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2.1 Molecular Immunology > Greg - Antibody Structure > Flashcards

Greg - Antibody Structure Flashcards

1
Q

What are antibodies?

A

Glycoprotein molecules

Produced by plasma cells

They bind to antigenic targets

They are also called immunoglobubins/gamma globulins

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2
Q

What are antibodies?

A

Glycoprotein molecules

Produced by plasma cells

They bind to antigenic targets

They are also called immunoglobulins/gamma globulins

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3
Q

What is a glycoprotein?

A

A protein with a carbohydrate post translation modification

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4
Q

How can antibodies neutralise/block entry of pathogens?

A

Antibody against viral surface proteins block entry to human cell by binding to the protein - prevents it from binding to host’s cell

= neutralisation

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5
Q

Explain agglutination/precipitation
(3)

A

Antibodies can clump antigens together into an immune complex for removal

Agglutination = insoluble target

Precipitation = soluble target

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6
Q

What effector functions do antibodies have?
(3)

A

Activate complement
Aid phagocytosis via opsonisation
Mediate antibody mediated cellular cytotoxicity by NKCs

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7
Q

List the functions of antibodies
(5)

A

Block entry/neutralisation of pathogen

Agglutination/precipitation

Complement activation

Opsonisation

Aids NKCs

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8
Q

What is a myeloma?

A

Cancer of plasma cells
i.e. one plasma cell keeps producing it’s antibody continuously

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9
Q

Why were antibodies hard to study?

A

Due to their heterogenous nature i.e. they are all different

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10
Q

What research allowed us to study antibodies?

A

Studies of myelomas as these cells produce a monoclonal antibody population which is identical and can therefore be separated and studied

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11
Q

How are the different parts of an antibody examined?
(3)

A

We cleave the antibody into parts

Papain cleaves the antibody at the middle and creates three fragments - we can then make crystals of Fc because the Fc molecule is the same in every antibody (uniform) -> can examine Fc now

Pepsin cleaves antibody at hinge - gives us a F(ab’)2 with the hinge and a partial Fc fragment (pFc) - research can now be carried out on the Fab

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12
Q

What joins the light and heavy chains of an antibody?

A

Disulphide bonds between cysteine residues

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13
Q

What does mercaptoethanol do to antibodies?
(3)

A

This chemical destroys the disulfide bridges between the light and heavy chains

The four chains fall apart

This gives us 2 heavy chains and 2 light chains which can be examined further

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14
Q

What are the two types of disulphide bonds?

A

Inter-chains
Intra-chains

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15
Q

List the variable and constant regions

A

VL & CL

VH & CH

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16
Q

List the parts of an antibody
(7)

A

Fab region

Fc region

Intra-chain

Inter-chain

Variable region

Hinge region

Constant region

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17
Q

What is the hinge region?
(3)

A

Part of the molecule that can move

It gives the antibody some flexibility

It makes binding to antigens easier

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18
Q

The functions of the antibody molecule are spatially segregated, what does this mean?

A

Some functions of antibodies relate only to the Fab region while others relate only to the Fc region

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19
Q

What function is the Fab site responsible for?

A

Antigen binding

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20
Q

What functions is the Fc site responsible for?
(3)

A

Complement binding site

Binding to Fc receptors

Placental transfer

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21
Q

Write about the antibody-antigen reaction?
(2)

A

A non-covalent bond
Reversible reaction - i.e. antigen has affinity for antibody but can be pulled apart

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22
Q

What is affinity in terms of antigens?

A

The strength of the reaction between a single antigenic determinant and a single combining site

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23
Q

What is avidity in terms of antigens?

A

The overall strength of binding between antigen with many determinants and multivalent antibodies

The total attractive force = the total affinity

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24
Q

What type of antibody is first made by plasma cells?

A

IgM

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25
Q

What is specificity?

A

The ability of an antibody binding site to react with only one antigenic deteminant

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26
Q

What is cross-reactivity?

A

The ability of an individual antibody binding site to react with more than one antigenic determinant

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27
Q

What is an epitope?

