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Anti/Immunogenicity
HND Immunology
Question | Answer |
---|---|
Define the term antigenicity. | The ability of a substance to react with specific antibodies or T cells. |
What must an antigen be in order to elicit an immune response? | Sufficiently unique and recognisable. |
What are the unique molecular structures found on antigens that allows binding to immune cells called? | Epitopes. Which each one eliciting a separate response. |
How many epitopes can antigens contain? | Antigens may contain several of the same or differing epitopes. With each attaching to a different antibody or surface receptor. |
What are epitopes made up of? | 5-15 amino acids for protein antigens. 3-6 sugar residues for carbohydrate antigens. |
What are the 3 protein classes that can function as an antigen? | Glycoproteins. Lipoproteins. Nucleoproteins. |
What is the polysaccharide group that can function as an antigen? | Lipopolysaccharides. |
Will lipids or nucleotides generally act as antigens? | Not unless attached to a protein group. |
What infectious material carries antigens? | Viruses. Bacteria. Fungi. Protozoa. Bacterial toxin. |
What non-infectious material carries antigens? | Dust, hair, pollen (allergens). Foreign tissue. Cancer cells. |
Define the term immunogenicity. | The ability of a substance to elicit an immune response. |
What is an immunogen? | A substance that elicits an immune response. |
What is an antigen? | A substance that binds to an antibody or immune cell. |
Are all antigens immunogens? | No, as not all antigen induce an immune response. |
Are all immunogens antigens? | Yes, as the immunogen must bind to a cell or antibody to induce the immune response. |
What 4 features must be present in a substance for it to be classed as an immunogen? | It must have; a high molecular weight, a varied chemical composition, a degree of degradability and show foreignness to the host. |
Describe what is meant by "immunogenic substances must have a high molecular weight". | Only macro-molecules (>5kD) are immunogenic, the larger the molecule the more immunogenic it is. The building blocks of macro-molecules can be antigenic, but not immunogenic. |
What is meant by "immunogenic substances must have a varied chemical composition"? | For macro-molecules to be immunogenic they must have chemical complexity, i.e. homoploymers such as glycogen are not immunogenic as they don't have distinguishing features, but heteropolymers such as globular proteins are due to amino acid diversity. |
What is meant by "immunogenic substances must have a degree of degradability"? | Immunogenic antigens must be able to be broken down inside the cells so that its epitopes can be displayed on B cells and other antigen presenting cells. |
What is meant by "immuogenic substances must show foreignness to the host"? | Immunogens must have a structure that is foreign to the host, This is done by HLA antigens on the surface of host cells which can be recognised as part of the hosts body. Any antigen not containing the same marker can be recognised as foreign. |
What differs about how B cells and T cells bind to epitopes? | B cells bind directly to the epitope while T cells only bind to epitope and MHC-II complex. |
What are the two constituent parts of an antigen? | The epitope and the carrier. |
What name is given to an epitope that is isolated from its carrier? | Hapten. |
Are haptens antigenic, immunogenic, or both? | Antigenic, not immunogenic. |
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. |