Antigens Flashcards
What are antigens able to bind to?
TCRs, MHC molecules, and antibodies
Define antigen.
Any molecule that cna induce an immune reposeone when introduced to the body
Define immunogen.
Any substance cabale of sitmulating an immune response
Define hapten.
Any substance that is unable to stimulate an immune response, until it’s bound to a larger molecule
Define immunogenicity.
The ability of a substance to induce cellular and humoral immune response
Define antigenicity.
The ability to be specifically recognized by the products generated as a result of the immune response to the given substance
Define epitope (antigenic determinant).
The part of the antigen that is responsible for inducing an immune reponse by binding to an MHC molecule, TCR, or antibody.
What two groups are associated with bacterial antigens?
- Soluble antigens: soluble substances produced and secreted by the bacterium
- Cellular antigens: structural units of bacterial cell
These can include:
- Somatic (O) antigen - Gram Neg and LPS
- Capsular (K) antigen - Capsule and its polysacch.
- Flagellar (H) antigen - Flagellin
- Fimbraial (F) antigen - Pili and frimbriae
- Spore antigen - exosporidium
What are examples of viral antigens?
Structural (envelope, nucleocapsid) and non-structural (viral proteins) antigens
What are examples of fungal antigens?
Chalmydoconidia, hypha, blastoconidia
What is an example of the challenges that antigens can cause?
Different antigens can be produced at different times in a period, and only present for a specific amount of time
True or False: In general, the antigenicity of a substance is related to the degree of its foreignness, as antigens from related species are less antigenic than those from unrelated (distinct) species.
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True
True or False: In general, the larger the molecular weight, the better are their antigenic properties, for example, penicillin and aspirin are not good antigens since their molecular weight is less than 1000 dalton.
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True
True or False: Large repeating polymers such as the lipids, carbohydrates and nucleic acids, are better antigens then complex carbohydrates.
False, the more complex of the arrangement of a foreign molecule, the more immunogenic it is
True or False: Highly flexible molecules that have no fixed shape are better antigens, rather than those that have a fixed shape when they bind to immune cells.
False, the more fixed in structure an antigen is, the more immunogenic it will be
Which of the following has the highest immunogenicity?
A) Polysaccharides
B) Nucleic acids
C) Lipids
A) Polysaccharides
Both lipids and NA’s are weakly antigenic, if at all
Which of the following would lead to a non-responsive state following the administration of antigens?
A) An insufficient dose
B) An excessive dose
C) Both A and B
D) None of the above
C) Both A and B
In an insufficient dose, it fails to activate enough lymphocytes resulting in a non-responsive state; whereas with an excessive dose, it causes lymphocytes to enter a non responsive state due to over stimulation.
How do adjuvants alter the immune system and its response to administered antigens, to increase its immunogenicity?
- Prolong antigenic persistence
- Enhance co-stimulatory signal
- Induce granuloma formation
- Stimulate lymphocyte proliferation non specifically
What types of antigen can be described as follows:
Complex antigens such as RBC, serum proteins etc. They are rapidly metabolized, require T cell help and produce memory and class switching.
T-dependent antigens
What type of antigen can be described as follows:
LPS of E coli, pneumococcal polysaccharide, flagellin, Lectin, Con A PHA, Pokeweed mitogen, etc., composed of repeating units. They are slowly metabolized, no memory or class switching.
T-independent antigens
T-independent antigens have __________ motifs throughout the length of the antigen, i.e. a polymeric structure.
Repeating
T-independent antigens can activate lymphocytes polyclonally. What does this mean?
They can bind to various B cells with different antigenic specificities to activate them
How resistant are T-independent antigens to degradation?
Very, due to their lack in ability to degrade which allows them to be sustained longer
Proteins are considered the largest group of antigens, and are predominantly T-__________ antigens. They can be quickly degraded and require T helper cells for stimulation.
Dependent
Streptococcal A antigen is a bacterial antigen that does not need to processed by professional antigen presenting cells in order to activate T cells. How would you describe this antigen?
A) Heterophile antigen
B) Autoantigen
C) Superantigen
D) Allantigen
C) Superantigen
Heterophile antigens are antigens of identical nature present in the cells of some bacterial species and also in the tissues of different animals
Autoantigens are antigens from your own body tissues, that develop antigenic properties and antibodies formed against those antigens
Allantigens are antigens present in one individual, and are antigenic to some other individuals of the same species.
Derived from bacteria and viruses, describe how superantigens illicit an immune response.
They bind to the varibale domain of the beta chain in TCR’s and the alpha chain of the MHC II receptors on APC’s, which will activate T cells polyclonally
Following polyclonal activation of T cells form superantigens, what cytokines will be produced excessively?
IL-1, IL-2, IL-6, TNFalpha, MIP-1 alpha, and MIP-1 beta
What broad term can be applied to any type of antigen that enters the body from an outside source due to inhalation, ingestion, infection, etc.?
Exogenous antigens
What broad term can be applied to antigens that are generated intracellularly as a result of normal cellular metabolism, including viral and bacterial caused infections?
Endogenous antigens
