Immunology 2

Question 1

which specific part of a pathogen do adaptive immune cell receptors (BCR or TCRs) target?

Answer 1

the epitopes on the antigen surface

Question 2

what do BCRs recognise?

Answer 2

unprocessed antigens in the fluids:
blood, lymph and interstitial fluid

Question 3

what do TCRs recognise?

Answer 3

antigenic fragments that have been processed and then presented by MHC molecules

Question 4

true or false, MHC binds self and non self

Answer 4

true, but T cells only respond to non-self

Question 5

how does one HLA gene complex code for so many different epitopes?

Answer 5

polymorphism: variation within sequences of genes within the population
polygenism: many genes expresses within an individual (we express 6 diff MHC I and 6 diff MHC II - one of the three from each parent)

Question 6

what is MHC restriction?

Answer 6

A T cell can only recognise its antigen when it is presented by its MHC molecule
- binds antigen-MHC complex, not just antigen

Question 7

what effect does polymorphism have on the MHC molecule

Answer 7

• differing structures of the MHC molecule (effects T cell binding) and the binding groove (effects antigen binding)

Question 8

describe MHC class I

Answer 8

• binds peptides made endogenously (inside the cell)
• bind to CD8+ cells which kill infected cells
• expressed on all nucleated cells (so not RBCs

Question 9

describe MHC I structure

Answer 9

• 3 alpha regions and one beta

Question 10

describe peptide loading for MHC class I

Answer 10

• high error rate in translation targets dysfunctional protein for proteolysis
• Ubiquitin binds dysfunctional protein, which targets it to the immuno-proteasome
• proteasome chops up protein
• protein fragments bind TAP 1 and TAP 2, which hydrolyses ATP and fragments enter the RER. then they bind MHC I and it follows secretory pathway without TAP 1 and 2

Question 11

what does TAP stand for in TAP 1 and 2?

Answer 11

transporter associated with
antigen
processing

Question 12

describe the immunoproteasome

Answer 12

in an inflammatory response the B1,2 and 5 subunits are replaced with immunospecific subunits B1i, B2i etc
- proteins cut to specific lengths for MHC 1

Question 13

describe unbound MHC in the RER

Answer 13

very unstable, so requires chaperones to stabilise and dock MHC close to the TAP complex

Question 14

how can viruses interefere with antigen presentation?

Answer 14

• can interfere with TAPs so proteins cant enter ER
• can retain MHC I in RER
• can force it to the lysosome
• downregulation of MHC at surface

Question 15

describe MHC class II

Answer 15

• binds peptides from exogenous proteins (proteins that have to be internalised)
• only found on specialised cells (APCs and B cells)
• recognise helper T cells

Question 16

describe peptide loading for MHC class II

Answer 16

• antigen is endocytosed and brought into the lysosome, where pH dependent unfolding happens
• the lysosome fuses with the endosome, where MHC II is
• peptides and MHC II is trafficked to cell surface, not yet bound
• invariant chain is cleaved into CLIP
• formation of HLA-DM removes CLIP and peptides bind to MHC II
• presentation

Question 17

what do invariant chains do?

Answer 17

they block the MHC II binding groove to prevent ER peptides from binding.

Question 18

what is cross-presentation?

Answer 18

when MHC class I loads an exogenous antigen which is not normal