4. Antigen Presentation And Processing

Question 1

Where can we find MHC1?

Answer 1

All nucleated cells

Question 2

Where can we find MHC2?

Answer 2

Only found on the surface of some cell types

Question 3

Structure of MHC1

Answer 3

Alpha 1-3, beta2m + TMD

Question 4

Structure of MHC2

Answer 4

Alpha1-2, beta1-2 + 2TMDs

Question 5

What does co-recognition mean?

Answer 5

That a TCR is able to recognize both the MHC molecule and the peptide piece presented by the MHC

Question 6

What does MHC restriction mean?

Answer 6

?

Question 7

Why is MHC1 only expressed on nucleated cells?

Answer 7

Because non-nucleated cells lack glycoproteins on the membrane and therefore can’t express this surface protein

Question 8

What is the function of MHC1?

Answer 8

Presentation of endogenous antigens to cytotoxic T cells

Question 9

Function of MHC2

Answer 9

Presents exogenous antigens to helper T cells

Question 10

On what chromosome can we find the genes encoding MHC molecules?

Answer 10

Chromosome 6, on the short arm

Question 11

Genetic features of MHC molecules

Answer 11

Polygenic: different genes can encode for proteins with overlapping functions (?)
Polymorphic: Different gene variants can encode for different proteins with different functions (?)
Co-dominantly inherited: if allele A is from egg and allele B is from sperm and they both are expressed (both appears on the surface of cells)

Question 12

What kind of peptides does MHC1 present?

Answer 12

Short, endogenous peptides: 8-9AA (peptide binding side similar to a fixed pocket)

Question 13

What kind of peptides does the MHC2 present?

Answer 13

Longer, exogenous peptides: 11-25AA

Peptide binding side similar to an open cleft

Question 14

Process of producing peptide fragment MHC1 + endogenous peptide

Answer 14

Viral DNA/RNA is integrated into nucleus of host cell -> produce viral RNA -> viral proteins -> viral proteins into proteasome (cuts proteins into peptides) in cytosol -> peptides loaded into lumen of RER (MHC1 molecules synthesized here at the same time) -> MHC1 binds peptide -> goes through golgi and finally arrives at the cell surface -> presentation to cytotoxic T cells

Question 15

Function of TAP (transporter associated with antigen processing)

Answer 15

ATP dependent transporters in the RER membrane that functions to take up the peptides that are more than 8 AA long and have carboxyl ends

Question 16

Process of producing peptide fragment MHC2 + exogenous peptide

Answer 16

Extracellular self or foreign protein is taken up by endocytosis ->endosomes fuse with lysosomes from golgi -> MHC2 molecules produced in the RER -> vesicles with MHC2 and peptide fragments fuse and are transported by exocytosis to the surface of the cell

Question 17

Antigen presentation by dendritic cells: where, to who

Answer 17

Carries the pathogen to the lymph node, presents antigen to naive T-cell

Question 18

Antigen presentation by B-cells and macrophages

Answer 18

Presents antigen to effector T-cell

Question 19

Proteins encoded by MHC class I genes

Answer 19

HLA-A, -B, -C

Question 20

Proteins encoded by MHC class II genes

Answer 20

HLA-DP, -DR, -DQ

Question 21

What chains bind peptide in MHC I?

Answer 21

Alpha chains

Question 22

Function of invariant chain(Ii)

Answer 22

• Binding to MHC II in RER to prevent self peptide from binding
• Targets MHC II for lysosome

Question 23

What is CLIP?

Answer 23

The remaining fragment of Ii cleaved when surroundings are acidic.

Question 24

Function of HLA-DM?

Answer 24

Helps separating CLIP from MHC II in the lysosome

Question 25

Which chains binds the peptide in MHC II?

Answer 25

Alpha and beta chains

Question 26

CD1 function

Answer 26

Has a structure similar to MHC I -> can present lipid Ag fragments