Lecture 7: Antigen Presentation and the MHC Flashcards
All nucleated cells express ______ ______ __ molecules and can present antigen via these molecues
MHC Class I
What are 2 methods in which antigen presenting cells can take up antigen?
1) surface receptors
2) phagocytosis
What are the 3 cell types where MHC Class II is expressed?
1) Macrophages
2) Dendritic cells
3) B lymphocytes
What are skin APCs called? Where do they present antigen?
Langerhan cells; T cells
What are the 2 lineages of Dendritic Cells?
1) Conventional
2) Plasmacytoid
What is the function of Plasmacytoid cells?
produce large quantities of interferon in response to viral infections
What are the macrophages in the brain?
microglial
True or false: B lymphocytes present only one type of antigen?
True (whatever binds to B cell receptor)
What is required for the actual presentation of antigens for MHC Class I?
cytosolic production of viral proteins
How do MHC Class II molecules pick up the ingested antigen?
vesicles containing MHC Class II fuse with the vesicle in which the antigen was phagocytosed
Antigenic peptides that bind to MHC Class I are typically derived from ________
viruses
In MHC Class I antigen presentation, peptides generated in the cytoplasm are transported into the ER by ________ and ________.
TAP 1 and TAP 2
transporters associated with antigen processing
Once in the ER, how does the antigenic peptide associate with MHC Class I molecules?
MHC Class I associates with TAP and as peptides are transported into the ER, they are trimmed by ERAAP (endoplasmic reticulum aminopeptidase associated with antigen processing) then bind to MHC Class I
As MHC Class I is being made in the ER, what do the alpha chains post up against while waiting for the beta 2 microglobulin to bind?
calnexin
Once the beta 2 chains associate with the alpha chains of the MHC, what keeps the molecule from unfolding?
binding to chaperone protiens (calreticulin, ERp57)
Which chaperone facilitates MHC Class I binding to TAP?
tapasin
When is the MHC Class I molecule released to the membrane?
Once it has bound to its peptide in the ER (after ERAAP cleaved the incoming antigen)
MHC Class I peptides are degraded in the ____________ while MHC Class II molecules are degraded in _____________.
cytosol (by the proteasome) and acidified endosomes
MHC Class II molecules are transported to endosomes with _____________ which occupies the peptide binding cleft of the newly synthesized MHC
invariant chain (Ii)
Once in the endosome, Ii is cleaved, leaving a short peptide fragment called _______
CLIP
class II associated invariant chain peptide
CLIP is only removed from the binding cleft when the endosome fuses with an phagocytized vesicle of antigen. Which protein unloads CLIP and loads the antigen?
DM
Under normal conditions, MHC Class I molecules are __________(loaded/unloaded) while MHC Class II are ___________
loaded (with self peptides derived from normal degradation)
unloaded (only have CLIP in binding groove)
Under normal conditions, MHC Class I molecules are __________(loaded/unloaded) while MHC Class II are ___________
loaded (with self peptides derived from normal degradation)
unloaded (only have CLIP in binding groove)
CD4 T lymphocytes do not recognize free/soluble antigens, they only recognize ________
MHC Class II bound
