Antigen Processing and Presentation Flashcards
What are the three interactions necessary for T cell activaiton?
TCR/antigen
CD4 or CD8 stabilization
CD28/BL7
If a T cell recognizes antigen, but doesn’t receive the costimulation, what happens to the T cells?
It undergoes anergy - it will become inactivated or die
After activation, in time the CD28 will transform to what protein? What does this cause?
CTLA-4
It will still bind BL7 on the APC, but instead of this resulting in activation of the T cell, it will cause inhibition of the T cell - this is a “brake” system for the cellular response
Why are dendrites considered the “profession” APCs?
Because they constitutively express both MHC class 2 and costimulators
Macrophages need to be activated by phagocytosis to express both
B cells constitutively express MHC 2, but needs to be activated by antigen binding to antibody before they express costimulatory molecules
Presentation on MHC class 1 molecules is through what pathway?
cytosolic pathway
What sort of antigen is presented on MHC 1?
endogenous antigen - can either be healthy host antigen or viral antigen
How are proteins degraded for presentation in the cell during the cytosolic pathway?
proteins are tagged with Ub
The Ub is recognized by the 19S “lid” on the proteosome, where the protein is then degraded
How does the constitutive proteasome becaomse the immunoproteosome? Is it more or less efficient than the regular proteasome?
When the cell is stimulated with IFN gamma or TNF alpha (like when the cell is infected)
it’s more efficient because it will load peptides on MHC 1 faster through association with the TAP protein
Where are the MHC 1 molecules synthesized?
RER
How do the peptides from the proteosome get into the RER where the MHC is?
THey bind to a heterodimer complex of TAP1 and TAP2 located in the RER membrane, which facilitates the passage of the peptides into the lumen where loading onto MHC can take place
TAP has an affinity for peptides of what size?
8-16 amino acids, but really likes 9 amino acids
What molecules does the final trimming of the peptides before presentation?
ERAAP (ER-associated aminopeptidase) in the lumen of the RER
How does the MHC form in the membrane of the RER?
- first you get expression of the alpha chain and insertion of it intot he RER membrane
- the alpha chain binds to calnexin, which stabilizes it temporarily untli the alpha chain is in the appropriate comformation to bind to the B2 microblogulin
- Then calnexin dissociates and the alpha chain binds the B2 microglobulin
- Tapasin brings in the TAP1 and TAP2 structures close to the MHC
What “antigens” will be presented MHC 1 when the cell has abberant DNA synthesis?
Defective ribosomal products (DRiPs)
Antigens are presented on MHC 2 through what pathway?
endocytic pathway
