Lec5 Antigen Capture and Processing Flashcards
What form of antigen do T cells recognize?
antigen as peptide presented on pAPC with MHC
Do T cells recognize free antigens?
No!
What makes pAPC unique?
- express MHC class I AND class II
- only cells capable of activating naive T cells
What is most effective cell at activating naive T cells?
Dendritic cell
What are three types of pAPC
- dendritic cells
- macrophages
- B cells
Is MHC always on cell surface even in non-infected cells?
Yes - with self-protein
What is most polymorphic genetic system known?
MHC molecules
2 Reasons for diversity in MHC
- number of different genes
- variety of alleles [alternate forms] for eah gene
Structure of MHC Class I Molecules
- 1 alpha wtih 3 domains: contains binding pocket
- 1 beta [beta microglobulin
only one transmembrane region
Structure of MHC Class II Molecules
- 1 alpha with 2 domains
- 1 Beta with 2 domains
- binding pocket = a1 and b1
two transmembrane eregions
What does MHC need to bind cell surface stably?
Needs to bind peptide first
If not it will come off before T cell has time to see it
What is DM?
- Intracellular protein involved in peptide presentation by MHC class II
- in endosomes promotes dissociated of CLIP [place holder peptide] from MHC class II to allow MHC to bind antigen
- MHC Class II, CD4
What is TAP? What MHC and T cell associated?
Transporter associated with antigen processing [TAP]
- aids in peptide translocation from cytosol into ER in endogenous pathway
- needed for antigen - MHC class I interaction [CD8]
What cells express MHC Class I? Present cytosolic or external proteins? Present to what type of T cell?
- expressed on most nucleated cells
- present cytosolic proteins
- to CD8 T cells
What cells express MHC Class II? Present cytosolic or external proteins? Present to what type of T cell?
- expressed on pAPCs: macrophages, B cells, active T cells
- present external proteins
- to CD4 T cells
What is significance of Co-dominant expression of MHC? What does it mean?
- we inherit 3 class I and 3 class II molec from each parent
- both parental alleles of each MHC are expressed
- increases number of different MHC molec that can present peptides to T cells
What part of MHC is variable? What function does this allow?
- the part in the peptide binding cleft
- allows it to bind different peptides
Exogenous pathway of antigen processing? What type of MHC? What type of T cell?
- for pathogens that come from outside of cells
- ex. extraecllular bacteria
- uptake extracellular protein and proces in endosome
- class II MHC molec interact with antigen in endosome
- peptide-MHC complex expressed on cell surface for CD4 T cells
- involves CLIP, DM
Endogenous pathway of antigen processing? What type of MHC? What type of T cell?
- for pathogens that replicate within cell
- ex. viruses
- transport peptides from cytosol to ER
- assembly MHC class I - peptide complex
- Express MHC class I and peptide on cell surface to CD8 T cell
Endogenous or exogenous for viruses?
Endogeneous
Are viruses or bacteria process via exogenous pathway?
bacteria
What is CLIP? Functions with what type of MHC and T cell?
- Class II associated invariant chain peptide
- binds MHC to prevent binding of self-peptide fragments prior to MHC localization to endosome
- in presence of antigen peptide, releases MHC to allow MHC to bind
- CD4
What is cross-presentation?
- APC takes up exongeous antigen but antigen goes into cytosol and undergoes endogenous pathway
- presents MHC Class I to CD8 [CTL]
- allows presentation of exogenous antigens that are normally presented by MHC II by MHC I
