1. What are the two major compartments of the cell?
A. Cytosol and mitochondria
B. Cytosol and nucleus
C. Cytosol and vesicular system
D. ER and Golgi

B. Cytosol and nucleus

2. Why are the cytosol and vesicular system kept separate?
A. To regulate calcium
B. To prevent viral and bacterial overlap
C. Because viruses exploit cytosol, bacteria exploit vesicular compartments
D. To maintain osmotic balance

C. Because viruses exploit cytosol, bacteria exploit vesicular compartments

3. Which type of antigen is presented by MHC class I molecules?
A. Exogenous
B. Endogenous
C. Lipid
D. Polysaccharide

B. Endogenous

4. What is the role of TAP1/2 in antigen presentation?
A. Binds peptide to MHC
B. Transports peptides into the ER using ATP
C. Degrades misfolded proteins
D. Removes CLIP from MHC class II

B. Transports peptides into the ER using ATP

5. What is the function of calnexin?
A. Transports peptides into the cytosol
B. Ensures proper folding of MHC class I before β2-microglobulin binds
C. Removes CLIP from MHC class II
D. Cuts peptides to 8 amino acids

B. Ensures proper folding of MHC class I before β2-microglobulin binds

6. Which enzyme trims peptides in the ER to the correct size for MHC class I binding?

A. Tapasin

B. ERAP

C. Calreticulin

D. ERp57

B. ERAP

7. The proteasome breaks down:

A. Damaged DNA

B. Misfolded or old proteins into small peptides

C. Cytokines

D. Lipids

B. Misfolded or old proteins into small peptides

8. The immunoproteasome is formed in response to:

A. Heat shock

B. Cytokines such as IFN-γ

C. Nutrient deficiency

D. Lipid accumulation

B. Cytokines such as IFN-γ

9. What is the purpose of the invariant chain (Ii)?

A. Loads peptide onto MHC II

B. Blocks premature peptide binding and directs MHC II to endosome

C. Removes CLIP from MHC II

D. Prevents folding of MHC I

B. Blocks premature peptide binding and directs MHC II to endosome

10. The CLIP fragment is:

A. A part of the invariant chain that remains in the peptide-binding groove

B. A transport protein

C. A cytokine

D. A TAP cofactor

A. A part of the invariant chain that remains in the peptide-binding groove

11. What does HLA-DM do?

A. Blocks CLIP binding

B. Degrades peptides

C. Removes CLIP and helps peptide loading on MHC II

D. Recycles MHC II to the ER

C. Removes CLIP and helps peptide loading on MHC II

12. What family of molecules presents lipid antigens?

A. CD3

B. CD4

C. CD1

D. TAP

C. CD1

13. CD1 molecules are structurally similar to:

A. MHC class I

B. MHC class II

C. Both A and B

D. Neither

A. MHC class I

14. Which antigen-presenting cell initiates adaptive immunity?

A. Macrophage

B. B cell

C. Dendritic cell

D. Neutrophil

C. Dendritic cell

15. Which MHC class is associated with exogenous antigen presentation?

A. MHC class I

B. MHC class II

C. CD1

D. HLA-C

B. MHC class II

ERAP

Removes amino acids from peptide N-terminus

Tapasin

Ensures high-affinity peptide binds to MHC I

Calreticulin

Chaperone protein assisting MHC folding

TAP1/2

Transports peptides into the ER using ATP

CLIP

Blocks premature peptide binding to MHC II

16. Define self-antigen vs. non-self antigen and explain why presentation of self-antigen is normal.

Self = own proteins; Non-self = foreign. Self presentation = normal immune tolerance.

17. What is ERAD, and why is it necessary for protein quality control?

ERAD = ER-associated degradation of misfolded proteins

18. What is the peptide loading complex (PLC) and what are its components?

PLC = Tapasin, TAP1/2, ERp57, Calreticulin. Loads peptide onto MHC I

19. Define peptide editing and explain the role of tapasin.

Peptide editing = Tapasin ensures tight peptide binding to MHC I.

20. What is immunodominance? Name the three strength levels of epitopes.

Immunodominance = strongest epitope response (immunodominant > subdominant > cryptic).

21. Explain the role of cross-presentation and why it’s important.

Cross-presentation = exogenous antigen presented via MHC I → activates CD8+ T cells.

22. What are the three main antigen-presenting cells (APCs)?

Dendritic cells, macrophages, B cells.

23. Describe the process by which dendritic cells activate T cells.

DCs phagocytose antigen → migrate to lymph node → present via MHC II → activate naive T cells.

24. What are the two problems the invariant chain (Ii) solves for MHC class II?

Ii blocks endogenous peptide binding and directs MHC II to endosome.

25. Explain how MHC class I and MHC class II differ in antigen origin and the T cell type they activate.

MHC I = endogenous/CD8+; MHC II = exogenous/CD4+.