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29 Cards in this Set

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What is an Antigen (Ag)?
is anything foreign to the body
Autoantigen
a self Ag (autologous)BAD- autoimmune disease
Alloantigen
an antigenic difference within a speices (allogeneic)
e.g., kidney transplant
Xenoantigen
an antigenic difference between species (xenogeneic)
e.g., pig heart
Immunogenic
An antigen that causes an immune response
Haptens
small molecules that are antigenic but not immunogenic.
Need to be attached to a carrier to become immunogenic
Effectiveness of macromolecules as Ag
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
What makes a good Ag?
More foreign, bigger, more complex.
Th1
activate T cells, CMR
Th2
(Activate B cells, HMR)
role of genetics in antigen response
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.
Relatively high and low doses are usually not immunogenic
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.
Route plays a role in immune response
intermuscular is better to produce a response because generally stays around longer.
Proteins
best antigenic bio-organic molecule
multideterminate Ag
multiple sites on molecule that can be regognized by antibody
Epitope
-Area that is recognized on Ag
-T cell epitopes are on inside of Ag
-B cell epitopes are on outside of Ag
B cell epitopes
-external epitopes
-can be sequential or non-sequential (conformational)
For proteins, ~8 – 22 a.a. interact with Ab
T cell epitopes
– 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
For a given protein Ag, there can be _______ T and B cell epitopes
multiple
epitopes can be ________
overlapping
some epitopes are __________
immunodominant
immunodominant epitopes
ones best at stimulating immune response
Types of immunogenic molecules
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
T-independent (TI) Ags
-Response does not require T cells
-B cell response
-no memory cells
T dependent (TD) Ags (BEST)
-Response requires T cell help (cytokines); T cell stimulation provides best immune response because produces memory cells
Haptens need T cell help for immunogenicity
if you bind hapten to protein carrier you can get secondary immune memory response to both bound hapten and bound carrier
Specificity of the immune response
The immune system can recognize slight differences in an antigen
e.g., recognizes difference between o,m,p aminobenzene
Usually, immune system is very specific but ________ do occur because non-related molecules can share ______.
This can result in _______
Cross-reactions, epitopes,autoimmunity
Adjuvants
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