Antigen Presentation (Lec 7)

Question 1

T Cell Receptor (TCR) Structure

Answer 1

• Made up of 2 polypeptides, alpha chain and beta chain
• Also have a variable region (V𝛼 and Vβ) and constant region (C𝛼 and Cβ)

Question 2

Antigen Processing

Answer 2

• Proteins are degraded into peptides that can be loaded
  onto MHC molecules
• first step in antigen presentation—telling T cells what to attack

Question 3

Antigen Processing for MHC Class I Peptides

Answer 3

• Intracellular peptides are generated by degradation of proteins in cytosol
• MHC class 1 gets assembled in ER
• it associated with a bunch of proteins including TAP
• TAP brings in peptides that were degraded in the cytosol to the ER
• one of the peptides gets placed on MHC class 1
• it then gets sent to plasma membrane to be expressed

Question 4

Endoplasmic Reticulum
Aminopeptidase (ERAP)

Answer 4

• Peptides must be within
  a specific size range for
  MHC Class I
• trims peptides to the
  right size for MHC Class I
  antigen presentation
• happens before it leaves the ER but after peptide associates with MHC class 1

Question 5

Antigen Processing for MHC Class II Peptides

Answer 5

• PAPC will uptake pathogen from extracellular space
• gets broken down as it moves through endolysosomal pathway
• MHC class 2 gets made in the ER, then moves into a vesicle
• invariant chain bound to MHC class 2 gets cleaved, CLIP (a piece) gets left bound
  -CLIP remains bound until fusion
• vesicles with pathogen and MHC class 2 fuse and peptides get loaded onto MHC class 2

Question 6

Invariant chain

Answer 6

• involved in MHC class antigen presentation
• takes up binding pocket on MHC class 2
• does not allow peptide interaction
• prevents binding of self and MHC class 1 peptides in the ER

Question 7

Cross-Presentation

Answer 7

• only for pAPCs
• Antigens are brought in through MHC Class II pathway in pAPCs but presented on MHC Class I to activated CD8 T cells