Unit 2- MHC

Question 1

What is MHC?

Why is it essential?

Answer 1

major histocompatibility complex
set of genes on chromosome 6 that code for cell surface proteins- essential for the immune system to recognise foreign molecules

Question 2

What are the two classes of MHC and why are they different?

Answer 2

MHC Class I present peptide antigens derived from pathogens that replicate inside the cell
MHC Class II present peptides from pathogens that are present outside the cell taken up by endocytic vesicles.

Question 3

Where are the two types of MHC molecules expressed?

Answer 3

MHC class I are expressed on nucleated cells
MHC Class II are expressed on antigen presenting cells e.g. dendritic cells, macrophages

Question 4

What kind of chains is MHC Class I made up of?

What is the chain linked to?

Answer 4

heavy chain, non-covalently linked to B2m (B2microglobulin)

Question 5

In MHC Class I how is the peptide binding site formed?

How is this structure supported?

Answer 5

Has three domains- alpha 1,2 and 3
Peptide binding site is formed by the folding of alpha 1 & 2.
Supported by alpha 3 and B2m.

Question 6

What chains does MHC Class II contain?

Answer 6

two non-identical transmembrane chains (alpha and beta)

Question 7

How many domains does MHC Class II have? How are these arranged?

Answer 7

4 domains

each chain contributes one domain to the peptide binding site and one Ig-like supporting domain

Question 8

Which chains form the peptide binding site of MHC Class II domains?

Answer 8

the two domains furthest from the membrane form the peptide binding site

Question 9

MHC is polygenic…

What does this mean?

Answer 9

contains several different MHC class I and MHC class II genes so every individual has a set of MHC molecules with different ranges of peptide binding specificities

Question 10

What does Polymorphism mean? Where does this reside in MHC?

Answer 10

multiple variants of each gene within the population- majority of polymorphism resides in the peptide binding groove.

Question 11

Where is the variability in MHC class I?

Answer 11

at different positions along the alpha 1 & 2 chains

Question 12

Where is the variability in MHC Class II?

Answer 12

found in the beta I region that line the wall and floor of the groove that binds the peptide

Question 13

You inherit one MHC molecule from your mother and one from your father.. this means they are __-_______ __________

Answer 13

co-dominantly expressed

Question 14

Why do we need MHC polymorphism?

Answer 14

• can prevent pathogen spreading as a group will have different susceptibilities to a pathogen
• in large populations polymorphism at each locus can double the MHC molecules expressed
• increases likelihood of responding to a pathogen

Question 15

What are CD8 T cells?
When recognising an antigen, which MHC class is in association with it?

Answer 15

CD8= cytotoxic T cells

MHC Class I

Question 16

What are CD4 T cells?
When recognising an antigen which MHC class is association with it?

Answer 16

T helper cells

MHC Class II

Question 17

Briefly explain the MHC Class I antigen pathway?

Answer 17

1. New Viral proteins made in cellular ribosomes in the cytoplasm
2. Proteins are degraded to peptides in the cytoplasm
3. Peptides are then transported into the ER
4. MHC Class I molecules bind to peptides in the ER and are transported to the infected cells surface

Question 18

Briefly explain the MHC Class II antigen pathway?

Answer 18

1. Macrophages phagocytose extracellular bacteria and degrade their proteins in endocytic vesicles
2. MHC Class II molecules from the ER bind peptides in the endocytic vesicles and then transport them to the cell surface