antigen processing and presentation

What is the purpose of antigen presentation?

Allows T cells to recognize antigen and initiate immune responses

Where do most MHC I antigens originate?

Intracellular proteins

What marks proteins for degradation?

Ubiquitin

What does the proteasome do?

Breaks intracellular proteins into peptides

What does TAP do?

Transports peptides from cytosol into ER

Where are peptides loaded onto MHC I?

Endoplasmic reticulum

What does ERAP1 do?

Trims peptides in the ER

What does tapasin do?

Helps load peptides onto MHC I

Which T cells recognize MHC I?

CD8 T cells

What is the MHC I pathway in order?

Intracellular protein → proteasome → TAP → ER → MHC I → surface → CD8

What is cross-presentation?

Extracellular antigen presented on MHC I

Which cells are especially good at cross-presentation?

cDC1 dendritic cells

Why is cross-presentation important?

Primes naive CD8 T cells against extracellularly acquired antigens

Does cross-presentation use MHC I or II?

MHC I

Where do most MHC II antigens originate?

Internalized extracellular proteins

How do APCs take up extracellular antigens?

Endocytosis or phagocytosis

Where are MHC II peptides generated?

Acidified endosomes and lysosomes

What is the function of invariant chain (Ii)?

Blocks premature binding and directs MHC II to endosomes

What is CLIP?

Invariant-chain fragment occupying MHC II groove

What does HLA-DM do?

Removes CLIP and promotes antigen peptide loading

What does HLA-DO do?

Regulates HLA-DM activity

Which T cells recognize MHC II?

CD4 T cells

What is the MHC II pathway in order?

Extracellular antigen → endocytosis → endosome → Ii/CLIP → HLA-DM → MHC II → surface → CD4

What is MARCH-1?

E3 ubiquitin ligase that regulates MHC II turnover

What happens to MARCH-1 after dendritic-cell activation?

Its expression decreases

What happens to surface MHC II after dendritic-cell activation?

Peptide-MHC II complexes become more stable

Which APC is best at activating naive T cells?

Dendritic cells

What is the main antigen-presentation role of macrophages?

Present antigen to effector CD4 T cells

What is the main antigen-presentation role of B cells?

Present BCR-captured antigen to helper T cells

Which pathway uses the proteasome and TAP?

MHC I pathway

Which pathway uses invariant chain and CLIP?

MHC II pathway

Which molecule removes CLIP from MHC II?

HLA-DM

Which pathway normally presents intracellular antigens?

MHC I → CD8

Which pathway normally presents internalized extracellular antigens?

MHC II → CD4

What is the major exception to extracellular antigen → MHC II?

Cross-presentation on MHC I