Antigen Processing

Question 1

What happens if I mix an E. coli bacterium and a macrophage?

Answer 1

1. binding
2. engulfment
3. Phagosome formation
   Acidification via Respiratory Burst
4. Phagosome fuses with Lysosome to form Phagolysosome
   Digestion
5. Membrane Disruption

Question 2

The process of taking up a microbe, processing the antigens, and presenting it to a naïve T cell is what we refer to as

Answer 2

antigen processing and presentation.

Question 3

Dendritic Cells

Answer 3

Phagocytic cells

Question 4

Dendritic Cells: Minor population in the

Answer 4

blood, but:

found in skin, mucosa, lymph nodes, spleen, thymus

Question 5

Dendritic Cells: typically express

Answer 5

MHC II molecules

Question 6

Dendritic Cells: internalize and process

Answer 6

Ag

Question 7

Dendritic Cells: present

Answer 7

Ag peptides within MHC II on surface

Question 8

Dendritic Cells: important for presenting

Answer 8

Ag to T cells

Question 9

Dendritic Cells: important for activating

Answer 9

T cells

Question 10

Dendritic cells: PRIMARY

Answer 10

ANTIGEN-PRESENTIG CELL (Professional APC)

link between innate and adaptive immunity

Question 11

2. Monocytes/Macrophages: monocyte in blood —>

Answer 11

macrophage in tissue
5-10% of blood leukocytes
phagocytic cells

Question 12

2. Monocytes/Macrophages: characteristic

Answer 12

large nucleus

Question 13

2. Monocytes/Macrophages: very large

Answer 13

cell, 10 - 20 µm in diameter

Question 14

2. Monocytes/Macrophages: produce

Answer 14

chemotactic agents for other leukocytes

Question 15

2. Monocytes/Macrophages: contain arsenal of

Answer 15

lysozymes and antimicrobial proteins

Question 16

2. Monocytes/Macrophages: phagocytose

Answer 16

microorganisms, particles, & tumor cells

Question 17

2. Monocytes/Macrophages: extremely important for clearance of

Answer 17

dead cells & debris

Question 18

Monocytes/macrophages: extremely important for

Answer 18

antigen presentation

Question 19

B cells : a lymphocyte (part of adaptive immunity)

relatively

Answer 19

small, 6 - 10 µm in diameter

Question 20

B cells : produce

Answer 20

chemotactic agents to attract other leukocytes

produce cytokines to activate or inactivate other leukocytes

Question 21

B cells : can activate

Answer 21

T cells (more common in secondary (or memory) immune responses

Question 22

Antigen presentation is a way to

Answer 22

concentrate the antigen in areas most likely to come into contact with T cells and B cells.

Question 23

Antigen presenting cells are not limited to

Answer 23

dendritic cells, macrophages, and B cells.

Question 24

All nucleated cells can

Answer 24

present endogenous antigens in association with MHC I molecules

Question 25

What is the Major Histocompatability Complex (MHC)?

Answer 25

- Original function was linked only to graft rejection | - Later found to be of critical importance to all immune responses involving protein antigens

Question 26

MHC I

Answer 26

Found on all nucleated cells Cytoplasmic protein can be bound to MHCI Recognized by CD8+ T cells

Question 27

MHC II

Answer 27

Found on antigen presenting cells Extracellular proteins will be bound to MHCII Recognized by CD4+ T cells

Question 28

MHC II

Answer 28

Found on antigen presenting cells Extracellular proteins will be bound to MHCII Recognized by CD4+ T cells

Question 29

Antigen processing is the processes by which antigens are

Answer 29

digested and placed on the cell surface with the correct MHC molecule.

Question 30

Two pathways of antigen processing:

Answer 30

Extracellular proteins that are internalized by professional APCs into vesicles are processed and displayed by class II MHC molecules. Proteins in the cytosol of nucleated cells are processed and displayed by class I MHC molecules.

Question 31

Often the cytosolic proteins are

Answer 31

viral proteins.

Question 32

Virus enters into cell, process of

Answer 32

uncoating, replication, reassembly, release.

Question 33

During entry/uncoating and reassembly there are

Answer 33

viral proteins in cytoplasm.

