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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
Which classes of antibodies have subclasses?
IgA: 2 IgG: 4
26
IgG Antibody heavy chain
Gamma heavy chain
27
Which is the most abundant immunoglobulin?
IgG
28
IgG Occurs as a monomer, but has 4 subclasses
Variability mainly located in hinge region and effector function domains
29
How is IgG involved in passive immunity?
Actively transported across placenta to foetus
30
Where is IgG found?
In blood | Can enter extracellular fluids as it is small
31
What is IgG a major activator of?
Classical complement pathway
32
How are the 4 subclasses of IgG labelled?
1-4 on relative abundance | 1= most abundant
33
Different subclasses of IgG
Have different FC receptors | Subtle differences in responses
34
IgA antibody heavy chain
Alpha heavy chain
35
What is the 2nd most abundant immunoglobulin?
IgA
36
How can IgA occur?
As a monomer (blood) | As a dimer (secretions)
37
What is the main role of IgA?
Major secretory immunoglobulin | Protects mucosal surfaces from pathogens
38
How is secretory IgA formed?
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
IgM antibody heavy chain
Mu heavy chain
40
Structure of IgM
Large pentameric molecule | 5 monomers joined by J chain (10 x Fab)
41
Where is IgM found?
Mainly confined to blood (80%)
42
What is the 1st immunoglobulin synthesised after exposure to antigen?
IgM
43
What compensates for the low binding affinity in IgM?
Multiple binding sites
44
What can IgM activate?
Complement system
45
IgD antibody heavy chain
Delta heavy chain
46
What are serum concentrations of IgD?
Extremely low serum concentrations
47
When in surface IgD expressed?
Early in B cell development
48
What is IgD involved in?
B cell development and activation
49
IgE antibody heavy chain
Epsilon heavy chain
50
IgE presence
Present at extremely low levels
51
When is IgE produced?
In response to parasitic infections and allergic responses
52
What does IgE bind to?
High affinity Fc receptors of mast cells and basophils | Cross linking by antigen triggers mast cell activation and histamine release
53
Both IgG and IgM are found
In blood
54
Which immunoglobulin can be found in extracellular fluid?
IgG
55
Dimeric IgA is found
In secretions across epithelia, inc. breast milk
56
Which immunoglobulin is transferred via the placenta to the foetus?
Maternal IgG
57
Consequences of antibody binding to antigen
``` Neutralisation Agglutination Opsonisation Complement activation Bound by cells expressing Fc receptors e.g. phagocytes ```
58
Antibody function in defence
``` Targeting of ineffective organisms Recruitment of effector mechanisms Neutralisation of toxins Removal of antigens Passive immunity in newborns ```
59
Antibody function in medicine
Levels used in diagnosis and monitoring Pooled antibodies for passive therapy/ protection Monoclonal antibodies for treatment of cancer
60
Antibody function in laboratory science
Vast range of diagnostic and research applications

Immunology (9 decks)

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