Antigen presentation

Question 1

Which are the only APCs that can activate naive T-cells?

Answer 1

Dendritic cells

Question 2

Which are the 3 “professional” APC’s?

Answer 2

Dendritic cells, macrophages, B cells

Question 3

If a virus has infected a cell, will its proteins show up on the MHC I or MHC II?

Answer 3

MHC I (because the proteins are INSIDE the cell)

Question 4

Once proteins are cleaved by proteasomes, they are carried by the transporter proteins _____ and _____ into the ______ where they are loaded onto the grooves of class I MHC molecules

Answer 4

TAP1; TAP2; Endoplasmic reticulum (ER)

Question 5

What are the 3 major steps of preparing an MHC I display?

Answer 5

1. Cleavage of proteins by proteosomes
2. Transport onto ER by TAP transporter
3. Binding of peptide onto groove of MHC I molecule

Question 6

In activated APCs, proteasomes preferentially cut after hydrophobic or basic amino acids. Why is this important?

Answer 6

TAP and MHC I both prefer peptides with hydrophobic or basic C-termini, so this increases efficiency of MHC class I display

Question 7

Aside from transporting proteins to the ER, what other important functions do TAP transporters serve?

Answer 7

Sorting cleaved peptides by appropriate size and terminus properties (basic, hydrophobic)

Question 8

Which MHC class presents to T Helper Cells?

Answer 8

MHC II

Question 9

Whic MHC class presents to Cytotoxic T cells?

Answer 9

MHC I

Question 10

While _____ molecules are expressed on almost every kind of cell on the body, _____ molecules are expressed exclusively on immune cells

Answer 10

MHC I; MHC II

Question 11

Why is it important that the invariant chain of MHC II prevents the molecule from picking up peptides from the ER?

Answer 11

If the ER could load peptides onto MHC II, it would end up with many of the same peptides as MHC I (proteins from inside the cell)

Question 12

MHC I molecules are loaded with peptides from the ER; MHC II molecules are loaded with peptides from _______.

Answer 12

endosomes

Question 13

What are the two major functions of the invariant chains on MHC II molecules?

Answer 13

1. Block peptide loading by ER

2. Guide MHC II molecules to endosomes for peptide loading

Question 14

Once in the endosome, and much of the invariant chain has been cleaved off MHC II, a cellular protein called ____ catalyzes the release of the remaining fragment of the invariant chain (known as _____), allowing an exogenous peptide to be loaded into the now empty groove of MHC II

Answer 14

HLA-DM; CLIP

Question 15

Why is it important that MHC I and MHC II have separate loading sites and pathways?

Answer 15

Because they present different antigens (intracellular and extracellular) that are targeted by different lymphocytes (Cytotoxic vs Helper T cells). You don’t want to kill your own cells for an extracellular infection!!

Question 16

Co-stimulation of T cells usually involves a protein called ____ on the surface of an APC that inserts into a protein called ____ on the surface of a T cell

Answer 16

B7; CD28

Question 17

All APC’s must be _____ before they can present antigen to T cells

Answer 17

activated

Question 18

Name 2 ways in which a dendritic cell can be activated

Answer 18

TNFa; recognition of a DAMP or PAMP by a TLR

Question 19

Which Toll-Like Receptor recognizes LPS?

Answer 19

TLR4

Question 20

What are the two most important features of the patterns recognized by TLRs?

Answer 20

1. Recognize characteristics of classes of invaders - not individuals
2. Recognize structures or traits not easily altered by mutation

Question 21

TLR7 recognizes _______ RNA in viruses such as flu, and TLR9 recognizes ______ DNA in bacteria or herpes virus

Answer 21

single-stranded; double-stranded