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29 Cards in this Set
- Front
- Back
What is an Antigen (Ag)?
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is anything foreign to the body
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Autoantigen
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a self Ag (autologous)BAD- autoimmune disease
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Alloantigen
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an antigenic difference within a speices (allogeneic)
e.g., kidney transplant |
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Xenoantigen
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an antigenic difference between species (xenogeneic)
e.g., pig heart |
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Immunogenic
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An antigen that causes an immune response
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Haptens
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small molecules that are antigenic but not immunogenic.
Need to be attached to a carrier to become immunogenic |
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Effectiveness of macromolecules as Ag
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Proteins are often the most potent immunogens (only thing that can stimulate a T cell, best at B cells)
Polysaccharides are second (can stimulate B cells) Lipids and nucleic acids are usually not immunogenic |
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What makes a good Ag?
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More foreign, bigger, more complex.
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Th1
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activate T cells, CMR
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Th2
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(Activate B cells, HMR)
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role of genetics in antigen response
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Genetics determines whether one will respond with T helper 1 response, activating T cells and inducing a cell mediated response or T helper 2 which activates B cells and induces a Ab response. In addition if one doesn’t have the MHC (HLA) for a particular Ag, it will not induce an immune response. Similary, if one is lacking a B cell receptor (BCR) or T cell receptor (TCR) to an Ag there will also be no response.
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Relatively high and low doses are usually not immunogenic
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low doses are thought by the immune system to not be significant to engage a response. High doses indicate to the immune system that it might be self because there is so much of it.
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Route plays a role in immune response
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intermuscular is better to produce a response because generally stays around longer.
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Proteins
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best antigenic bio-organic molecule
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multideterminate Ag
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multiple sites on molecule that can be regognized by antibody
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Epitope
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-Area that is recognized on Ag
-T cell epitopes are on inside of Ag -B cell epitopes are on outside of Ag |
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B cell epitopes
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-external epitopes
-can be sequential or non-sequential (conformational) For proteins, ~8 – 22 a.a. interact with Ab |
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T cell epitopes
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– epitopes can be anywhere in protein
-are sequential -Between 8-10 a.a (CD8+) and 13-18 a.a. (CD4+) constraints by MHC binding groove Ag must interact with TCR AND MHC Ag must “fit” in binding groove of the MHC |
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For a given protein Ag, there can be _______ T and B cell epitopes
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multiple
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epitopes can be ________
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overlapping
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some epitopes are __________
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immunodominant
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immunodominant epitopes
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ones best at stimulating immune response
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Types of immunogenic molecules
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Starts a non-antigen specific activator of T or B cells which causes proliferation and then death
e.g. LPS non-specifically activates B cells so that they die out prematurely Concanavalin A (ConA) non-specifically activates T cells so that they die out prematurely |
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T-independent (TI) Ags
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-Response does not require T cells
-B cell response -no memory cells |
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T dependent (TD) Ags (BEST)
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-Response requires T cell help (cytokines); T cell stimulation provides best immune response because produces memory cells
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Haptens need T cell help for immunogenicity
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if you bind hapten to protein carrier you can get secondary immune memory response to both bound hapten and bound carrier
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Specificity of the immune response
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The immune system can recognize slight differences in an antigen
e.g., recognizes difference between o,m,p aminobenzene |
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Usually, immune system is very specific but ________ do occur because non-related molecules can share ______.
This can result in _______ |
Cross-reactions, epitopes,autoimmunity
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Adjuvants
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Adjuvants are compounds that when mixed with immunogens, makes them more immunogenic
equals stronger immune response e.g., oils or oil bases that make antigen stay around longer |