L8 - Antigen Presentation

Question 1

What is the structure of MHC I?

Answer 1

3 extracellular domains, α1 + α2 (peptide binding region), α3 (Ig-like region) and a β2 microglobulin

Question 2

Are the peptides fixed within the MHC I molecule?

Answer 2

Yes

Question 3

Describe MHC I Antigen Presentation

Answer 3

1. Pathogen infection, synthesis of viral antigens
2. Proteasome degrades antigen (cytoplasm)
3. Peptides enter ER via TAP
4. Peptides inserted onto MHC I
5. MHC I / Peptide complex transported along secretory pathway to plasma membrane

Question 4

What is the structure of MHC II?

Answer 4

2 chains, α chain (α1 and α2) and β chain (β1 and β2). The 1s are peptide binding regions, the 2s are Ig-like regions

Question 5

Are the peptides fixed within the MHC II molecule?

Answer 5

No

Question 6

Describe MHC II Antigen Presentation

Answer 6

1. Antigen presenting cell endocytoses antigen
2. Endosomal proteases degrade antigen
3. Antigenic peptides contained in endosomal compartments
4. MHC II molecules synthesized in the ER (must travel to endosomal compartments)
5. Binds with Ii, transported to endosomes
6. Binding to antigenic peptides via Ii degradation
7. Transported to plasma membrane

Question 7

How do the conditions change between early endosomes, late endosomes and lysosomes?

Answer 7

1. pH decreases
2. Reducing condition increases
3. Proteases increases

Question 8

What does MHC II associate with to prevent binding of ER components?

Answer 8

Invariant chain (Ii)
- CLiP region of Ii occupies peptide binding site

Question 9

How does MHC II associate with Ii?

Answer 9

Three MHC II αβ dimers associate in the ER with three Ii to form a [αβIi]3 nonamer

Question 10

Do MHC II molecules bind pre-formed antigenic peptides or do they bind longer peptides that are later trimmed?

Answer 10

Most likely both exist