Antigens

Question 1

What is an epitope?

Answer 1

• an antigenic determinant or ligand
• Defines a short sequence of amino acids or sugars in an antigen molecule that binds to a hypervariable region on an antibody
• Usually repeats several times. Number of repeats is called valence
• a microorganism may produce multiple epitopes

Question 2

What is valence?

Answer 2

The number of times a specific sequence of amino acids repeats on an epitope

Question 3

What is a hapten?

Answer 3

• The portion of the antigen molecule that contains the epitope
• Reacts specifically with an antibody
• can not induce antibody synthesis without a carrier molecule

Question 4

What is a super antigen?

Answer 4

• Can link multiple T cells to the MHC of an APC via T cell regions independent of their specific peptide binding sites
• associated with certain retroviral proteins and bacterial toxins
• activates many nonspecific T cells and APCs, causing secretion of extraordinary amounts of cytokine

Question 5

Factors that determine antigenicity:

Answer 5

1) degree of foreignness and host background
2) size, shape, chemical composition, amount, route, frequency of exposure
3) protein or polysaccharide vs lipid (poorly antigenic)

Question 6

What is antigen affinity?

Answer 6

The binding energy between an antibody and a univalent epitope

Question 7

What is avidity?

Answer 7

The total binding energy between an antibody and a multivalent antigen