Processing and Presentation of Antigen

Question 1

Which cells have MHCI?

Answer 1

All nucleated cells in the body

Question 2

What do the cells use MHCI to do?

Answer 2

Alert CTL

Question 3

How do CTL kill?

Answer 3

Fas FasL

and perforin Granzyme path

Question 4

Human MHC and mouse MHC name:

Answer 4

HLA

H-2

Question 5

Role of MHC

Answer 5

Hold AAs to show TCR

Question 6

How do T cells recognise Ags?

Answer 6

Processed into peptides and presented by MHC

Question 7

Where is MHCII found?

Answer 7

On Professional APCs like macrophages, dendritic cells and B cells, on thymic epithelium and activated T cells

Question 8

Difference in job between MHC I and II

Answer 8

MHCI - specialised for alerting CTL about intracellular infections
MHCII - activates Th cells

Question 9

MHC I and II types:

Answer 9

MHC I: HLA - A, B, C

MHC II: HLA - DP, DQ, DR

Question 10

Variability in MHC explain (why do we get 6 MHCI)?

Answer 10

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

Question 11

Alpha and Beta chain in MHC I, + which MHC I type is more variable?

Answer 11

MHC I beta doesn’t vary, alpha does alot

HLA B is most variable, HLA A is least

Question 12

How do you get the numbers for the MHC?

Answer 12

Combination of alpha and beta chains

Question 13

Structure of an MHC:

Answer 13

Beta pleated sheets and on top - 2 alpha helices

Groove where peptide sits

Question 14

Dif in structure of MHC I and II: 3

Answer 14

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

Question 15

Varying bit in the MHC:

Answer 15

alpha helices, and cleft - in MHC I the beta bit doesnt touch the cleft

Question 16

Specificity of MHC:2

Answer 16

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)

Question 17

MHC interaction with T cell:

Answer 17

MHCI and CD8+ –> CD8 sees non polym bit, TCR sees AAs and bit of alpha helices on MHC
MHC II and CD4+ same

Question 18

Length of AA shown by each MHC:

Answer 18

MHC I : 8-9 AA long

MHC II: about 15 aa long or longer

Question 19

Exogenous vs endogenous peptides:

Answer 19

Endogenous by MHC I - cell is infected

Exogenous by MHC II - phagocytosed or endocytosed

Question 20

MHC I processing of peptide explain:

Answer 20

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

Question 21

MHC II processing of peptide pathway:

Answer 21

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

Question 22

What is cross presentation?

Answer 22

When MHCII shows endog or MHC I shows exog