Question 34

Proteins in the cytoplasm that are not used by the

Answer 34

cell get tagged for degradation.

Question 35

Ubiquitin binds to the

Answer 35

proteins which targets them to the proteosome.

Question 36

Step 2: Ubiquinated proteins are cleaved into

Answer 36

smaller peptides by the proteosome

Question 37

Step 3: Peptides are transported into the

Answer 37

endoplasmic reticulum through the TAP transporters (TAP stands for transporter associated with antigen processing)

Question 38

Step 4: As the peptide is being processed, Class I MHC molecule is being formed in the

Answer 38

endoplasmic reticulum.

Question 39

MHCI is unstable. Peptide binding in the binding groove will

Answer 39

stabilize the MHCI. If no peptide, the MHCI degrades

Question 40

Step 4: Peptide that is transferred into the ER by TAP is

Answer 40

trimmed to the correct size by an aminopeptidase called ERAP.

Question 41

The correct size peptide can then bind to the

Answer 41

binding groove of MHCI.

Question 42

Step 5: Once the MHCI binds to antigen, it is released from

Answer 42

ER (i.e., it is no longer bound to tapasin). The complex is packaged into a vesicle in the Golgi. Vesicle is trafficked to the cell surface, fused with the cell membrane resulting in expression of MHCI+Ag

Question 43

The antigen bound to MHCI can be a

Answer 43

foreign protein/peptide or it can be a self peptide (i.e., from a protein from the host cell). This is one way in which the immune system is supposed to recognize self vs. non-self.

Question 44

Antigen presentation bridges antigen recognition by

Answer 44

innate immune system to the activation of the adaptive immune system.

Question 45

Antigen presentation is necessary for

Answer 45

T cell-mediated killing, and augments antibody production by B cells.

Question 46

Antigen presentation is

Answer 46

context dependent, allowing the deployment of appropriate immune responses under different conditions.

Question 47

CD8+ T cells are

Answer 47

MHC I restricted and recognize cytosolic proteins

Question 48

CD4+ T cells are

Answer 48

MHC II restricted and recognize extracellular and intravesicular pathogens

Question 49

Multiple receptors on T cells need to be engaged in order to

Answer 49

activate the T cell. Recognition of antigen is not enough.

Question 50

The T cell receptor (TCR) recognizes antigen, but it does not

Answer 50

signal.

Question 51

CD3 and z are non-covalently associated to the

Answer 51

TCR Expression of the TCR, CD3 and z chain are required for antigen recognition and signalling TCR recognizes Ag CD3 and z signal

Question 52

Recognition of antigen (and MHC molecule) in the absence of

Answer 52

co-stimulation fails to activate the T cell. In fact, it leads to anergy of the T cell.

Question 53

Multiple receptors on T cells need to be engaged in order to activate the T cell. Recognition of antigen is not enough.

Answer 53

TCR recognizing antigen CD4 recognizing MHCII CD28 on T cell recognizing B7 molecules on APC LFA-1 on T cell recognizing ICAM-1 on APC Together they are referred to as the immunological synapse

Question 54

Self/Non-self vs. danger

Answer 54

Bacterial products such as those in the adjuvant stimulate the expression of MHC, adhesion molecules, and co-stimulatory molecules in APCs These signals provide T cells with “context” information that may determine the modality of their responses, e,g., tolerance, TH1, or TH2 response

Question 55

Function of co-stimulatory molecules | : Absence of

Answer 55

co-stimulatory molecules, T cell will not be activated (anergy)

Question 56

Function of co-stimulatory molecules | Absence of antigen-TCR interaction, T cell will not be

Answer 56

stimulated.

Question 57

Function of co-stimulatory molecules | Co-reception of

Answer 57

both signals activate T cells

Question 58

Function of co-stimulatory molecules | At the termination of the

Answer 58

immune response, CTLA-4 replaces CD28 and downregulates T cell function

Question 59

B7 Receptors Play a Role in

Answer 59

Activating T cells AND Terminating the T cell Response!!

Question 60

A. CTLA-4 can competitively inhibit

Answer 60

CD28 binding to B7

Question 61

B. CTLA-4, when bound to B7, will actively

Answer 61

block signals from the TCR and from CD28