Antigen and antibodies, structure and interaction

Question 1

What is an antigenic epitope (determinant)?

Answer 1

A specific target on the antigen body, which an antibody molecule binds to
-some antigens can have multiple epitopes
-some epitopes are immunodominant

Question 2

What is a hapten?

Answer 2

A small chemical group, which when chemically conjugated to a large molecule (carrier protein) will alter its specificity creating a new epitope

Question 3

What is an adjuvant?

Answer 3

A substance which, when combined with a antigen, non-specifically enhances the immune response

Question 4

Describe the structure of immunoglobulin G (IgG)

Answer 4

-Single Y shaped unit
-Gamma heavy chain
-Valence 2 (combines to 2 different antigens)

Question 5

What is the function of immunoglobulin G (IgG)?

Answer 5

-Fixes complement
-Acts a an opsonin
-Neutralises toxins
-Main Ig in secondary immune response
-Main (blood) serum Ig
-Diffuses easily to extravascular tissue

Question 6

Describe the structure of immunoglobulin M (IgM)

Answer 6

-5 Y shaped units
-Valence 10
-Mu heavy chain
-Extra heavy chain domain (CH4)
-J chain

Question 7

What is the function of immunoglobulin M (IgM)?

Answer 7

-Agglutinates particulate antigen
-Fixes complement
-Main Ig in early immune response
-Important in bacteraemia
-Intravascular

Question 8

Describe the structure of immunoglobulin A (IgA)

Answer 8

-Valence 4
-Monomer / dimer in serum (species dependent)
-Dimer in mucosal secretions (all species)
-alpha heavy chain
-Dimer linked by J chain
-Dimer at mucosal surfaces has ‘secretory piece’ (provides protection from enzymatic degradation)

Question 9

What is the function of immunoglobulin A (IgA)?

Answer 9

-Mucosal immune defence
-Inhibits microbial attachment
-Neutralises toxins
-Weak opsonin

Question 10

Describe the structure of immunoglobulin D (IgD)

Answer 10

-1 Y shaped unit
-Valence 2
-delta heavy chain
-Found only on surface of immature B lymphocytes

Question 11

Describe the structure of immunoglobulin E (IgE)

Answer 11

-1 unit
-Valence 2
-epsilon heavy chain
-Extra domain CH4

Question 12

What is the function of immunoglobulin E (IgE)?

Answer 12

-Involved in parasite rejection
-Involved in allergy
-Low level in serum
-More in animals than man
-Most bound to tissue mast cells or blood basophils