Final MHC

Question 1

What are and what do MHC molecules do?

Answer 1

• they display antigens to T cells

- cell surface glycoproteins

Question 2

How many classes of MHC are there

Answer 2

3

Question 3

What is special about MHC genes?

Answer 3

Polygenic, multiple genes for the class (1, 2, 3)

Question 4

Which chromosome is the MHC gene complex for humans and mice?

Answer 4

• 6

- 17

Question 5

Explain class 1 MHC?

Answer 5

• present altered self antigens or viruses to activate cytotoxic T cells
• found on nearly all nucleated cells of the body
• each gene encodes an alpha chain protein

Question 6

Explain Class 2 MHC?

Answer 6

• present processed extracellular bacteria to helper T cells
• expressed only on membranes of antigen presenting cells (macrophage, dendritic cells, B cells)
• each region encodes both an alpha and beta chain

Question 7

Within a population is there a lot or a bit of MHC diversity?

Answer 7

-a lot of diversity between species

Question 8

For individuals, is there diversity in MHC?

Answer 8

No, all MHC molecules in individuals are the same

Question 9

Where does the diversity for MHC come from?

Answer 9

Polymorphism, multiple alleles within the MHC gene loci

Question 10

How many MHC 1 and 2 alleles do you inherit from mom and dad

Answer 10

• 3 MHC 1 from mom an 3 from dad

- 3 MHC 2 from mom and 3 from dad

Question 11

How many MHC 1’s are expressed?

Answer 11

All 6 on a nucleated cell

Question 12

How many MHC’s are expressed on APC’s?

Answer 12

12 MHC’s

Question 13

Describe MHC 1 peptide bonding?

Answer 13

• can only hold a peptide of 8-10 amino acids

- anchor residues hold peptide in place

Question 14

Describe MHC 2 peptide bonding

Answer 14

• can hold a peptide of 13-18 amino acids
• peptide is exposed and flat across the surface
• anchor points distributed across ends and centre of peptide
• interaction involves hydrophobic residues

Question 15

What is antigen processing?

Answer 15

The degradation of antigens into peptides

Question 16

What is antigen presentation?

Answer 16

Describes the binding of the peptide by MHC and displaying the peptide at the cell surface to interact with T cells

Question 17

Where are MHC 1 antigens processed?

Answer 17

In the cytoplasm

Question 18

Where are MHC 2 antigens processed?

Answer 18

In the endocytic pathway

Question 19

What is the purpose of antigen processing?

Answer 19

To generate peptides that will fit in the MHC binding cleft

Question 20

What are the steps of MHC 1 antigen processing?

Answer 20

1. identification and cleavage of target proteins
2. transport to endoplasmic reticulum
3. loading onto MHC 1
4. expression on cell surface

Question 21

1, 2. Describe identification and cleavage of target proteins and the transport for MHC 1?

Answer 21

• proteins are degraded by proteasomes
• peptides are then transported from the cytoplasm to the endoplasmic reticulum by the transporter of antigenic peptides (TAP)

Question 22

3, 4. Describe the loading and expression of MHC 1?

Answer 22

• peptides are loaded onto pre-formed MHC 1
• stabilized by chaperone proteins
• once a peptide is loaded the chaperone is released
• the MHC 1 travels in vesicles to the cell surface

Question 23

What are the steps for MHC 2 antigen processing?

Answer 23

1. internalization of target molecules
2. digestion
3. synthesis of MHC 2
4. co-localization of MHC and antigen compartments
5. peptide loading
6. transport to cell surface

Question 24

Describe 1. antigen internalization for MHC 2 (4)

Answer 24

• extracellular proteins are internalized via phagocytosis or endocytosis
• macrophages: phagocytosis
• B-cells: endocytosis
• peptides are held in phagosomes or endosomes

Question 25

Describe 2. peptide generation for MHC 2 (5)

Answer 25

- antigen is degraded with the endocytic pathway - early endosome - late endosomes - lysosomes - peptides are degraded to 13-18 amino acids

Question 26

Describe 3.Synthesis of MHC 2 (1)

Answer 26

-in the endoplasmic reticulum they're stabilized with chaperone proteins

Question 27

Describe 4.Co-localization for MHC 2 (1)

Answer 27

Vesicles containing newly-synthesized MHC 2 travel from the ER, through the golgi and eventually fuse with endolysomes

Question 28

Describe 5.Peptide loading MHC 2 (1)

Answer 28

-chaperone protein is degraded and replaced by peptide fragments

Question 29

Describe 6. Surface expression MHC 2 (2)

Answer 29

- once loaded the MHC 2 travels to the cell surface | - fusion of vesicle with the cytoplasmic membrane leads to expression of loaded MHC 2 on the cell surface