Immunology: Antigens

Question 1

Define antigen

Answer 1

Anything causing an immune response, usually foreign material but may be our own tissues (autoimmunity).

Question 2

Define hapten

Answer 2

A small chemical group that alone is non-immunogenic, but when attached to a larger carrier protein can act as an antigenic determinant and elicit antibody or cellular immune responses

Question 3

Define carrier

Answer 3

Foreign proteins to which small non-immunogenic molecules (haptens) can be coupled to stimulate an immune response. Self proteins can also serve as carriers e.g. allergy to drugs

Question 4

Define adjuvant

Answer 4

Any substance which, mixed with an antigen, enhances the immune response to that antigen

Question 5

What is antigenic variation?

Answer 5

Pathogen exists as multiple strains e.g. 84 serotypes of S. pneumoniae

Question 6

What is antigenic drift?

Answer 6

Point mutations in the DNA which lead to a coding change in the amino acid which in turn results in a small change in the structure of the protein:No antibodies recognise drifted epitope, therefore immune response is partially but not fully protective

Reassortment of genome segments = Two virus strains circulating in the same host
• Major variation in protein
• No antibodies recognise shifted protein
• Therefore immune response is not protective

Question 7

What is antigenic shift?

Answer 7

Reassortment of segments in the genome between different strains of the same pathogen, leading to dramatic changes in the expressed protein. The change is so radical that the protein(s) is no longer recognised by the immune response, causing serious disease outbreaks

Question 8

What are the consequences of drift, variation and shift?

Answer 8

Variation: leads to multiple (consecutive) infections with the same pathogen
Drift: mild epidemic occurs as degree of cross protection still exists
Shift: pandemic occurs as population has no immunity
Difficulties for health / vaccine design