Lecture 8, Ag Presentation

Question 1

Name the immune cells that present class II MHC.
Which is/are not phagocytic?

Answer 1

DCs, macrophages, monocytes, B cells

- B cells are not phagocytic

Question 2

What are macrophages known as in the liver?

Answer 2

Kupffer cells

Question 3

What are macrophages known as in the brain?

Answer 3

Microglial cells

Question 4

What are DCs known as in the skin?

Answer 4

Langerhans’ cells (form a continuous cellular sheet at the junction of the dermis and epidermis)

Question 5

What are DCs known as in the T lymphocyte area of lymph nodes?

Answer 5

Interdigitating DCs

Question 6

What are DCs known as in the B lymphocyte area of lymph nodes?
Where else are these cells found? (1 place)

Answer 6

Follicular DCs

- Spleen as well

Question 7

Name the 2 main classes of DCs.

Answer 7

1. Plasmacytoid DC (we won’t focus on these much)

2. Conventional DC

Question 8

What do plasmacytoid DCs do?

Answer 8

Produce copious amounts of interferons (antiviral agents)

Question 9

What do conventional DCs do? (what we talk about in this class)

Answer 9

Phagocytosis, Ag-presentation, and trafficking to the regional lymph node.

Question 10

W/o naming proteins, generally describe class I MHC processing s/p viral infection. (also occurs for tumor cell)

Answer 10

• Viral protein infects cell
• Viral protein synthesized in the cytoplasm
• Peptide fragments of viral proteins bound to MHC class I in ER
• Bound peptides/MHC I xported to cell surface
• Presents to CD8+ T cells

Question 11

W/o naming proteins, generally describe class II MHC processing.

Answer 11

• Ag taken up into neutral endosome
• Endosomal acidification activates proteases, digest invading protein
• Fusion of this w/another vesicle containing MHC class II
• Presentation on cell surface to CD4+ T cells

Question 12

What 2 major proteins make up the proteasome?

Answer 12

LMP2 and LMP7

Question 13

Is the proteasome associated w/class I or II MHC processing?
Where is the proteasome located?

Answer 13

Class I (digests foreign peptides)
- Cytoplasm

Question 14

Although most of the time there is no foreign protein to digest by the proteasome, the cell still must present its MHC class I. What 2 things can be presented instead?

Answer 14

• Old proteins (70%)

- DRiPs (defective ribosomal particles, 30%)

Question 15

Where does MHC class I synthesis take place?

Answer 15

ER

Question 16

Prior to beta-2 microglobulin binding the MHC class I in the ER, what protein is bound to the partially folded MHC class I?

Answer 16

• Calnexin (a chaperone)

Question 17

Once beta-microglobulin binds the partially formed MHC class I protein to make a fully functional MHC class I in the ER, what chaperone changes occur?

Answer 17

• Calnexin leaves

- Calreticulin and ERp57 (chaperone complex) binds

Question 18

Still in the ER, the fully formed alpha-beta MHC class I is now bound to the calreticulin and ERp57 chaperone complex. This can then associate w/the protein ____________ via ___________.

Answer 18

TAP, via tapasin

TAP: transporter associated w/Ag processing

Question 19

Once the alpha-beta MHC class I is binding calreticulin, ERp57, and TAP (via tapasin), what does TAP do?

Answer 19

Delivers peptides that were digested by the proteasome (either from viral protein, normal protein, or DRiPs)
(TAP then releases the MHC class I to go to cell surface)

Question 20

What’s the name of the protein in the ER that cleaves proteins into smaller fragments after they’ve already been degraded by the proteasome but prior to their insertion into the MHC class I binding groove?

Answer 20

ERAAP

Question 21

Prior to MHC class II-containing endosomes binding w/phagolysosomes (containing digested foreign peptide), what important protein is associated w/the MHC class II molecules and why?

Answer 21

Invariant chain (Ii)
- Keeps self peptides/misfolded proteins out of the binding cleft

Question 22

In an endosome w/MHC class II and bound invariant chain, what is the next step that occurs?
What protein remains in the MHC's groove?

Answer 22

Acidification
- Invariant chain is fragmented, but a piece of it called CLIP (class II associated invariant peptide) remains in the groove

Question 23

Now we have an acidified endosome w/class-II MHC and CLIP bound to the binding groove. Once this endosome binds the phagolysosome, how can digested foreign Ag become incorporated into the MHC class II binding groove?

Answer 23

HLA-DM binds the class II HLA
(allows CLIP to cleave and foreign peptide to enter; MHC then travels to cell surface)

Question 24

(Not important) What protein serves as a negative regulator for HLA-DM?

