Q

Class switching allows the ___ isotype to switch to ________

A

Class switching allows the IgM isotype to switch to other isotypes

88
Q
A

Microbiology & Immunology (17 decks)

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