Antigen presentation Flashcards
(21 cards)
Describe the structure of immunoglobulins [6]
- dimer linked by disulphide bonds
- Y shaped
- light chain on upper outer part of Y
- heavy chain lower and inside part of the Y
- constant region at the bottom Y
- variable region at top of Y
What is FaB [4]
- fragment antifen binding
- light chain
- determines what antibody recognises
- joining multiple together allows for diversity
What is FC [3]
- fragment constant
- adaptor molecule
- other immune cell to identify variety of cel bodies
What is meant by a linear epitope
binding site on antigen recognised by antibodies by its linear sequence of amino acids
What is meant by conformational epitopes
binding site on antigen recognised by B/T cell receptors. Recognises non consecutive parts of the gene
Why is it important that antigens have both conformational and linear epitopes
can recognise both antibodies and misfiled proteins
Identify two differences between membrane bound and soluble immunoglobulins
- soluble does not have a binding domain
- soluble only secreted when B cell has been activated
Compare MHC I and MHC II [3]
- on all nucleated cells/ on phagocytic antigen present cells
- has beta 2 microglobulin/ does not have …
- peptide is well contained/ peptide is longer and sticks out
Define the term polymorphism
two alleles at single gene locus (one from each parent)
Define the term polygeny
presence of several different related genes with similar function
Explain what is meant by MHC restriction [2]
- for T cell to bind the peptide and MHC met be correct
- to ensure only infected, self cells are targeted
What types of pathogens do MHC II bind to the peptides of? [2]
- intravesicular
- extracellular / toxins
What are the four steps to antigen processing? [4]
antigen uptake
antigen processing
MHC biosynthesis
Peptide-MHC association
Describe the cytosolic pathway for antigen processing [7]
- antigen taken up from extracellular space
- acidification of vesicle (H+ in)
- activates proteases to degrade antigen into peptides
- peptides enter ER via TAP
- binds to MHC if HLA complex is complimentary
- vesicle formed
- travels to surface membrane via Golgi
Describe the extracellular pathway of antigen processing
8
- taken up by phagocytosis
- degrades and cut up in end-some/lysosome
- goes to ER
- invariant chain removed from MHCII
- fusese with vesicle containing peptides
- peptides fuse with MHCII
- creates stable complex
- go to cell membrane via Golgi
What are the difference between the cytosolic and extracellular pathways of antigen processing [4]
- peptide in cytosol/taken up through phagocytosis
- digestion of protein by proteasome/endosome or lysosome
- MHC I / MHC II
- activates CD8 cells/activates CD4 T cells
What are the similarities between the cytosolic and extracellular pathways for antigen processing [3]
- proteins digested into peptides
- both bind to MHC in the ER
- both transposed to membrane via Golgi
What is the role in B2m in antigen processing?
binds to chaperone proteins
What is the role of ERAAP
further trims peptides
What is epitope editing [2]
- not all peptides generated by ERAAP are good fit for MHCI
- multiple peptides are made until one fits the MCH I
Describe the loading of peptides to MHC II [7]
- acidification of vesicle
- causes invariant chain to be cleaved from MHC II
- leaves peptide fragment (CLIP) bound to MHC II
- vesicle containing peptide fragments bind to vesonble
- HLA - DM binds to MHC releasing CLIP
- allowing other peptides to bind
- MHC II to membrane