Answer 24

DO (DOA and DOB)

Question 25

Generally speaking, what is the response of a CD4+ T cell once it binds specifically to an APC and is activated?

Answer 25

T cell proliferation and differentiation

Question 26

What are the 2 subsets of CD4+ T helper cells? | What is the general role of each?

Answer 26

- Th1: macrophage activation - Th2: B cell activation (-> AB synthesis) (To a lesser extent Th1 cells can also activate B cells to produce ABs)

Question 27

What APC or T cell interaction do B cells need to bind/recognize Ag?

Answer 27

Nothing, they can bind Ag directly (they are APCs)

Question 28

Generally, what do Th1 cells produce that activates macrophages? How does this change the macrophage?

Answer 28

Cytokines - Th1 cytokines make macrophages very active and helps them engulf and destroy some invaders that they otherwise wouldn't, such as mycobacterium tuberculosis

Question 29

Generally, what do Th1 cells produce that activates B cells? | How does this change the B cell?

Answer 29

``` Cytokines - Required for growth, class switching, differentiation into plasma cells, etc. ```

Question 30

Upon encountering Ag, an APC becomes highly active. Besides presenting Ag via MHC, what other receptor does the APC initially express?

Answer 30

B7

Question 31

Co-stimulation is required for an APC to activate a T cell. What receptor found on T cells must bind B7 of APCs?

Answer 31

CD28

Question 32

If an activated APC binds the MHC of a T cell, but said APC doesn't initially express B7 (to bind CD28 of T cell), how can B7 expression be stimulated in the APC?

Answer 32

- T cell is stimulated to make and express CD40 ligand (CD40L), which binds CD40 of APC. - This leads to APC's expression of B7

Question 33

What receptors are required for a Th2 (helper) cell to bind a B cell, differentiate it into a plasma cell, and secrete ABs?

Answer 33

- First MHC II binds TCR + B7 binds CD28 - Next T cell is stimulated to produce CD40L, binds CD40 - Cytokine receptors are produced on B cell, and cytokines are released by T cell

Question 34

The mechanisms of sustained TCR engagement to an APC is the formation of a specialized contact, termed the ________________________.

Answer 34

Immunological synapse

Question 35

What's the name of the outer ring of the immunological synapse? What general type of proteins are found here?

Answer 35

- pSMAC (peripheral) | - Adhesion molecules

Question 36

What's the name of the inner ring of the immunological synapse? What general type of proteins are found here?

Answer 36

- cSMAC (central) | - Signaling molecules

Question 37

Name the actual proteins found in the cSMAC (center of immunological synapse).

Answer 37

TCR, CD4, CD28, MHC:peptide, CD8, PKC-theta

Question 38

Name the actual proteins found in the pSMAC (periphery of immunological synapse).

Answer 38

LFA1-ICAM1, talin

Question 39

Name the 3 general steps that occur when an APC binds a T cell. - How are the different proteins arranged in each step.

Answer 39

1. Junction formation - Adhesion proteins toward the center 2. MHC-peptide transport - cSMAC proteins start to move to the center 3. Stablization - cSMAC in center, pSMAC in periphery

Question 40

What can CD8+ CTLs do after they bind their target cell?

Answer 40

Release cytolytic granules that can destroy their target

Question 41

``` MHC class I molecules under normal conditions (in the absence of foreign ag) are loaded with self peptides derived from the normal degradation of self cellular proteins. MHC class II molecules, under normal conditions, are thought to contain only _________ in their peptide binding groove. ```

Answer 41

CLIP

Question 42

What are the major differences b/w immature and mature DCs, in terms of phagocytosis, Ag presentation, and T cell activation? Do both produce B7?

Answer 42

- Resting (immature) APCs (e.g. DCs) are highly phagocytic but do not present Ag particularly well - S/p phagocytosis of an Ag, DCs mature and present Ag very well to T lymphocytes - Unlike immature DCs, mature DCs express on their surfaces large amounts of co-stimulatory molecules, e.g. B7 (also known as CD80 and CD86), and can also produce large quantities of cytokines required for T lymphocyte proliferation and differentiation.

Question 43

Generally, what happens to the T cell when it correctly binds its immunological synapse w/a DC?

Answer 43

T cell proliferates and differentiates

Question 44

According to the handout, what two processes require CD40/CD40L interaction? (not sure if it's needed in other situations as well).

Answer 44

1. T cell activation w/o presence of B7 on APC (induces B7) | 2. T cell activation of plasma cells to produce ABs