MHC and Ag Presentation to T Cells- Lecture 7/8 Flashcards
(19 cards)
What is another name for naive T cells?
Th0
What kind of T cell expresses the CD4+ receptor and what is their function?
What are their 2 types and their functions?
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
What kind of T cell expresses the CD8+ receptor? What is their function?
Cytotoxic T cells
○ Associated with MHC class I ○ Fights intracellular pathogens
Where are T Cell Receptors (TCR’s) found?
Only on T cell membranes
What are TCR’s made up of?
Most are made of α and β chains
○ Constant region
○ Variable region (makeup Ag-binding site)
What binds to T Cell Receptors?
Can only bind PROCESSED PROTEIN AG
How are γδ T cells different from the regular TCR’s?
● 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
What are the 4 components of the TCR complex?
TCR (alpha and beta chains)
CD3
Zeta ( ζ) chain
CD4 or CD8
What is the purpose of CD3’s in the TCR complex?
○ 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
What is the purpose of the Zeta ( ζ) chain in the TCR complex?
Signaling complex
What is the purpose of CD4 or CD8 in the TCR complex?
These will bind to either MHC-II (CD4)
or MHC-I (CD8)
MHC Loci (Genes) has 2 types, MHC class I and MHC class II. Which genes are associated with each?
MHC class I
○ HLA-A
○ HLA-B
○ HLA-C
MHC class II
○ HLA-DQ
○ HLA-DR
○ HLA-DP
Each person gets___ HLA genes. How many from each parent and what does this allow for?
Each person gets six HLA genes
○ 3 from mom
○ 3 from dad
○ Allows the variation we see!
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?
● 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
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?
● 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
Describe the MHC class I processing pathway.
● 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
Describe the MHC class II processing pathway.
● 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
Describe how MHC class II pathway can cross over into the MHC class I pathway.
● 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
What are the 2 amino acids used for peptide binding recognition?
Leucine (L)
Tyrosine (Y)
