Processing and Presentation of Antigen Flashcards
Which cells have MHCI?
All nucleated cells in the body
What do the cells use MHCI to do?
Alert CTL
How do CTL kill?
Fas FasL
and perforin Granzyme path
Human MHC and mouse MHC name:
HLA
H-2
Role of MHC
Hold AAs to show TCR
How do T cells recognise Ags?
Processed into peptides and presented by MHC
Where is MHCII found?
On Professional APCs like macrophages, dendritic cells and B cells, on thymic epithelium and activated T cells
Difference in job between MHC I and II
MHCI - specialised for alerting CTL about intracellular infections
MHCII - activates Th cells
MHC I and II types:
MHC I: HLA - A, B, C
MHC II: HLA - DP, DQ, DR
Variability in MHC explain (why do we get 6 MHCI)?
2 copies of MHC, maternal and paternal. B is in same locus - but different sequence, so you get 3 MHC from mom, 3 from dad
If mom and dad same - 5 - homozygous
Alpha and Beta chain in MHC I, + which MHC I type is more variable?
MHC I beta doesn’t vary, alpha does alot
HLA B is most variable, HLA A is least
How do you get the numbers for the MHC?
Combination of alpha and beta chains
Structure of an MHC:
Beta pleated sheets and on top - 2 alpha helices
Groove where peptide sits
Dif in structure of MHC I and II: 3
MHC I: 3a, 1B, MHC II: 2a, 2B + two transmembrane segments
dif weights
MHC I peptide binding groove is closed at 2 ends
MHC II binding groove is open at ends so peptide can hang over the edge
Varying bit in the MHC:
alpha helices, and cleft - in MHC I the beta bit doesnt touch the cleft
Specificity of MHC:2
Size specific especially with MHC I
Also each MHC can bind a number of different peptides, what is needed is that at certain positions in AA sequence we need certain characteristics (eg to anchor in the groove)
MHC interaction with T cell:
MHCI and CD8+ –> CD8 sees non polym bit, TCR sees AAs and bit of alpha helices on MHC
MHC II and CD4+ same
Length of AA shown by each MHC:
MHC I : 8-9 AA long
MHC II: about 15 aa long or longer
Exogenous vs endogenous peptides:
Endogenous by MHC I - cell is infected
Exogenous by MHC II - phagocytosed or endocytosed
MHC I processing of peptide explain:
Usually worn out proteins in the cell are processed by proteosomes which was random
If infected - add enzymes to it and make it a immunoproteosome that cuts peptides in 8-9 aa lengths
MHCI is in the RER, Tap I and II pick up the peptides cut and inside the ER, they are associated with MHC I.
Once bound, take to cell surface and present
MHC II processing of peptide pathway:
Ag is phagocytosed or endocytosed and peptides cut to right length by enzymes
MHCII made in RER, put invariant chain inside so no other peptide binds
Take MHCII into vesicle, meet with peptides
Most Ii is degraded, CLIP is left
DO and DM take CLIP out and replace it with peptides
What is cross presentation?
When MHCII shows endog or MHC I shows exog
