Lecture 11: Antigen Presentation

Question 1

What is antigen processing?

Answer 1

The conversion of native proteins into MHC-associated peptides

Question 2

MHC Class 1 presents peptide antigen derived from the _______ and Class 2 presents peptide antigen from ___________.

Answer 2

Cytosol

Intracellular Vesicles

Question 3

Macrophages (MO) take up particulates and present them to _____ which act back on the MO to stimulate ___________.

Answer 3

CD4

Microbicidal activity

Question 4

B cells endocytose _______ captured by the _____________ and activate helper T cells that promote antibody production

Answer 4

Ag

Ig receptor

Question 5

Outline the Class 1 pathway:

Answer 5

1. Proteasome digests proteins from intracellular pathogens into peptides
2. TAP1 and 2 gene products pump 8-16aa chains into the ER
3. Aminopeptidases (ERAAP) trim peptides to fit MHC class 1
4. Newly made MHC1α chains assemble with membrane-bound Calnexin in the ER
5. Binding of β2M dissociated Calnexin and then TAP is bound
6. Chaperone molecules, Calreticulin and Erp57 bind
7. Ag binds, folding completes
8. Transported via the Golgi to the cell surface

Question 6

MHC Class 2 α and β chains are found complexed to the __________ in the ER. _____ covers the binding site on the MHC. They then transported to an _______________.

Answer 6

Invariant chain (li)
CLIP
Endosomal/Lysosomal vesicle

Question 7

The low pH of the phagolysosome activates ________ which cleave ______ into peptides

Answer 7

Proteases

Proteins

Question 8

Outline the Class 2 Pathway:

Answer 8

1. Class 2 α and β chains complex with the invariant chain (li)
2. MHC is directed to the low pH phagolysosome by the li
3. The li is cleaved but CLIP remains on the binding site
4. HLA-DM binds and CLIP is released
5. Peptides derived from endocytosed pathogens can now bind

Question 9

What is cross-presentation?

Answer 9

Presenting Ag that wasn’t originally in the APC, ag wasn’t formed in their cytosol or endosomes (APC wasn’t infected)

Question 10

Briefly, describe the process of cross-presentation:

Answer 10

1. Endogenous protein Ag are endocytotically acquired
2. Ag is transferred from the phagolysosome to the cytosol
3. Ag is processed via the proteasome
4. Ag enters the Class 1 pathway