Immunogen/antigen

Question 1

What is an antigen?

Answer 1

Any foreign molecule / agent that is able to stimulate an IR (w/ a cell / antibody).

Question 2

What is the difference between a hapten and an immunogen?

Answer 2

• Hapten: a sml molecule that requires a carrier molecule to be able to stimulate IR (i.e. by itself ≠ IR)
• Immunogen: any molecule that can stimulate and IR (=immunogenic)

Question 3

Penicillin is an example of a drug that is classified as a hapten. What must happen inside the body for this hapten to stimulate an IR?

Answer 3

needs to be coupled to a larger molecule => IR

Question 4

Name the four major classes of antigens? Which two are considered poorly immunogenic by themselves?

Answer 4

a) Polysaccharides, proteins, lipids, nucleic acids

b) lipids & nucleic acids are haptens

Question 5

Which part of an antigen interacts with the immune system?

Answer 5

Epitope (aka antigenic determinant)

Question 6

List the 4 principle requirements for immunogenicity and explain each with a sentence?

Answer 6

1. Foreigness: more dissimilar to self = inc. immunogenicity
2. Molecular size: inc. size = inc. immunogenicity
3. Chemical complexity: inc. complexity (of lrg molecules) = inc immunogenicity
4. Susceptibility to antigen presentation: Hi enzyme degradability in APC = inc. immunogenicity

Question 7

List three components of the immune system that can recognise epitopes?

Answer 7

Epitopes recognised by:

1. antibodies (= immunoglobulin, Ig)
2. T cells via T cell receptor
3. Surface immunmoglobulin on B cells

Question 8

What kind of antigens are recognised by T cells compared with B cells? (native vs. processed; types of epitopes; classes of antigen recognised).

Answer 8

• B cells recognise native antigen (new); Accessible, non/sequential; Protein, polysacc., lipid
• T cells recognise processed antigen; Internal linear peptide; Peptide

Question 9

Difference between a sequential epitope and a conformational epitope?

Answer 9

• Sequential (aka linear): a specific sequence along peptide is recognised
• Differential (aka discontinous): relies on 3D structure of molecule (non-sequential AA binding)

Question 10

What happens when the conformational epitope changes?

Answer 10

≠ can’t attach to Ig ≠ recognised = hidden epitope

Question 11

What is tolerance?*

Answer 11

determines whether an IR is stimulated when values are not w/in the range*

Question 12

What is an adjuvant?

Answer 12

a substance that can enhance IR to an antigen (when both are mixed)

Question 13

Name one advantage of cross reactivity? Could you explain this in a paragraph?

Answer 13

reduce toxicity of epitope in vaccines. By modifying toxin epitope (=toxoid)= neutralise toxicity = not harm patient and allow Ig to be made to the other antigens

Question 14

Name one disadvantage of cross reactivity? Could you explain this in a paragraph?

Answer 14

Autoimmune rxns due to anitgenic similarity.

E.g. Strep. pyogenes’ & heart have similar shaped antigens to each other.

Question 15

what’s cross reactivity?

Answer 15

slight modification in antigen that doesn’t affect antigen’s immunogenic nature