MHC Class I

Question 1

What is the function of MHC Class I molecules?

Answer 1

To present endogenous antigens from within cells to CD8 plus cytotoxic T lymphocytes CTLs

Question 2

What types of antigens are presented by MHC Class I molecules?

Answer 2

Endogenous antigens such as viral proteins and defective ribosomal products DRiPs

Question 3

What is the structure of MHC Class I molecules?

Answer 3

One alpha chain with three domains alpha 1 alpha 2 and alpha 3 and a beta-2 microglobulin

Question 4

Where are MHC Class I molecules expressed?

Answer 4

On all nucleated cells

Question 5

What is the role of cytotoxic T lymphocytes CTLs?

Answer 5

To recognize and destroy infected or abnormal cells by interacting with MHC Class I molecules that are presenting endogenous antigens

Question 6

What happens to viral proteins in the cytosol during antigen processing?

Answer 6

They are degraded into peptides by the proteasome

Question 7

What is the proteasome?

Answer 7

A multi-catalytic protease complex that breaks down proteins into peptides for antigen presentation

Question 8

What is the role of TAP in the MHC Class I pathway?

Answer 8

TAP1 and TAP2 form a transporter that moves peptides from the cytosol into the endoplasmic reticulum ER

Question 9

What is the role of beta-2 microglobulin in MHC Class I?

Answer 9

It stabilizes the structure of MHC Class I and assists in peptide binding

Question 10

Where are peptides loaded onto MHC Class I molecules?

Answer 10

In the endoplasmic reticulum ER

Question 11

What is the peptide-binding groove of MHC Class I molecules?

Answer 11

A cleft between the alpha 1 and alpha 2 helices where peptides of 8 to 9 amino acids are tightly bound

Question 12

What is the immunoproteasome?

Answer 12

A modified version of the proteasome that generates peptides optimized for MHC Class I binding

Question 13

What are anchor residues in peptides presented by MHC Class I?

Answer 13

Specific amino acids in peptides that interact with the MHC binding pocket

Question 14

What is cross-presentation or cross-priming?

Answer 14

The process by which exogenous antigens are presented on MHC Class I molecules by professional antigen-presenting cells such as dendritic cells

Question 15

What happens to peptides after they are transported into the ER by TAP?

Answer 15

They are trimmed by ER aminopeptidases to fit the MHC Class I binding groove

Question 16

What is the role of the peptide-loading complex?

Answer 16

To assist in the assembly of MHC Class I molecules with peptides in the ER

Question 17

How does MHC Class I antigen presentation enable immune surveillance?

Answer 17

It allows the immune system to detect and respond to infections or abnormalities inside cells

Question 18

What happens to MHC Class I peptide complexes after assembly in the ER?

Answer 18

They are transported through the Golgi apparatus to the cell surface for presentation to CD8 plus T cells

Question 19

What are defective ribosomal products DRiPs?

Answer 19

Abnormal or misfolded proteins generated during translation that are rapidly degraded and presented by MHC Class I molecules

Question 20

What is the dual role of MHC Class I molecules in viral infections?

Answer 20

To present viral peptides to CTLs and to allow the immune system to detect virally infected cells

Question 21

How are peptides selected for binding to MHC Class I molecules?

Answer 21

Peptides with specific anchor residues and lengths are selected to fit the MHC Class I binding groove

Question 22

What is the impact of viral evasion on MHC Class I antigen presentation?

Answer 22

Some viruses produce proteins that interfere with MHC Class I expression or peptide loading to evade immune detection

Question 23

What is the importance of cross-presentation in immunity?

Answer 23

It allows professional antigen-presenting cells to initiate CD8 plus T cell responses against pathogens not directly infecting them

Question 24

How does the MHC Class I pathway contribute to adaptive immunity?

Answer 24

By presenting intracellular antigens it activates CD8 plus T cells which are crucial for the adaptive immune response

Question 25

What is the order of the MHC Class I Pathway?

Answer 25

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