MHC Flashcards
Class I structure
two polypeptide chains: the 𝛼 chain non-covalently associated with the β2-
- 3 different alpha domains
○ Alpha 2 and 1 bind to peptide
1 beta domain
Class I structure: genes
the 𝛼 chain encoded in the MHC on chromosome 6 in humans
β2-microglobulin (encoded on chromosome 15 in humans)
How big are the peptides bound on binding cleft of MHC I
closed, so short peptides of 8-10 amino acids
MHC class II structure
two noncovalently bonded chains
alpha and beta
binding cleft is open (13-17 amino acids)
Where are the alpha and beta genes for MHC II located
both encoded within the MHC gene region
What are anchor residues?
Anchor residues: set of peptides that can bind to a given MHC, and anchor to the MHC molecule to make it more stable
Different peptides can bind to the same MHC, but they need to have anchor residues with the same properties and around the same position
How are human MHC alleles named
HLA - name for human MHC
A/B/C (class I genes for alpha chain) or DR/DP/DQ (MHC class II alpha and beta genes)
number = allelic variation
Polygeny and polymorphism definitions
Polygeny = Means that there are several related genes relating to MHC
polymorphism = Different variations of the same gene
how does polygeny and polymorphism contribute to diversity
Polygeny: diversity means that we can respond to most pathogens
Polymorphism: pathogen can escape some of the alleles - diversity means that we don’t mount the same immune response
What is MHC restriction
For a T cell to recognise the MHC bound peptide, it needs to be specific to the antigen AND the MHC molecule - the allele of which it is trained to recognise in the thymus
alloreactive t cells
T cells react to non-self MHC molecules
- either from the foreign peptide bound
- or the MHC molecule alone
why are grafts between HLA-identical siblings rejected?
polymorphic proteins differ between donor and recipient which can be presented in MHC molecules
direct vs indirect allorecognition
indirect: dendritic cells process and present donor antigens to T cells
direct: T cells recognise foreign MHC on graft
