HND Immunology
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| What are the constituent parts of an antigen? | Epitope and carrier.
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| What part of the antigen does the immune system recognise? | The epitope only.
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| What name is given to an epitope isolated from an antigen? | Hapten.
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| Are haptens immunogenic or antigenic? | Antigenic, not immunogenic as they are too small.
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| 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.
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| What are the two common carrier molecules used with haptens? | Keyhole Limpet Hemocyanin (KLH). Bovine Serum Albumin (BSA).
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| 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.
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| What is one downside of KLH? | It is poorly soluble in water which restricts its practical applications.
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| Describe BSA. | A plasma protein in cattle with a molecular weight of 67kD and is more soluble than KLH.
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| 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.
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| 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.
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| Can multiple antigenic peptides be immunogenic? | Yes as it is a big enough molecule.
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| What % of the total weight of MAP can heptins account for? | 95%.
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| Where do epitopes recognised by B cells lie? | On the surface of the antigen.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| What type of bonds bind antigens and antibodies? | Hydrogen bonds. Electrostatic interactions (ionic bonds). Van der Waals forces. Hydrophobic interactions.
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| What is critically important to the strength of the bonds between antigens and antibodies? | The distance between interacting groups.
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| Why are weak bonds able to produce strong binding? | The large number of bonds created.
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| 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.
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| What is antibody affinity? | The strength of the bond between antibodies and antigens.
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| What determines antibody affinity? | The sum of all non-covalent bonds between the antigen and antibody.
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| Is antibody binding specific? | No, antibodies can bind several epitopes with different affinities.
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| What is meant by specificity? | The ability of an individual antibody binding site to react with one epitope.
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| What epitope features can antibodies often distinguish? | The primary structure. Secondary and tertiary structures. Isomeric forms.
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| What is meant by cross reactivity? | The ability of an individual antibody binding site to react with more than one epitope.
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| How do cross reactions arise? | Because the antigen has an epitope which is structurally similar to one found on another antigen.
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| Can the same epitope exist on more than one specific antigen? | Yes, epitopes can be on the same or different antigens.
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| 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.
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