4 - immunogens + antigens Flashcards
Define antigen
any molecule able to specifically interact with a component of the immune system
What are the type of antigens
Haptens
Immunogens
Define haptens
any molecule that can interact with the immune system but cannot stimulate an immune response by itself
Define an immunogen
any molecule that can stimulate an immune response
Provide examples of haptens
Prescribed medication: penicillin + hydralazine
Define hapten carrier molecules
Large immunogenic molecule to which a hapten/other non-immunogenic epitope molecule may attach to become immunogenic -> inducing an immune reponse
Provide examples of bacterial immunogens
- Streptococcus pyogenes: laemolysin O, Dnase B
- Listeria monocytogenes: Listeriolysin O
What are the major classes of antigens?
polysaccharides
proteins
lipids
nucleic acids
What are the requirements for immunogenicity
- foreignness
- molecular size
- chemical complexity
- susceptibility to antigen processing and presentation
immunogenicity: foreignness
self vs. non self
more foreign -> greater immunogenicity
immunogenicity: molecular size
- small molecules: low immunogenicity
- larger molecules: high immunogenicity
- most have size and complexity to be immunogenic
immunogenicity: chemical complexity
- increased structural complexity -> high immunogenicity
immunogenicity: susceptibility to antigen processing + presentation
- primarily protein molecules
- increased enzyme degradation = increased immunogenicity
- occurs inside an APC
Epitope
Small part of an antigen that is recognised by the immune system
Present on all antigens
What type of antigen does B cell recognise ?
Native antigen
What type of antigen does T cell recognise?
Processed antigen
Describe sequential epitopes
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
Describe conformational epitopes
discontinous epitopes
non sequential
created from aa residues located in different parts of poly peptide chain
What are the requirements for immunogenicity
- genetic makeup
- number of doses/times exposed to antigen
- Route of administration
Define adjuvant
substance when mixed with an antigen enhances an IR to that antigen
mechanism of action vaires according to adjuvant used
What adjuvant is considered toxic?
Aluminium hydroxide -> neurotoxin can cause encephalis in susceptible individuals
Describe the mechanism of cross reactivity
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
How are toxins modified to toxoid?
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
