MHC Class I Flashcards
What is the function of MHC Class I molecules?
To present endogenous antigens from within cells to CD8 plus cytotoxic T lymphocytes CTLs
What types of antigens are presented by MHC Class I molecules?
Endogenous antigens such as viral proteins and defective ribosomal products DRiPs
What is the structure of MHC Class I molecules?
One alpha chain with three domains alpha 1 alpha 2 and alpha 3 and a beta-2 microglobulin
Where are MHC Class I molecules expressed?
On all nucleated cells
What is the role of cytotoxic T lymphocytes CTLs?
To recognize and destroy infected or abnormal cells by interacting with MHC Class I molecules that are presenting endogenous antigens
What happens to viral proteins in the cytosol during antigen processing?
They are degraded into peptides by the proteasome
What is the proteasome?
A multi-catalytic protease complex that breaks down proteins into peptides for antigen presentation
What is the role of TAP in the MHC Class I pathway?
TAP1 and TAP2 form a transporter that moves peptides from the cytosol into the endoplasmic reticulum ER
What is the role of beta-2 microglobulin in MHC Class I?
It stabilizes the structure of MHC Class I and assists in peptide binding
Where are peptides loaded onto MHC Class I molecules?
In the endoplasmic reticulum ER
What is the peptide-binding groove of MHC Class I molecules?
A cleft between the alpha 1 and alpha 2 helices where peptides of 8 to 9 amino acids are tightly bound
What is the immunoproteasome?
A modified version of the proteasome that generates peptides optimized for MHC Class I binding
What are anchor residues in peptides presented by MHC Class I?
Specific amino acids in peptides that interact with the MHC binding pocket
What is cross-presentation or cross-priming?
The process by which exogenous antigens are presented on MHC Class I molecules by professional antigen-presenting cells such as dendritic cells
What happens to peptides after they are transported into the ER by TAP?
They are trimmed by ER aminopeptidases to fit the MHC Class I binding groove
What is the role of the peptide-loading complex?
To assist in the assembly of MHC Class I molecules with peptides in the ER
How does MHC Class I antigen presentation enable immune surveillance?
It allows the immune system to detect and respond to infections or abnormalities inside cells
What happens to MHC Class I peptide complexes after assembly in the ER?
They are transported through the Golgi apparatus to the cell surface for presentation to CD8 plus T cells
What are defective ribosomal products DRiPs?
Abnormal or misfolded proteins generated during translation that are rapidly degraded and presented by MHC Class I molecules
What is the dual role of MHC Class I molecules in viral infections?
To present viral peptides to CTLs and to allow the immune system to detect virally infected cells
How are peptides selected for binding to MHC Class I molecules?
Peptides with specific anchor residues and lengths are selected to fit the MHC Class I binding groove
What is the impact of viral evasion on MHC Class I antigen presentation?
Some viruses produce proteins that interfere with MHC Class I expression or peptide loading to evade immune detection
What is the importance of cross-presentation in immunity?
It allows professional antigen-presenting cells to initiate CD8 plus T cell responses against pathogens not directly infecting them
How does the MHC Class I pathway contribute to adaptive immunity?
By presenting intracellular antigens it activates CD8 plus T cells which are crucial for the adaptive immune response
What is the order of the MHC Class I Pathway?
1- Synthesis of MHC Class I Molecules
2- Antigen Processing in the Cytosol
3- Peptide Transport to the ER
4- Peptide Loading
5- MHC Class I Complex Formation
6- Transport to the Cell Surface
7- Presentation to CD8+ T Cells
