MHC molecules

Question	Answer
What blocks MHC class II presentation?	chloroquine and NH4Cl=prevents acidification and protease inhibitors
Describe the difference between immature and mature dendritic cells	immature has high intracellular MHC class II and are good at capturing Ag. Once the Ag has been captured, it becomes mature-MHC now on cell surface, SA increases, stops capturing and upregulation of accessory protein expression
What cytokine is responsible for the conversion into mature dendritic cell?	IL-10
What do MHC class I recognise?	CD8+ CTL T cells-detection of virus infected cell
What cells are MHC class I expressed on?	all nucleated cells
Describe the structure of the proteosome	core structure (20S proteosome)- 4 discs (2 alpha, 2 beta) made up of 7 subunits, 3 of beta subunits contain active sites. Regulatory (19S proteosome)
How does the proteosome degrade antigens into peptides?	proteins are targetted for degradation by ubiquitin. 19S then recognise this and unfolds them, they are then fed through the centre of core particle and degraded
In the MHC class I pathway, how do peptides get from the cytosol into the ER?	by TAP which is an ATP binding cassette family of transporters made up of TAP1 and TAP2 (heterodimer)-it forms a channel so peptides of 8-13AAs can go across ER membrane
How does MHC class I bind the peptide?	MHC heavy chains first associate with calnexin- heavy chain folds to form capable binding of beta 2 microglobulin. Calnexin is then replaced with calreticulin. TAPSIN and ERp57 then associates and generates PLC- MHC can then bind peptide and move to cell surface
Where is the peptide binding groove on MHC class I?	between alpha 1 and alpha 2
IN MHC class I processing how many AA do proteosomes generate/ TAP recognise/ MHC bind?	proteosome- ~5-15, TAP-8-13, MHC-9
Where are peptides trimmed down in the MHC class I pathway?	ER
What is the source of protein for MHC class I?	DRips, OAPs
What is cross presentation?	exogenous antigens can be taken up by dendritic cells by phagocytosis or they may find direct access across ER and then sec61 drives them back into cytosol where they are degraded by proteosome etc
How does a proteosome change into an immunoproteosome?	IFN-y produced when infected by virus causes 3 active site subunits to be replaced by LMP2, LMP7 and MECL-1 which changes the proteolytic specificity of proteosome to form immunoproteosome
where do antigens come from in the MHC class II pathway?	exogenous
Describe the MHC class II processing pathway of antigens into peptides?	exogenous antigen is captured into endocytic route by receptor mediated endocytosis. Proteolysis of the Ag then takes place in lysosomes/endosomes-acid pH initiates protein unfolding and then GILT(IFNy inducible lysosomal thiol reductase which catalyses disulphide bond breakage)
Name two lysosomal/endosomal proteases involved in MHC class II processing?	cathepsins and AEPs
What is MHC class II complexed with in the ER and what is it role?	the invariant chain which prevents peptide binding & chaperones class II to endosomal/lysosomal compartments where the chain is degraded into fragments by proteases- CLIP binds the MHC class II peptide groove
What is the role of HLA-DM? Describe its structure	in the presence of antigen peptide fragments, It binds MHC releasing CLIP and allowing peptides to bind. Glycoprotein consisting of alpha & beta chain encoded in MHC class II locus on ch 6
Describe CD4 molecules, MHC class II, helper T cells and TCR interactions	CD4 molecules on helper T cells recognise MHC class II heavy chains (a2 & b2). The TCR recognises the MHC/peptide complex
What is the MHC class II genes encoded by?	3 main alleles on ch 6= DP, DQ and DR
Describe the difference between TH1 and TH2 cells?	TH1 secretes IFN-y and IL-2 and enhances cellular immunity, TH2 secretes IL-4, IL-5 and IL-10 which enhances humoural response (Abs)

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	Created by tanitia.dooley almost 11 years ago