Nature Of Antigens Flashcards
Describe an antigen
Foreign macromolecules
Structurally complex
Multivalent
Definition of antigenicity
The ability of a molecule to specifically interact with a B cell receptor
4 types of antigens
Proteins
Polysaccharide
Lipids
Nucleic acids
What’s an epitope?
Part of an antigen that interacts with the antibody
What are epitopes also known as?
Antigenic determinant
What antigen valence
Indicates how many different antibodies are bound by an antigen
3 types of epitopes
Linear epitopes
Conformational epitopes
Buried epitopes
What a linear epitope?
Primary structure of protein
Conformational epitopes?
They are non sequential epitopes
2 types of epitopes?
Hidden or new
What a hidden epitope?
It’s buried within a protein due to its folding
New epitope?
Epitope is generated following proteolysis
Eg: peanut allergen
Who created the existence of conformational epitopes?
Sela et al (1971)
What did sela et Al do?
Used lysosomes
Immunised rabbits
Tested for reactivity
What’s an immunogen
An antigen that can induce an immune response
What are the 2 ways to elicit an immune response
T cell dependant
T cell independent
3 types of immunogens
Soluble substances
Viral substances
Molecules on particulate samples
What is the effect of immunogen exposure
Plasma cell produce secreted antibodies
What’s clonal expansion theory?
Activation of specific B cell receptor
B cell clone divides
B cell differentiates to plasma cell or memory cell
3 factors that contribute to immunogenicity of antigens
Immunogen contribution
Administration of immunogen
Biological system contribution
Immunogen properties which contribute to its immunogenicity
5 Foreigness Size Chemical composition Physical form Degradability
Foriegness properties
Immune system normally distinguishes between foreign and Self.the more distantly related 2 species are, the greater the immunogenicity of a substance of exposure is
Properties of size of the immunogen
The larger the molecule is the more immunogenic it is
Properties of chemical composition
The more chemically complex the more immunogenic
Properties of degradability
Antigens easily phagocytosed are more immunogenic
2 biological systems that contibute to immunogenicity
- genetic factors
2. age
Properties of genetic factors
Depending on your genes, depends on your t and B cell receptor count
Age properties
Very young/very old have very diminished immune response
3 administration options that effect immunogenicity
1-dose
2-route
3-adjuvant usage
Properties of dose
Optimal dosage
Too little—>no response
Too high—>poss. Tolerant
Route properties
Generally:
Subcutaneous route
Route determines immune organs involved
Adjuvant properties
Substance when mixed with the antigen aids/enhances the immune response
However side effects
What are haptens?
When combined with others=production of antibodies
Free haptens cannot induce immune response
Hapten definition
A low molecular weight molecule that can be made immunogenic by conjugation to a suitable carrier
What are antigens also known as?
Known as Ag