A

Regions of an antigen recognized by B cell antibody and T cell receptor

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28
Q

What is the difference between T cell dependant antibody production and T cell independent antibody production?

A

T-dependent results in high affinity antibodies, memory B cells, longer lived plasma cells, and isotype switching of antibodies (i.e. switch from IgM)

T-independent results in low affinity antibodies, short lived plasma cells and mainly IgM antibodies

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29
Q

What determines the classes or isotypes of antibodies?

A

Their heavy chain amino acid sequences

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30
Q

List the five antibody isotypes and their heavy chains

A

IgG - Gamma heavy chain
IgA - alpha heavy chain
IgM - mu heavy chain
IgD - delta heavy chain
IgE - epsilon heavy chain

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31
Q

Where is IgD found?

A

The surface of B cell receptors where it acts as a receptor

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32
Q

Where is IgA found?

A

The IgA monomer is found in blood but the dimer is found on cell surfaces

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33
Q

What determines amino acid subclasses?

A

Heavy chain amino acid sequences

34
Q

How many subclasses does IgG have?

A

4

35
Q

What are the four main igG subclasses?

A

IgG1 -> gamma 1 heavy chain

IgG2 -> gamma 2 heavy chain

IgG3 -> gamma 3 heavy chain

IgG4 -> gamma 4 heavy chain

36
Q

How many subclasses does IgA have?

A

2

37
Q

What are the subclasses for IgA?

A

IgA1 -> alpha 1 heavy chain
IgA2 -> alpha 2 heavy chain

38
Q

How are the types of light chains determined?

A

They are determined by sequence

Either kappa (K) or lambda

39
Q

How many kappa subtypes are there?

A

None

40
Q

How many lambda subtypes are there?

A

1-4 subtypes

41
Q

How would IgA , subtype 1, lambda 2 be written?

A

IgA1(lamda2)

42
Q

List the subtypes of IgG in order of population?

A

IgG1

IgG2

IgG3 = IgG4

43
Q

How much of the gamma globulins in serum are IgG?

A

80%

44
Q

What is the only class of antibody that can cross the placenta?

A

IgG2

45
Q

What subtypes of IgG can fix complement?

A

IgG3 and IgG4

46
Q

Which IgG subtypes act as opsonins and how?

A

IgG2 and IgG3 act as opsonins

They can be bound by the Fcgamma receptor

47
Q

What is responsible for the long serum half-life of IgG?

A

FcRn

48
Q

What is FcRn?

A

The neonatal Fc receptor for IgG2

49
Q

Describe the structure of IgA in secretions

A

A dimer with a J-chain and secretory component (hence why it’s found in secretions)

50
Q

Hoe much of the gamma globulins in serum are IgA

A

Between 10 and 15 percent

51
Q

List some places IgA can be found
(3)

A

Saliva
Breast milk
Tears

52
Q

What is the J-chain of IgA similar to?

A

Similar to the J-chain of IgM

53
Q

Write a note on the structure of IgM
(5)

A

Pentameric in serum but a monomer on B-cell surface

In pentamer - all light and heavy chains are identical

Extra domain (CH4)

J chain

Valency of 10

54
Q

What is the extra domain in IgM called?

A

CH4

55
Q

Write about the properties of IgM
(5)

A

3rd highest concentration in serum
First Ig made by foetus and B cells
Best complement fixer
Agglutination
IgMFc receptor -> binds Fc receptors on B cells
Anchors in B cell membrane but must partner with other proteins on the surface to act as a receptor and activate the cell

56
Q

Write about IgE structure
(3)

A

Monomer in structure
Extra CH4 domain
Only survives for 2 and a half days

57
Q

Write about the properties of IgE
(6)

A

Very potent activity
Very low serum concentrations
Hypersensitivity reactions
Hay fever, asthma hives etc
Binds Fce receptors on basophils and mast cells (degranulation)
Anti-parasitic defence

58
Q

Explain what happens in an allergic reaction

A

IgE has been produced against a harmless environmental molecule

When you first come across the allergen you won’t have a reaction but IgE will be made and it will bind to Fc epsilon receptors on mast cells -> next time you meet the allergen the IgE will cross bind and send an activation into the mast cell which releases histamine

59
Q

Write about the structure and properties of IgD
(5)

A

Monomer
Tail piece to be anchored in B cell membrane along with IgM
2nd lowest concentration in blood
Most ancient antibody class
We though it had no function but now see it is produced in the lower respiratory tract during infection

60
Q

What do most cells express that act as receptors for the Fc portions of antbiodies

A

Glycoprotin

61
Q

What do most cells express that act as receptors for the Fc portions of antbiodies

A

Glycoprotiens

62
Q

Why are Fc receptors needed on cells?

