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Infection and Immunity > Antibody interaction with antigen > Flashcards

Antibody interaction with antigen Flashcards

1
Q

What does the Ab recognise?

A

Conformational antigens composed of several sequentially discontinuous segments brought together by folding of the molecule

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2
Q

What is the epitope?

A

The part of the antigen which is recognized by the antibody

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3
Q

What is the paratope?

A

The complimentary part of the antibody

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4
Q

What is each V region made of?

A

3 hypervariable regions

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5
Q

What are complimentary determining regions?

A

6 hypervariable regions of light and heavy chains

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6
Q

Describe the hypervariable region

A

CDR loops interact with antigen
Poke out of the beta sheets of Ig domain

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7
Q

How does the binding happen?

A

Neither the antibody nor the antigen is changed by binding
One antibody binding site binds to one epitope on the antigen
The binding is non-covalent and is reversible

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8
Q

What bonds are involved in the binding?

A

Non-covalent interaction due to Ionic bonds
H-bonds
Hydrophobic bonds
Van der Waals forces
Lots of small forces add up to a strong interaction.
All critically dependent on the distance apart

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9
Q

What forces are present in antibody-antigen binding?

A

Electrostatic
Hydrogen bonds
Hydrophobic bonds
Van der Waals

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10
Q

What is the strength of interaction?

A

Each force acts over short distance that can be measured (affinity)

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11
Q

What is meant by avidity?

A

Avidity = total binding strength
Different from affinity (binding strength at a single binding site)
Avidity functionally more important than affinity

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12
Q

What else is required for antibody production?

A

Additional signals from the B cell once BCR is ligated and IgAlpha and IgBeta signal is sent

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13
Q

How do T cells contribute to Ab production?

A

Cytokine production

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14
Q

What does neutralisation of viruses depend on?

A

type of virus, target cell and class of Ab

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15
Q

What is the importance of antibodies in neutralisation?

A

May be important in limiting viral infectivity - bind to a virus to block infection
Vaccine efficacy often assessed by measuring circulating, neutralising Abs

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16
Q

Why is neutralisation important?

A

May inhibit virus-cell interaction
Prevent endocytosis of virus
Prevent uncoating inside endosome

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17
Q

What makes neutralisation more effective?

A

Complement

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18
Q

How are toxins neutralised?

A

Abs bind bacterial exotoxins: neutralise their effect by preventing attachment to cellular receptors (e.g. binding of cholera toxin to ganglioside GM1)

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19
Q

What antibodies are important in neutralisation?

A

IgG and IgA

20
Q

What receptor mediates toxin clearance?

A

Fc-receptor

21
Q

What is opsonisation?

A

The coating (binding) of particles by either Ab,
complement or APP (eg CRP)
Ab bind microorganisms via the Fab and to cells
by the Fc

22
Q

What does opsonisation do?

A

Increases the efficiency of the
phagocytic process, allowing the organism to be
cleared more effectively

23
Q

What is complement?

A

The complement system is a collection of circulating membrane-associated proteins
Important in defence against microbes

24
Q

What are the pathways of complement?

A

Classical and alternate pathways

25
Q

What are the functions of complement?

A

Chemotaxis
Opsonisation
Lysis of target cells
Priming of adaptive immune response

26
Q

How do antibodies interact with cells?

A

Via Fc receptors

27
Q

What do Fc receptors associate with?

A

G-chain

28
Q

How does activation of Fc receptors occur?

A

Due to aggregation of receptors and signalling via Immunoreceptor Tyrosine-
based Activation or Inhibition Motifs

29
Q

What does Fc receptor activation cause?

A

ADCC (antibody-dependent cellular cytotoxicity)
Phagocytosis
Apoptosis
Mediator release
Can enhance antigen presentation

30
Q

What does CD64 bind?

A

Monomeric IgG1 and IgG3 with high affinity and IgG4 with low affinity
No binding to IgG2

31
Q

Where is CD64 expressed?

A

On mononuclear phagocytes

32
Q

What is CD64 involved in?

A

Phagocytosis of immune complexes and mediator release

33
Q

What is the structure of CD64?

A

3 extracellular Ig domains
Associated with gamma chain ITAM

34
Q

Describe CD32

A

2 types = FcgRIIa and FcgRIIb

35
Q

Describe FcgRIIa

A

Wide cellular distribution
Moderate affinity for monomeric IgG1 and IgG3.
High affinity for complexed IgG
Has ITAM

36
Q

Describe FcgRIIb

A

Same specificity for Ig but has ITIM

37
Q

How is the antibody response inhibited?

A

Secreted antibody forms complex with antigen
Antigen-antibody complex binds to B cell Ig and Fc receptor
Block in B cell receptor signalling due to ITIM -ve signal
Inhibition of B cell response

38
Q

Describe CD16

A

Has FcgRIIIa and FcgRIIIb

39
Q

Describe FcgRIIIa

A

Transmembrane molecule with moderate affinity for monomeric IgG
Associated with g-, b-, z- h- chains of the CD3 complex as ITAMs
Expressed on monocytes, macrophages, NK cells and some T cells
ADCC

40
Q

Describe FcgRIIIb

A

GPI (glycophosphatidilelinositol) linked with low affinity for monomeric IgG
Expressed on neutrophils and basophils
Activates by lipid raft formation and associates

41
Q

Describe CD89

A

Associated with g-chain
Expressed on myeloid cells
Can trigger phagocytosis, cell lysis and the release of inflammatory mediators
Binds both IgA1 and IgA2

42
Q

Describe Fc-epsilon-RI

A

Very high affinity receptor for IgE
Associates with g-chains and b-chain (abg2
receptor unit)
Expressed on mast cells and basophils.
Receptors always saturated (low serum IgE)
X-linking of these Ab molecules bound to FceRI
leads to mediator release e.g histamine

43
Q

Describe CD23

A

Low affinity receptor for IgE
Expressed on leukocytes and lymphocytes.
Not a member of the Ig-Superfamily, similar to C-type lectins (eg mannose binding lectin)

44
Q

Where is CD23a expressed?

A

B cells and involved in IgE production

45
Q

Where is CD23b expressed?

A

Many cell types and induced by IL-4

Infection and Immunity (33 decks)

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