MHC and antigen presentation Flashcards
How do T cells function?
By making contact with other cells and inducing them to change
What part of the MHC molecule does CD8 bind?
alpha 3 domain of MHC class I
What part of the MHC molecule does CD4 bind?
beta 2 domain of MHC class II
How are peptide bound in the MHC peptide groove?
Hydrogen bonds and ionic interactions
What type of groove does type I have?
Groove closed - peptides bound in pockets at ends of groove
What type of groove does type II have?
Groove open - peptides bound along their length
What do peptides bound to MHC class I have?
Conserved anchor residues at ends - specific for each MHC isoform
Peptides for MHC class II come from what type of source?
Extracellular antigen
Peptides for MHC class I come from what type of course?
Intracellular antigen
Where are cytosolic proteins degraded?
Proteasome
What alters proteosome structure?
Infection (induced by IFNgamma) - constitutive proteasome into immunoproteasome
What happens to cytosolic proteins after they’re degraded?
Transported into ER via TAP
What stabilises MHC class I before beta2-microglobulin binds?
Calnexin
What does the peptide loading complex consist of?
Class I heavy chain, beta2-microglobulin, calreticulin, rapasin, TAP and ERp57
What is the role of tapasin?
Positions MHC class I to receive peptides and keeps the binding pocked in an open conformation
What is peptide editing?
When peptides are trimmed by aminopeptidases (ERAP) to ensure a good fit
What blocks the binding of peptides to class II molecules in the ER
Invariant chain
What happens to the invariant chain in vesicles?
Cleaved - leaving CLIP fragment bound which blocks peptide binding to class II in vesicles
What facilitates the release of CLIP and allows peptides to bind?
HLA-DM
What is cross presentation?
Done by class I molecules - rare event seen in viral infection where macrophages phagocytose infected cells
What type of cells are you most likely to find class I
Nucleated cells
What type of cells are you most likely to find class II
APCs
What influences the expression levels of MHC
Cytokines
Where is the variation in MHC allotypes concentrated?
At antigen binding sites
What represents selective pressure for MHC diversity?
Infectious diseases
How are new MHC alleles generated?
Interallelic conversion between same/ different genes