A

Opsonisation
Antibody-dependent cellular cytotoxicity
Cell activation
Cell differentiation

63
Q

What is the requirement to be part of the immunoglobulin superfamily

A

Must have at least one domain homologous to other members

e.g. Immunoglobulin-fold domain structure

64
Q

Why might specificity be measured in the lab?

A

Chemical methods could not distinguish between similar proteins (e.g. Human vs. pig insulin) but antibodies can do this absolutely

65
Q

Why might avidity be used in the lab?

A

Affinity dictates the effectiveness of an antibody. For example, the higher the affinity of an antibody, the less you might need for a procedure

66
Q

Under what conditions might patient antibodies be measured?

A

Inflammation/infection
Cancer
Allergy
Parasitic infection
Immunodeficiency
Autoimmunity

67
Q

Why might antibodies be measured during inflammation?

A

Due to increase in antibody response due to immune responses

68
Q

Why might antibodies be measured during cancer?

A

Cancer of B cells result in monoclonal antibody type

69
Q

Why might antibodies be measured during allergic reaction

A

Increase in IgE
Increase in specific IgE

70
Q

Why might antibodies be measured during parasitic infection

A

Increased total IgE

71
Q

Why might antibodies be measured in immunodeficiency

A

Can the patient make normal levels of all antibody classes?

72
Q

Why might antibodies be measured during autoimmunity

A

What antibody is being produced against self

73
Q

What antibodies are used in the lab?

A

Anti-sera = antibodies produced in animals - a mixture (cheap)

Monoclonal = antibodies are identical to each other and bind the exact same epitope

74
Q

How are anti-sera antibodies produced?
(5)

A

We take antigen A and vaccinate a rabbit using it

The animal produces different types of antibodies against it

We take antibodies from rabbit

Purify antibodies

We now have a polyclonal mixture of antibodies which can be used to detect Antigen A

75
Q

How do anti-immunoglobulin antibodies worj

A

Antibodies against antibodies

Human antibody injected into animal -> provokes an immune response as it is seen as an antigen

Antibodies produced can be used to detect antibody

76
Q

How is anti sera used?
(5)

A

ELISA test

Antigen bound to well

Human antibody (if present) binds to antigen

Anti human antibody is added and binds to antibody

Anti-human antibody is marked with a horse radish peroxidase which creates a colour

77
Q

What is a monoclonal antibody?

A

An artificially created antibody from a single cell clone - binds same epitope

78
Q

Who immortalised plasma cells?

A

Georges Kohler
Cesar Milstein

79
Q

How were plasma cells immortalised?

A

Plasma cell were fused with myeloma cell which resulted in immortal cell producing monoclonal antibodies

80
Q

Describe the process of making monoclonal antibodies

A

Inject animal with antigen (multiple epitopes)
Animal makes antibodies - for each epitope
Kill the animal and take its spleen
Take plasma cell of spleen making the antibody of interest
Immortalise plasma cells by fusing them with myeloma cells
Dilute wells until we have a single cell per well (you have created an eternal source of antibodies for a specific antigen)

81
Q

Explain the relationship between HGPRT and spleen plasma cells
(3)

A

Myeloma cells are engineered so that they are deficient in HGPRT

Without HGPRT the myeloma cells will die

The spleen plasma cells gain immortality by providing the myeloma cell with HGPRT

82
Q

What is HGPRT?

A

Hypoxanthine-guanine phosphoribosyl transferase

Enzyme involved in purine synthesis

2.1 Molecular Immunology (19 decks)

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