Antigen presentation

Question 1

what occurs to the antigens from the pathogen ?

Answer 1

they are taken up from the extracellular space into an intracellular vesicle. In the early endosomes the pH is neutral however the vesicle becomes acidic and this activates the proteases that breaks down the antigen into peptide fragments. The vesicle containing the peptides then with the vesicle containing the MHC class II molecules.

Question 2

what is the epitope on the antigen recognised by ?

Answer 2

T cell as the antigen is broken down to expose the epitope.

Question 3

why does the antigen need to be broken down to expose the epitope ?

Answer 3

as the epitope is often buried within the antigen molecule.

Question 4

what happens after the epitope is exposed?

Answer 4

binds to the self molecule , an MHC molecule. The T cell receptor then binds to a complex of MHC molecule and epitope peptide.

Question 5

what is the MHC ?

Answer 5

major histocompatibility complex is a set of genes that code for cell surface proteins essential for the acquired immune system to recognise foreign molecules in vertebrates, which in turn determines histocompatibility.

Question 6

the 2 classes of MHC have a similar 3D structure but what about the 2 subunit conformations?

Answer 6

they are distinct and different

Question 7

what are the CD4+ peptides presented too ?

Answer 7

the MHC class II molecules

Question 8

what are the CD8+ peptides presented too ?

Answer 8

the MHC class I molecules

Question 9

what antigens are the MHC class I normally for ?

Answer 9

intracellular

Question 10

MHC class II antigens ?

Answer 10

extracellular

Question 11

when a viral infection enters what does the nucleus release ?

Answer 11

viral proteins called endogenous antigen (intracellular)

Question 12

what does this cause?

Answer 12

activates the proteasome which is a complex that degrades proteins down to peptides that are 8 to 9 amino acids long. It is these peptides that associate and bind with the MHC class I receptors.

Question 13

what are TAP 1 and TAP 2 ?

Answer 13

are peptides transporters then travel in the Golgi before reaching the surface to present to Cd8+ T cells which leads to cell killing.

Question 14

give examples of extracellular antigens ?

Answer 14

malaria and bacteria

Question 15

what is the exogenous antigen processed by ( extracellular)

Answer 15

processed by the endosomes and they are broken down to fuse with the Class II MHC that are made in the ER. Once the MHC class II and exogenous peptides fuse they reach the cell surface and present to Cd4+ cells.

Question 16

what are the only professional antigen presenting cells in MHC class II ?

Answer 16

dendritic cells

Question 17

what type of antigens do dendritic cells process ?

Answer 17

a wide array of pathogens

Question 18

are the 2 classes of MHC molecules expressed the same amount on cells ?

Answer 18

no , they are expressed differentially

Question 19

why is it useful that there is a lot of diversity in the MHC haplotypes ?

Answer 19

this Increases the range of peptides presented to the immune system within species and reduces the chance of a pathogen evading the immune system.

Question 20

What does the MHC polymorphism affect ?

Answer 20

the antigen recognition by the T cell by influencing both peptide binding and the contact between the T cell receptor and the MHC molecule.

Question 21

for recognition in a T cell to occur , what is needed ?

Answer 21

you need the correct MHC , peptide antigen and TCR