MHC and Antigen Presentation Flashcards
What type of antigens do T lymphocytes “see”?
Peptides presented in association with major histocompatibility
Where do T cells come from?
Start in your bone marrow and mature in your thymus
What is MHC class I pathway for?
Intracellular antigen processing for viruses and tumors
What does MHC class I pathway present?
Endogenous antigens such as viral proteins or tumor proteins
What are epitopes?
The few amino acids that can be recognised by the T-cell receptors
What are MHC molecules called in humans?
Human Leukocyte Antigen
What is unique about MHC?
It is highly polymorphic
What are the two types of MHC molecules?
Class I and Class II
How are MHC genes expressed?
Co-dominantly
i.e. inherit one gene from mum and one from dad
What is MHC class I expressed on?
All nucleated cells
What is MHC class II expressed on?
Only on antigen presenting cells
What type of T cells recognise MHC class I?
CD8+ T cells
What type of T cells recognise MHC class II?
CD4+ T cells
What do CD8+ T cells do?
Kill infected cells
What do CD4+ T cells do?
Coordinate the immune response
How does MHC class I work?
- Virus infects cell makes viral protein
- Proteins marked for destruction sent to proteasome which chops them into smaller peptides
- Peptides transported to ER by TAP
- Peptides are loaded onto the MHC
- MHC travels to cell surface and is presented to CD8+ T cells
How does MHC class II work?
- Immune cell engulfs bacteria creating a phagosome
- Phagosome fuses with a lysosome which breaks down the bacteria into small peptides
- MHC class II molecules produced in ER but prevented from binding due to CLIP
- When phagolysosome and MHC merge HLA-DM removes clip allowing peptides to bind to MHC
- MHC cell travels to cell surface and presents CD4+ T cells
What is cross presentation?
When a dendritic cell takes in extracellular antigens and loads them onto MHC class I instead
