LW - Antigens and antibodies, structure and interaction

Question 1

What is the definition of an antigen?

Answer 1

A substance which binds to a lymphocyte receptor and in doing so may initiate an immune response.

Question 2

What is an autoantigen?

Answer 2

Antigens part of the normal body.

Question 3

What is an alloantigen?

Answer 3

Cells from the same species but genetically different.

Question 4

What is a xenoantigen?

Answer 4

Cells from different species.

Question 5

Why can one substance be more antigenic than another?

Answer 5

• 1 antigen may have several epitopes.

- 1 of which could be immunodominant.

Question 6

What is an epitope?

Answer 6

A part of the antigen that causes an immune response.

Question 7

What is a hapten?

Answer 7

A small chemical group, which when chemically conjugates to a larger protein will alter its specificity creating a new epitope.

Question 8

What is an immunogen?

Answer 8

A substance that induces and immune response when injected into an individual.

Question 9

What factors determine immunogenicity?

Answer 9

• Method of preparing the antigen.
• Species and strain of the recipient.
• Dose of antigen.
• Route of administration.
• Use of adjuvant.

Question 10

What is an adjuvant?

Answer 10

A substance, which when combined with an antigen, non-specifically enhances the immune response.
May also cause slow release of an antigen

Question 11

What are the 5 classes of immunoglobulin?

Answer 11

IgA, IgE, IgM, IgD, IgG

Question 12

Describe the structure of IgG.

Answer 12

Single y-shaped unit.
Valence = 2
Gamma heavy chain.

Question 13

What is the function of IgG?

Answer 13

Main Ig found in the body. 
Diffuses easily. 
Neutralises toxins. 
Main Ig in a secondary immune response. 
Fixes complement. 
Enhances phagocytosis.

Question 14

Describe the structure of IgM.

Answer 14

5 y-shaped units. 
Valence = 10
Mui heavy chain.
Extra heavy chain - CH4.
J chain helps to link all of the units

Question 15

What is the function of IgM?

Answer 15

Agglutinates particulate antigen.
Fixes the complement.
Main Ig in the early immune response.
Intravascular - stays in the blood.
Important in bacteraemia.

Question 16

Describe the structure of IgA.

Answer 16

Can exist as a monomer or a dimer - dimer in mucosal secretions.
Dimer is linked by J chains. And at the mucosal surface has a ‘secretory piece’, this provides protection from enzymatic degradation.
Valence = 2/4
alpha heavy chain

Question 17

What is the function of IgA?

Answer 17

Mucosal immune defence.
Inhibits microbial attachments.
Neutralises toxins.
Weak opsonin.
There are further subclasses.

Question 18

What does opsonin mean?

Answer 18

An antibody or other substance which binds to foreign microorganisms or cells making them more susceptible to phagocytosis.

Question 19

Describe the structure of IgD.

Answer 19

1 y-shaped unit.
Valence = 2
Delta heavy chain.

Question 20

What is the function of IgD?

Answer 20

• Found on the surface of immature B-cells.

- No clear function.

Question 21

Describe the structure of IgE.

Answer 21

1 y-shaped unit.
Valence = 2
Epsilon heavy chain.

Question 22

What is the function of IgE?

Answer 22

• Low level in serum.
• Mostly bound to mast cells of blood basophils.
• Parasite rejection and allergies.

Question 23

What determines antibody affinity?

Answer 23

The attractive force between the antigen and the antibody.

Question 24

What is antibody avidity?

Answer 24

The measure of the total binding strength of an antibody. Taking into account each binding site.

Question 25

Describe how an antigenic epitope binds to an antibody.

Answer 25

The antigenic epitope slots into a groove formed between the hyper variable regions of the heavy and light chains.

Question 26

After pepsin acts on an antibody, which regions are left?

Answer 26

1 x Fab’2

1 x Fc

Question 27

After papain acts on an antibody, which regions are left?

Answer 27

1 x Fc

2 x Fab