Lecture 7 - Antigen Processing

Question 1

Where (cell cytosol or exogenous) does antigen that is presented via MHC I come from?

Answer 1

Cytosol OR exogenous via the cross-presentation pathway

Question 2

What kind (foreign vs. self) of antigen is usually presented on MHC I?

Answer 2

Self usually - fragments of old cytosolic proteins digested by proteosome.

Question 3

Name three categories of foreign/diseased antigen source that might be presented on MHC I.

Answer 3

Viral
Neoplastic
Parasitic

Question 4

Which cell types do NOT express MHC I?

Answer 4

Non-nucleated cells e.g RBC

CNS neurons

Question 5

Where (cell cytosol or exogenous) does antigen that is presented via MHC II come from?

Answer 5

Exogenous only

Question 6

Which MHC molecule and pathway do B cells use when they present antigen captured by membrane-bound antibodies?

Answer 6

MHC II - exogenous ag pathway

Question 7

Which presentation pathway is used by most vaccines?

Answer 7

MHC II

Question 8

Which protein binds the MHC I alpha chain until the beta-2 microglobulin is ready?

Answer 8

Calnexin

Question 9

Which two proteins block the MHC I antigen-binding-site until cytosolic antigen arrives?

Answer 9

ERP57/ calrticulin and tapasin

Question 10

Which protein imports peptides from the cytosol into the ER for MHC I loading? Does it bind any proteins to faciliate this?

Answer 10

TAP

Yes, binds tapasin

Question 11

Give one virus which blocks peptide entry to the ER and give its mechanism

Answer 11

Herpes simplex -
blocks peptide binding to TAP via ICP47 protein

HCMV - blocks TAP ATPase activity via US6 protein

Bovine herpes - inhibits TAP peptide transport

Question 12

Give one virus which causes retention of MHC I in the ER. How do they do this?

Answer 12

Adenovirus (via E19 protein) - competitive inhibition of tapasin

HCMV - Interfere with tapasin function

murine CMV

Question 13

Give ones virus that degrades MHC I

Answer 13

HCMV, murine gamma herpes virus

Question 14

Give one virus that binds MHC I at the cell surface

Answer 14

Murine CMV via US11 and derlin

Question 15

In which species do activated T cells express MHC II?

Answer 15

Humans and ruminants

Question 16

Where in the cell are MHC I molecules loaded? What about MHC II?

Answer 16

MHC I = endoplasmic reticulum

MHC II = lysosome

Question 17

What structure prevents MHC II binding self-peptide?

Answer 17

Invariant chain (initially), then CLIP later

Question 18

How many MHC II can the invariant chain bind at once?

Answer 18

Three

Question 19

What molecule needs to bind MHC II for CLIP to leave?

Answer 19

HLA-DM

Question 20

In which ‘direction’ does cross presentation occur?

Answer 20

Exogenous ag > MHC I

Don’t get endogenous ag > MHC II

Question 21

How does exogenous antigen get into the ER?

Answer 21

Exported out of phagosome by Sec61. From cytosol, moved into ER by TAP.

Question 22

Why is cross presentation important?

Answer 22

Activation of CD8 T cells specific for virus that doesnt infect dendritic cells or other APCs.