2.1 Antigen Presentation

Question 1

What is the first law of immunology?

Answer 1

Lymphocytes detect antigen in a different ways
- B cell receptors detect whole antigen on pathogen surface
- T cell receptors detect displayed digested antigen fragments

Question 2

What is the second law of immunology?

Answer 2

MHC I present peptides from pathogens in intracellular fluid (cytoplasm)

MHC II present peptides from pathogens in extracellular fluid (tissue fluid)

Question 3

Where do viruses v bacteria replication?

Answer 3

Viruses om cytoplasm
Bacteria in tissue fluid

Question 4

Describe the structure of MHC Class I molecule

Answer 4

3 alpha domains anchored by a transmembrane anchor domain. Stabilised by a protein, B2 globulin, that ensures correct protein folding

Question 5

Describe the structure of MHC class II molecules

Answer 5

alpha and beta polypeptide chains each anchored by a transmembrane anchor domain.

Question 6

Describe the peptide binding groove

Answer 6

Peptide anchored by three critical anchor residues (aas at a specific position) Different peptides with correct residue positions can binds so MHC can present variety of peptides.

Question 7

Describe the MHC I pathway

Answer 7

• Proteasome breaks viral structural proteins into peptides
• Transported to ER by TAP transporters
• Peptide epitope binds MHC I if correct anchor residues present
• MHC I transporter to cell surface for recognition by CD8 T cells

Question 8

Describe the synthesis of MHC class II molecules

Answer 8

• Newly synthesised MHC II molecules stabilised by INVARIANT CHAIN chaperone protein that blocks endogenous peptides from binding in ER
• MHC II enter secretory pathway to golgi to be packaged into vesicle
• Invarient chain degrades to leave CLIP peptide still blocking binding site

Question 9

Describe antigen processing by the MHC class II molecule

Answer 9

• Endocytosed antigens are digested into peptides by lysosomal acid and proteases
• CLIP peptide is displaced by foreign peptide
• MHC II peptide complex transported to cell surface to be recognised by CD4 T cell

Question 10

Which CD molecule interacts with which MHC class?

Answer 10

CD8 = MHC I (intracellular infection)
CD4 = MHC II (extracellular infection)

Question 11

What are antigen-presenting cells (APCs)

Answer 11

Express both MHC I and MHC II

Dendritic cells present to naive T cells in lymphoid tissues - professional APCs that stimulate proliferation and differentiation.

Macrophages and B cells present to mature CD4 Th cells

Question 12

Describe dendritic cells

Answer 12

• Differentiate from circulating monocytes
• Immature DCs at epithelial surfaces to engulf antigens
• Migrate via afferent lymphatics to LN to process antigen
• Reside in LN paracortex to present antigen to naive T cells