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Immunology > 4. Antibodies > Flashcards

4. Antibodies Flashcards

1
Q

Antibody

A

protein produced in response to a foreign molecule (antigen),
binds specifically to that antigen

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2
Q

Immunoglobulins

A

Class of proteins formed by antibodies

Soluble glycoproteins

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3
Q

What produces antibodies?

A

B Lymphocytes

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4
Q

Prevalence of antibodies

A

Each individual has >10^7 different antibodies

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5
Q

Secondary effector functions of antibodies

A

Complement activation
Opsonisation
Cell activation via specific antibody-binding receptors (Fc receptors)

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6
Q

Structure of antibodies

A

2 heavy chains
2 light chains
Chains held together by interchain disulphide bonds
Always symmetrical (H=H, L=L)

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7
Q

Fab regions on antibodies

A

Variable regions with antigen binding activity

Don’t form protein crystals

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8
Q

Fc region on antibodies

A

Constant region

Will form protein crystals

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9
Q

Hinge region of antibodies allows

A

Flexibility

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10
Q

Flexibility of antibody molecules allows 2 Fabs to be wide apart

A

Can bind to wide apart antigens

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11
Q

Light and heavy chains can be divided

A

Into variable and constant regions

Variable at head

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12
Q

Purpose of variable and constant regions

A

Variable: Bind to antigen
Constant: Biological activity e.g. activates complement

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13
Q

Complementarity Determining Regions (CDR’s)

A

Within variable domains in amino acid sequence
Align at end of variable domain
3 hypervariable regions

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14
Q

Antigen and antibody show great degree of complementarity

A

Many interactions over short distances

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15
Q

Epitope

A

Part of antigen that’s bound to antibody

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16
Q

Forces involved in antibody/ antigen binding

A

Non-covalent
Weak
Therefore, need many interactions

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17
Q

Antibody affinity

A

strength of the total noncovalent interactions between a single antigen binding site and a single epitope on the antigen

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18
Q

Antibody avidity

A

overall strength of multiple interactions between an antibody with multiple binding sites and a complex antigen with multiple epitopes.

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19
Q

What is a better measure of binding capacity in biological systems?

A

Antibody avidity

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20
Q

Antibody cross-reactivity

A

Antibody elicited in response to 1 antigen can sometimes recognise a different antigen of similar structure

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21
Q

Examples of antibody cross reactivity

A

vaccination with cowpox induces antibodies which are able to recognise smallpox
Antibodies made against antigens on common intestinal bacteria may cross-react with carbohydrates on RBCs

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22
Q

Different classes of antibodies

A

Differ in the constant regions of their heavy chains
Have subtly different functions
Some have different locations in body

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23
Q

All classes of antibody use

A

The same light chains

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24
Q

How many classes of antibody are there?

A 
5
IgG
IgA
IgM
IgE
IgD
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25
Q

Which classes of antibodies have subclasses?

A

IgA: 2
IgG: 4

26
Q

IgG Antibody heavy chain

A

Gamma heavy chain

27
Q

Which is the most abundant immunoglobulin?

A

IgG

28
Q

IgG Occurs as a monomer, but has 4 subclasses

A

Variability mainly located in hinge region and effector function domains

29
Q

How is IgG involved in passive immunity?

A

Actively transported across placenta to foetus

30
Q

Where is IgG found?

A

In blood

Can enter extracellular fluids as it is small

31
Q

What is IgG a major activator of?

A

Classical complement pathway

32
Q

How are the 4 subclasses of IgG labelled?

A

1-4 on relative abundance

1= most abundant

33
Q

Different subclasses of IgG

A

Have different FC receptors

Subtle differences in responses

34
Q

IgA antibody heavy chain

A

Alpha heavy chain

35
Q

What is the 2nd most abundant immunoglobulin?

A

IgA

36
Q

How can IgA occur?

A

As a monomer (blood)

As a dimer (secretions)

37
Q

What is the main role of IgA?

A

Major secretory immunoglobulin

Protects mucosal surfaces from pathogens

38
Q

How is secretory IgA formed?

A

Plasma cell secretes IgA
IgA binds to Poly-Ig receptor on surface of epithelial cells
Stimulates receptor mediated endocytosis
In vesicle, Poly-Ig receptor cleaved, but part bound to IgA stays stuck on as ‘secretory component’- helps prevent degradation of IgA

39
Q

IgM antibody heavy chain

A

Mu heavy chain

40
Q

Structure of IgM

A

Large pentameric molecule

5 monomers joined by J chain (10 x Fab)

41
Q

Where is IgM found?

A

Mainly confined to blood (80%)

42
Q

What is the 1st immunoglobulin synthesised after exposure to antigen?

A

IgM

43
Q

What compensates for the low binding affinity in IgM?

A

Multiple binding sites

44
Q

What can IgM activate?

A

Complement system

45
Q

IgD antibody heavy chain

A

Delta heavy chain

46
Q

What are serum concentrations of IgD?

A

Extremely low serum concentrations

47
Q

When in surface IgD expressed?

A

Early in B cell development

48
Q

What is IgD involved in?

A

B cell development and activation

49
Q

IgE antibody heavy chain

A

Epsilon heavy chain

50
Q

IgE presence

A

Present at extremely low levels

51
Q

When is IgE produced?

A

In response to parasitic infections and allergic responses

52
Q

What does IgE bind to?

A

High affinity Fc receptors of mast cells and basophils

Cross linking by antigen triggers mast cell activation and histamine release

53
Q

Both IgG and IgM are found

A

In blood

54
Q

Which immunoglobulin can be found in extracellular fluid?

A

IgG

55
Q

Dimeric IgA is found

A

In secretions across epithelia, inc. breast milk

56
Q

Which immunoglobulin is transferred via the placenta to the foetus?

A

Maternal IgG

57
Q

Consequences of antibody binding to antigen

A 
Neutralisation
Agglutination
Opsonisation
Complement activation
Bound by cells expressing Fc receptors e.g. phagocytes
58
Q

Antibody function in defence

A 
Targeting of ineffective organisms
Recruitment of effector mechanisms
Neutralisation of toxins
Removal of antigens
Passive immunity in newborns
59
Q

Antibody function in medicine

A

Levels used in diagnosis and monitoring
Pooled antibodies for passive therapy/ protection
Monoclonal antibodies for treatment of cancer

60
Q

Antibody function in laboratory science

A

Vast range of diagnostic and research applications

Immunology (9 decks)

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