MHC and Ag Presentation to T Cells- Lecture 7/8

Question 1

What is another name for naive T cells?

Answer 1

Th0

Question 2

What kind of T cell expresses the CD4+ receptor and what is their function?

What are their 2 types and their functions?

Answer 2

helper T cells

Recognize Ags on MHC II on APCs
○ Th1 = intracellular pathogens, produce IFN-γ (activate Mφ)
○ Th2 = extracellular pathogens, help develop B cell to memory cells

Question 3

What kind of T cell expresses the CD8+ receptor? What is their function?

Answer 3

Cytotoxic T cells

○ Associated with MHC class I
○ Fights intracellular pathogens

Question 4

Where are T Cell Receptors (TCR’s) found?

Answer 4

Only on T cell membranes

Question 5

What are TCR’s made up of?

Answer 5

Most are made of α and β chains
○ Constant region
○ Variable region (makeup Ag-binding site)

Question 6

What binds to T Cell Receptors?

Answer 6

Can only bind PROCESSED PROTEIN AG

Question 7

How are γδ T cells different from the regular TCR’s?

Answer 7

● Small percentage of T cells
● Made of γ and δ chains
● Much wider specificity (don’t have to bind proteins only)
○ Eg HSPs and phospholipids

Question 8

What are the 4 components of the TCR complex?

Answer 8

TCR (alpha and beta chains)
CD3
Zeta ( ζ) chain
CD4 or CD8

Question 9

What is the purpose of CD3’s in the TCR complex?

Answer 9

○ This is on ALL T Cells
○ Can be used as a diagnostic tool to
find T cells
○ Sends signals into T cell → production
and release of cytokines

Question 10

What is the purpose of the Zeta ( ζ) chain in the TCR complex?

Answer 10

Signaling complex

Question 11

What is the purpose of CD4 or CD8 in the TCR complex?

Answer 11

These will bind to either MHC-II (CD4)

or MHC-I (CD8)

Question 12

MHC Loci (Genes) has 2 types, MHC class I and MHC class II. Which genes are associated with each?

Answer 12

MHC class I
○ HLA-A
○ HLA-B
○ HLA-C

MHC class II
○ HLA-DQ
○ HLA-DR
○ HLA-DP

Question 13

Each person gets___ HLA genes. How many from each parent and what does this allow for?

Answer 13

Each person gets six HLA genes
○ 3 from mom
○ 3 from dad
○ Allows the variation we see!

Question 14

Describe MHC class I receptors.

Where are they found?
What kind and how many chains does it have?
What special protein does it contain?
What kinds of peptides does it bind?
What enhances its expression?
What kind of T cells does it bind to and what part of the T cell does it bind to?
Does this deal with intracellular or extracellular pathogens?

Answer 14

● On all nucleated cells (so no RBCs)
● Contains one α chain
● CONTAINS β-MICROGLOBULIN
● Binds short linear peptides
● Enhanced expression with IFNγ and IFNα/β
● Binds to CD8 T cells (binds to α chain)
● Deals with intracellular pathogens

Question 15

Describe MHC class II receptors.

Where are they found?
What kind and how many chains does it have?
What kinds of peptides does it bind?
What enhances its expression?
What kind of T cells does it bind to and what part of the T cell does it bind to?
Does this deal with intracellar or extracellular peptides?

Answer 15

● Expressed on professional APCs
○ B cells, DCs, Mφ
● Two chains (α and β chains)
○ Different than chains on TCR
● Bind to short linear peptides (longer
compared to MHC-I)
● Enhanced expression under IFN-γ
● Presents to CD4 T cells (binds to β chain)
● Usually extracellular peptides

Question 16

Describe the MHC class I processing pathway.

Answer 16

● Virus peptides are tagged by ubiquinase
○ Sent to proteasome for degradation
● TAP
○ This takes peptide fragments to ER
● MHC-I is created in ER
○ Meets up and binds with peptides
● MHC-1:Ag

Question 17

Describe the MHC class II processing pathway.

Answer 17

● Extracellular proteins (pathogenic) taken in via endocytosis
○ Fuses with lysosome = phagolysosome
● MHC-II made in ER, processed by GA, and processed in exocytotic
vesicle
● MHC-II vesicle fuses with phagolysosome
● CLIP
○ In vesicle this binds MHC-II so
nothing else binds
● HLA-DM
○ Removes CLIP
○ Stabilizes binding of peptide to
MHC-II
● Sent to membrane

Question 18

Describe how MHC class II pathway can cross over into the MHC class I pathway.

Answer 18

● Sometimes EC pathogens brought in via endocytosis leak into cytoplasm
● Get tagged by Ub
● Once tagged by Ub → goes through MHC-I pathway
● Results in EC pathogens presented on MHC-I to be bound by CD8+ T cells

Question 19

What are the 2 amino acids used for peptide binding recognition?

Answer 19

Leucine (L)

Tyrosine (Y)