Final MHC Flashcards
What are and what do MHC molecules do?
- they display antigens to T cells
- cell surface glycoproteins
How many classes of MHC are there
3
What is special about MHC genes?
Polygenic, multiple genes for the class (1, 2, 3)
Which chromosome is the MHC gene complex for humans and mice?
- 6
- 17
Explain class 1 MHC?
- present altered self antigens or viruses to activate cytotoxic T cells
- found on nearly all nucleated cells of the body
- each gene encodes an alpha chain protein
Explain Class 2 MHC?
- present processed extracellular bacteria to helper T cells
- expressed only on membranes of antigen presenting cells (macrophage, dendritic cells, B cells)
- each region encodes both an alpha and beta chain
Within a population is there a lot or a bit of MHC diversity?
-a lot of diversity between species
For individuals, is there diversity in MHC?
No, all MHC molecules in individuals are the same
Where does the diversity for MHC come from?
Polymorphism, multiple alleles within the MHC gene loci
How many MHC 1 and 2 alleles do you inherit from mom and dad
- 3 MHC 1 from mom an 3 from dad
- 3 MHC 2 from mom and 3 from dad
How many MHC 1’s are expressed?
All 6 on a nucleated cell
How many MHC’s are expressed on APC’s?
12 MHC’s
Describe MHC 1 peptide bonding?
- can only hold a peptide of 8-10 amino acids
- anchor residues hold peptide in place
Describe MHC 2 peptide bonding
- can hold a peptide of 13-18 amino acids
- peptide is exposed and flat across the surface
- anchor points distributed across ends and centre of peptide
- interaction involves hydrophobic residues
What is antigen processing?
The degradation of antigens into peptides
What is antigen presentation?
Describes the binding of the peptide by MHC and displaying the peptide at the cell surface to interact with T cells
Where are MHC 1 antigens processed?
In the cytoplasm
Where are MHC 2 antigens processed?
In the endocytic pathway
What is the purpose of antigen processing?
To generate peptides that will fit in the MHC binding cleft
What are the steps of MHC 1 antigen processing?
- identification and cleavage of target proteins
- transport to endoplasmic reticulum
- loading onto MHC 1
- expression on cell surface
1, 2. Describe identification and cleavage of target proteins and the transport for MHC 1?
- proteins are degraded by proteasomes
- peptides are then transported from the cytoplasm to the endoplasmic reticulum by the transporter of antigenic peptides (TAP)
3, 4. Describe the loading and expression of MHC 1?
- peptides are loaded onto pre-formed MHC 1
- stabilized by chaperone proteins
- once a peptide is loaded the chaperone is released
- the MHC 1 travels in vesicles to the cell surface
What are the steps for MHC 2 antigen processing?
- internalization of target molecules
- digestion
- synthesis of MHC 2
- co-localization of MHC and antigen compartments
- peptide loading
- transport to cell surface
Describe 1. antigen internalization for MHC 2 (4)
- extracellular proteins are internalized via phagocytosis or endocytosis
- macrophages: phagocytosis
- B-cells: endocytosis
- peptides are held in phagosomes or endosomes
Describe 2. peptide generation for MHC 2 (5)
- antigen is degraded with the endocytic pathway
- early endosome
- late endosomes
- lysosomes
- peptides are degraded to 13-18 amino acids
Describe 3.Synthesis of MHC 2 (1)
-in the endoplasmic reticulum they’re stabilized with chaperone proteins
Describe 4.Co-localization for MHC 2 (1)
Vesicles containing newly-synthesized MHC 2 travel from the ER, through the golgi and eventually fuse with endolysomes
Describe 5.Peptide loading MHC 2 (1)
-chaperone protein is degraded and replaced by peptide fragments
Describe 6. Surface expression MHC 2 (2)
- once loaded the MHC 2 travels to the cell surface
- fusion of vesicle with the cytoplasmic membrane leads to expression of loaded MHC 2 on the cell surface
