Lecture 9: MHC and Antigen Presentation Flashcards
term for the generation of peptides from proteins
antigen processing
what is antigen presentation
display of processed peptide on cell surface via a MHC molecule
what are the 3 types of professional APCs
- DC
- Macrophages
- B cells
*carry both MHC class I and II
is antigen presentation exclusive to APCs
no
cytosolic pathogens
viruses and some bacteria replicate in host cell cytosol
intravesicular pathogens
some bacteria can survive and replicate inside of the phagosome
extracellular pathogens
bacteria growing outside cell wall, virus not yet in a target cell
what do dendritic cells activate
Naive T cells
DCs sample their environment using ?
Toll like receptors
MHC molecules only bind _____ peptides
linear
what type of peptides do MHC Class I molecules bind? What are they displayed to?
endogenous peptides
displays them to CD8+ T cells
what type of peptides do MHC Class II molecules bind? What are they displayed to?
exogenous peptides
displays them to CD4+ T cells
what class of MHC is expressed by all nucleated cells
Class I
What class of MHC is expressed only by PAPCs
Class II
in what part of the cell do peptides bind MHC class I
in the ER
what is the role of proteasome?
breaks protein chain into small peptides and releases into cytoplasm (proteolysis)
INF-y increased the rate of proteolysis
what is the role of transporter proteins (TAP)
carry peptides of 8-16 amino acids into the ER
what is the role of ERAAP
further degrades peptide fragments to ensure they can fit into binding cleft
how can viruses evade antigen presentation
through the production of proteins called immunoevasins
how do immunoevasins
work
- block TAP function
- block antigenic peptide loading into MHC
- can tag MHC molecules for degradation by proteosome
what do intravesicular proteases do
degrade proteins
where do MHC Class II molecules form and fold
in the ER, then bud off and merge w/ antigen containing vesicle
what is the role of an invariant chain
it forms a complex w/ MHC class II, blocking the binding of peptides and misfolded proteins
what is the role of HLA-DM
similar to MHC II
- catalyzes the loading of antigen into MHC II binding pocket
- found only in MHC class II compartment
what is cross-presentation
occurs when DCs present antigens on their MHC I molecules that were not generated in their own cytosol
- rather, they were extracellular pathogens that were processed and displayed on MHC Class I
**critical for the activation of naive CD8 T cells
how do MHCs bind to so many antigens
genetic diversity
what does it mean that MHC molecules are co-dominantly expressed
both parental alleles of each MHC gene are expressed
what is an HLA haplotype?
the set of MHC alleles (class I and II) present on each chromosome
each animal has 2 HLA haplotypes (one from mom/dad)
what is the result of each MHC allele being polymorphic and polygenic?
each animal expresses a unique combination of MHC molecules
why are animals w/ MHC heterozygous alleles at an advantage to MHC homozygous alleles?
MHC heterozygous can respond to a greater range of antigens and therefore are best fit to survive infectious disease
MHC Class I Loci is encoded by….
HLA-A, -B, -C
MHC Class II Loci is encoded by….
HLA-DP, -DQ, -DR
polymorphic MHC means?
multiple alleles for each gene
give 2 examples of the expression of certain MHC alleles and disease susceptibility
Canine rheumatoid arthritis, I-M hemolytic anemia diabetes Mellitus
expression of certain BoLA alleles and resistance to bovine leukosis
what are superantigens
toxins (either bacterial or viral) that encourage unusual binding of TCR and MHC Class II molecules
binding becomes long-lived and produces a cytokine ‘storm’
what does it mean that MHC molecules have broad specificity?
many different peptides can bind to the same MHC molecule
however each MHC molecule displays one peptide at a time
what class of MHC do cytosolic peptides bind to
MHC class I
what class of MHC do intravesicular pathogens bind to
MHC class II
what class of MHC do extracellular pathogens and toxins bind to
MHC class II
