4 - immunogens + antigens

Question 1

Define antigen

Answer 1

any molecule able to specifically interact with a component of the immune system

Question 2

What are the type of antigens

Answer 2

Haptens

Immunogens

Question 3

Define haptens

Answer 3

any molecule that can interact with the immune system but cannot stimulate an immune response by itself

Question 4

Define an immunogen

Answer 4

any molecule that can stimulate an immune response

Question 5

Provide examples of haptens

Answer 5

Prescribed medication: penicillin + hydralazine

Question 6

Define hapten carrier molecules

Answer 6

Large immunogenic molecule to which a hapten/other non-immunogenic epitope molecule may attach to become immunogenic -> inducing an immune reponse

Question 7

Provide examples of bacterial immunogens

Answer 7

• Streptococcus pyogenes: laemolysin O, Dnase B

- Listeria monocytogenes: Listeriolysin O

Question 8

What are the major classes of antigens?

Answer 8

polysaccharides
proteins
lipids
nucleic acids

Question 9

What are the requirements for immunogenicity

Answer 9

1. foreignness
2. molecular size
3. chemical complexity
4. susceptibility to antigen processing and presentation

Question 10

immunogenicity: foreignness

Answer 10

self vs. non self

more foreign -> greater immunogenicity

Question 11

immunogenicity: molecular size

Answer 11

• small molecules: low immunogenicity
• larger molecules: high immunogenicity
• most have size and complexity to be immunogenic

Question 12

immunogenicity: chemical complexity

Answer 12

• increased structural complexity -> high immunogenicity

Question 13

immunogenicity: susceptibility to antigen processing + presentation

Answer 13

• primarily protein molecules
• increased enzyme degradation = increased immunogenicity
• occurs inside an APC

Question 14

Epitope

Answer 14

Small part of an antigen that is recognised by the immune system
Present on all antigens

Question 15

What type of antigen does B cell recognise ?

Answer 15

Native antigen

Question 16

What type of antigen does T cell recognise?

Answer 16

Processed antigen

Question 17

Describe sequential epitopes

Answer 17

linear epitopes
aa residues are adjacent in polypeptide chain
nucleic acid changes can lead to altered aa sequency, inhibiting antigen binding by aby T/B cells

Question 18

Describe conformational epitopes

Answer 18

discontinous epitopes
non sequential
created from aa residues located in different parts of poly peptide chain

Question 19

What are the requirements for immunogenicity

Answer 19

1. genetic makeup
2. number of doses/times exposed to antigen
3. Route of administration

Question 20

Define adjuvant

Answer 20

substance when mixed with an antigen enhances an IR to that antigen
mechanism of action vaires according to adjuvant used

Question 21

What adjuvant is considered toxic?

Answer 21

Aluminium hydroxide -> neurotoxin can cause encephalis in susceptible individuals

Question 22

Describe the mechanism of cross reactivity

Answer 22

occurs when there is a slight modification of an antigen epitope without altering immunogenic nature of the molecule
usually accomplished with large molecules with several antigen epitopes

Question 23

How are toxins modified to toxoid?

Answer 23

Epitope responsible for toxin function modified so toxoid does not cause disease in vaccine recipient
Antibodies made against the unmodified antigenic determinants of the toxoid can neutralise the real toxin during an infection