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Antigen-antibody

HND Immunology

QuestionAnswer
What are the constituent parts of an antigen? Epitope and carrier.
What part of the antigen does the immune system recognise? The epitope only.
What name is given to an epitope isolated from an antigen? Hapten.
Are haptens immunogenic or antigenic? Antigenic, not immunogenic as they are too small.
How are haptens used during vaccinations? Hapten is attached to carrier (non-immungenic carriers are preferable) immune cells and antibodies react with hapten alone, developing an immunity for the substance with certain epitope.
What are the two common carrier molecules used with haptens? Keyhole Limpet Hemocyanin (KLH). Bovine Serum Albumin (BSA).
Describe KLH. A large complex protein derived from shellfish making it large and foreign. Has a high molecular weight of 5000kD with lots of attachment sites fo peptide coupling which makes conjugation easy.
What is one downside of KLH? It is poorly soluble in water which restricts its practical applications.
Describe BSA. A plasma protein in cattle with a molecular weight of 67kD and is more soluble than KLH.
Name a downside to BSA regarding immunoassays. If an antibody used in the immunoassay was raised using a heptin and BSA complex then a false positive results may be recorded which could lead to a disease being incorrectly diagnosed.
What are multiple antigenic peptides? An immunogen composed of multiple copies of a single hapten attached to a polylysine core that provides a scaffolding, meaning that heptins can be synthesised directly onto the branching arms.
Can multiple antigenic peptides be immunogenic? Yes as it is a big enough molecule.
What % of the total weight of MAP can heptins account for? 95%.
Where do epitopes recognised by B cells lie? On the surface of the antigen.
Where do epitopes recognised by T cells lie? Inside the antigen, and so can only be accessed once the antigen has been processed. T cells do not recognise native antigens.
Describe B cell epitopes. Lie on the surface of the antigen they are composed of hydrophilic peptides and have a high degree of flexibility, may be continuous or discontinuous epitopes.
What is the assortment of amino acids in a continuous epitope? The amino acids lie together in both the primary and tertiary structure of the protein.
What is the assortment of amino acids in a discontinuous chain? The amino acids lie together in the tertiary structure but not the primary structure.
Describe T cell epitopes. The epitopes are found on the inside of the antigen tertiary structure, they are hydrophobic and tend to be continuous amino acid sequences.
What type of bonds bind antigens and antibodies? Hydrogen bonds. Electrostatic interactions (ionic bonds). Van der Waals forces. Hydrophobic interactions.
What is critically important to the strength of the bonds between antigens and antibodies? The distance between interacting groups.
Why are weak bonds able to produce strong binding? The large number of bonds created.
How is the correct conformational shape produced by an antibody? and what effect does this have? Using other amino acids in the antibody structure. This allows a close fit between the antigen and antibody.
What is antibody affinity? The strength of the bond between antibodies and antigens.
What determines antibody affinity? The sum of all non-covalent bonds between the antigen and antibody.
Is antibody binding specific? No, antibodies can bind several epitopes with different affinities.
What is meant by specificity? The ability of an individual antibody binding site to react with one epitope.
What epitope features can antibodies often distinguish? The primary structure. Secondary and tertiary structures. Isomeric forms.
What is meant by cross reactivity? The ability of an individual antibody binding site to react with more than one epitope.
How do cross reactions arise? Because the antigen has an epitope which is structurally similar to one found on another antigen.
Can the same epitope exist on more than one specific antigen? Yes, epitopes can be on the same or different antigens.
Why is specific affinity more complex in the natural situation than on paper? It is only the strength of the binding between an individual antibody binding site and a corresponding single epitope, so only measures the binding of an antibody with a simple antigen containing a single epitope. In real life, antigens have >1 epitope.
Created by: MushetJ