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57 Cards in this Set

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  • Back
What is the most important distinction between class I and II antigen presentation?
The source of peptides
What samples the cytoplasm of cells?
Class I
What samples the extracellular areas?
5 things that must happen for Class I antigen presentation:
1. Tag proteins
2. Proteolysis
3. Delivery of peptides to MHC I
4. Binding of peptide to MHC I
5. Display of Ag/MHC to T cell
What tag is used to target intracellular proteins for degradation?
What residue does Ubiquitin bind?
What degrades peptides after polyubiquitination?
A proteosome
What is an immunoproteosome?
A proteosome that has had 3 beta subunits in its core replaced with LMP's encoded in MHC
What stimulates the replacement that makes an immunoproteosome?
IFN-y produced from NK cells and T cells during viral infections
Do proteosomes only degrade antigenic material?
No - every single protein in the cell is subject to turnover.
How big is the diameter of the center of a proteosome?
13 angstroms
What has to happen to proteins before they can be degraded by the proteosome core?
After the CAP recognizes the poly-Ub tag, it must be removed by isopeptidases
What size of residues are generated by the proteosome?
4-20 AA long
What size peptides does MHC I fit?
8-10 AA long
Where in cells are proteasomes located?
In the cytoplasm
Where is Class I MHC made?
In the ER
So how do proteins degraded in the cytosolic proteasome get in contact with Class I MHC in ER?
Via TAP transporter
What does putting peptides into the ER with TAP allow?
Stable uniting of the MHC heavy chain with B2m and peptide.
Where is TAP encoded?
Within MHC
What type of protein substrates does TAP select for?
Those ending in LIVM, and 6-15 residues long
What molecules link TAP to MHC I and aid during transfer of the peptide in the ER?
Tapasin - links TAP to MHC I
Calreticulin/Calnexin - chaperones that aid too.
Does MHC I only present foreign antigenic peptides on its surface?
OF COURSE NOT! It presents self peptides all the time, on healthy cells.
If self antigen is being presented on MHC I to Tc cells all the time, how come all nucleated cells don't die then?
Because Tcells that would react to self antigen are eliminated during thymic education.
What is alloreactivity?
The reaction of our own T and B cells to nucleated cells in transplanted tissue, which though it presents self Ag, uses foreign MHC to do it.
What length of peptides are presented by Class I MHC again?
8-10 residues
What length of peptides are presented by Class II MHC?
10-16 residues, but can be up to 30 residues!
What is the source of peptides presented by Class II MHC?
How do the extracellular proteins get into the cell?
By endocytosis
How are the endocytosed proteins degraded into peptides?
By lysosomal enzymes
What are the lysosomal proteases that chop up microbial proteins called?
What is required for Cathepsins to be active?
pH=5 within lysosome
Where is Class II MHC made?
In the ER
How come Class II MHC doesn't get loaded with peptides bound for Class I MHC?
-Peptides bound for Class I MHC are bound to TAP and need tapasin to link them together.
-Class II MHC is satisfied with invariant protein
What purpose does Invariant chain serve other than preventing peptide loading onto MHC II prematurely?
Its dileucine motif serves as a zipcode to sort MHC II to lysosomes rather than the default presentation pathway.
In what exact form does Class II MHC travel from the ER to lysosomes?
As a trimer composed of 3 MHCII molecules and 3 invariant chains.
Where does invarient chain contact MHC II?
it binds right in the binding cleft
What is the final state of invariant chain once MHCII gets to the lysosome?
It is cleaved and leaves a CLIP bound in the binding cleft.
What is responsible for exchanging antigenic peptide in place of CLIP on MHC II in lysosomes?
After CLIP is dislodged from MHC II's binding cleft, what does HLA-DM do?
Keeps bumping antigenic peptides out of the cleft until one fits so perfectly that it can't be jarred.
What happens to MHC II if a peptide doesn't bind well enough and HLA-DM keeps jarring them out of the groove?
Without peptide MHCII is unstable, it unfolds, and is destroyed by proteases in the lysosome.
Can self peptides be presented on MHC II to CD4 pos Thelper cells?
Can self peptides be presented on MHC I to CD8 pos Tcytotoxic cells?
uhhhh YES
What is Cross-presentation?
The presentation of extracellular peptides on MHCI
What cells are capable of cross presentation?
Only specialized APC's
Are MHCI and MHCII the only antigen presenting molecules?
NO; also CD1 can do it
What class of MHC does CD1 resemble most? Why?
Class I - it binds B2-microglobulin and has a similarly shaped groove.
What type of antigen is presented by CD1?
LIPID (not peptide)
Is CD1 encoded within MHC?
What cells possess CD1?
only APCs
What cells possess MHCII?
only APCs
What cells are capable of cross-presenting?
only APCs
What cells have MHC I?
All nucleated cells
What do APCs with CD1 present lipid TO?
CD1-specific T cells
How does CD1 travel when not lipid-bound?
With invariant chain
What are the 3 main types of specialized APCs?
1. B cells
2. Dendritic cells
3. Macrophages
What cells can be induced to become APCs?
Keratinocytes and some others
What induces keratinocytes to become APCs?