Lec5 Antigen Capture and Processing

Question 1

What form of antigen do T cells recognize?

Answer 1

antigen as peptide presented on pAPC with MHC

Question 2

Do T cells recognize free antigens?

Answer 2

No!

Question 3

What makes pAPC unique?

Answer 3

• express MHC class I AND class II

- only cells capable of activating naive T cells

Question 4

What is most effective cell at activating naive T cells?

Answer 4

Dendritic cell

Question 5

What are three types of pAPC

Answer 5

• dendritic cells
• macrophages
• B cells

Question 6

Is MHC always on cell surface even in non-infected cells?

Answer 6

Yes - with self-protein

Question 7

What is most polymorphic genetic system known?

Answer 7

MHC molecules

Question 8

2 Reasons for diversity in MHC

Answer 8

• number of different genes

- variety of alleles [alternate forms] for eah gene

Question 9

Structure of MHC Class I Molecules

Answer 9

• 1 alpha wtih 3 domains: contains binding pocket
• 1 beta [beta microglobulin
  only one transmembrane region

Question 10

Structure of MHC Class II Molecules

Answer 10

• 1 alpha with 2 domains
• 1 Beta with 2 domains
• binding pocket = a1 and b1
  two transmembrane eregions

Question 11

What does MHC need to bind cell surface stably?

Answer 11

Needs to bind peptide first

If not it will come off before T cell has time to see it

Question 12

What is DM?

Answer 12

• 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

Question 13

What is TAP? What MHC and T cell associated?

Answer 13

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]

Question 14

What cells express MHC Class I? Present cytosolic or external proteins? Present to what type of T cell?

Answer 14

• expressed on most nucleated cells
• present cytosolic proteins
• to CD8 T cells

Question 15

What cells express MHC Class II? Present cytosolic or external proteins? Present to what type of T cell?

Answer 15

• expressed on pAPCs: macrophages, B cells, active T cells
• present external proteins
• to CD4 T cells

Question 16

What is significance of Co-dominant expression of MHC? What does it mean?

Answer 16

• 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

Question 17

What part of MHC is variable? What function does this allow?

Answer 17

• the part in the peptide binding cleft

- allows it to bind different peptides

Question 18

Exogenous pathway of antigen processing? What type of MHC? What type of T cell?

Answer 18

• 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

Question 19

Endogenous pathway of antigen processing? What type of MHC? What type of T cell?

Answer 19

• 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

Question 20

Endogenous or exogenous for viruses?

Answer 20

Endogeneous

Question 21

Are viruses or bacteria process via exogenous pathway?

Answer 21

bacteria

Question 22

What is CLIP? Functions with what type of MHC and T cell?

Answer 22

• 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

Question 23

What is cross-presentation?

Answer 23

• 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