Lecture 9 - Dendritic Cells and Antigen Processing

Question 1

How is adaptive immunity triggered?

Answer 1

By capturing and presenting of foreign materials to cells that can recognize it

Question 2

What cells trigger adaptive immuntiy

Answer 2

antigen presenting cells

Question 3

3 major antigen presenting cells

Answer 3

1. Dendritic cells
2. Macrophages
3. B-cells

Question 4

What are APCs attracted by

Answer 4

microbial products and tissue damage and
are activated by the triggers of inflammation

Question 5

What is an advantage of DCs and macrophages also being sentinel cells

Answer 5

antigen processing can be rapidly initiated as body is responding to the microbial insult

Question 6

How do APCs capture foreign microbes and process them

Answer 6

process large proteins by breaking them into peptides and presenting on their surfaces attached to specialized antigen-presenting structures, called Major Histocompatibility Complex (MHCs)

Question 7

What are the only cells that can trigger naive T cells and what response do they trigger

Answer 7

dendritic cells, primary immune response

Question 8

Dendritic cells

Answer 8

special APCs that are especially important in activating a naïve T cell and triggering a primary response

Question 9

B cells

Answer 9

Present antigen to memory TH cells

Question 10

Macrophages

Answer 10

Present antigen to memory TH cells

Question 11

DCs are primarily present in

Answer 11

epithelial tissues (skin, mucosa) and in lymphoid organs (lymph nodes, spleen, thymus

Question 12

Major functions of dendritic cells

Answer 12

1. Serve as sentinel cells - activate innate defenses
2. Process exogenous antigens - initiate adaptive immune system
3. Regulate adaptive immunity

Question 13

How much more efficiient are DCs as APCs

Answer 13

100x

Question 14

What can DCs take up

Answer 14

dead microorganisms, soluble antigens, antigen
released by dead cells, etc.

Question 15

How are follicular dendritic cells different from other DCs

Answer 15

I. do not migrate
II. are located in lymphoid follicles (B-cell area)
III. lack MHC II molecules on their surface
IV. carry many complement and Fc receptors

Question 16

How long can FDCs retain antigen

Answer 16

many weeks

Question 17

T/F FDCs process antigens

Answer 17

FALSE

Question 18

Primary function of FDCs

Answer 18

present antigen to B cells

Question 19

What FDC look like

Answer 19

octopus with a large number of tentacles! The “tentacles” are beaded dendrites.

Question 20

Beads on FDCs are …

Answer 20

antigen:antibody complexes that have attached to the dendrites via complement and Fc receptors

Question 21

Immune complexes on FDCs form

Answer 21

spherical bodies called iccosomes

Question 22

What happens when iccosomes break off from dendrites

Answer 22

attach to B cells

Question 23

What happens after iccosomes attach to B cells

Answer 23

ingested by activated B cells with BCRs specific for antigen, antigen processed, B cell presents antigen on MHC II molecules to activated TH cell

Question 24

Macropinocytosis

Answer 24

DCs in epithelium take in extracellular fluid to sample for signs of pathogens and their products

Question 25

What do DCs do after they pickup antigens from site of infection

Answer 25

take them to environment full of immune cells

Question 26

What happens after activated DCs stop phagocytosis

Answer 26

move into the interstitial space, and are carried by lymph flow to the nearest lymph node

Question 27

When do DCs move to lymph node

Answer 27

when infection is underway, stimulated by inflammatory cytokine TNF-a

Question 28

During migration of activated DCs, expression of ____ and ____ are upregulated

Answer 28

MHC II and B7

Question 29

_____ containing digested antigens will fuse with endosomes containing _______ molecules

Answer 29

Phagolysosomes; MHC II

Question 30

___ are loaded on to the MHC II molecules and eventually reach the cell surface where they can be presented to ______________

Answer 30

Peptides; T cells

Question 31

When the activated DCs arrive in the lymph node, _____ cells scan the large array of loaded peptides for their _____.

Answer 31

TH, cognate antigen

Question 32

Activated DCs in lymph nodes express ____ times more MHC II molecules than any other APC

Answer 32

100

Question 33

One activated DC can activate up to ____ T cells

Answer 33

3000

Question 34

When DCs stimulate T helper cells, they provide three signals:

Answer 34

1. T cell antigen receptors bind antigen fragments attached to MHC molecules.
2. Co-stimulatory molecules like CD40 and CD80/86.
3. Provided by cytokine secreted by DCs in response to microbial stimulus

Question 35

What are NOT efficient APCs

Answer 35

macrophages

Question 36

Why are macrophages not good APCs in the resting stage

Answer 36

do not express adequate levels of MHC II and/or co-stimulatory molecules

Question 37

When can macrophages function as APCs

Answer 37

when activated by cytokines, such as INFγ, their expression of MHC II and co-stimulatory molecules are up-regulated

Question 38

Why are naive B cells not good APCs

Answer 38

do not express the co-stimulatory B7 molecule needed for T-cell activation and also express low levels of MHC II molecules

Question 39

When do B cells become efficient APCs

Answer 39

once activated by T helper cells

Question 40

Activated B cells upregulate ___ and ___, and become potent activators of ____

Answer 40

MHC II; co-stimulatory B7; T helper cells

Question 41

What immune response do B cells play a more significant role as APCs

Answer 41

SECONDARY

Question 42

What are the only cells that can effectively stimulate naive T cells

Answer 42

DC

Question 43

Dendritic cells express a high level of what antigen receptors on their surface

Answer 43

MHC II

Question 44

How do DCs help T cells recognize antigens

Answer 44

DC ingest, fragment antigens, present them to surface MHC, recognized by TH cells