Lecture 4 - Dendritic cells

Question 1

Dendritic cells: what are they, what do they detect, how do they do their detection, what do they do, and where can they be found?

Answer 1

Professional antigen-presenting cells (APCs)

Danger - non-self antigens and/or inflammatory cytokines

Expresses PRRs

Take up antigen, process it, and display it for recognition by and activation of naive T cells

Can be found throughout the body but tend to be found in locations in lymph nodes where b and t cells reside

Question 2

Differences between immature and mature dendritic cells?

Answer 2

Immature:
* High endocytosis, phagocytosis, or macropinocytosis
* Lower MHC II
* Low costimulatory molecules
* Low adhesion molecules

Mature:
*Low endocytosis/phagocytosis
* High MHC II
* High costimulatory molecules
* High adhesion molecules

Question 3

Lymphoid tissues

Answer 3

rewatch leccy

Question 4

Dendritic cell variations

Answer 4

Multiple subsets in humans and mice

Question 5

pDCs: what are they, what do they do, are they good APCs, and where do they originate from?

Answer 5

Plasmacytoid DCs - potent antiviral cells - producers of type I interferons which promote NK and CD8+ T cell cytotoxicity and secretion of IFNγ

Less effective APC than conventional DCs

May originate from a different progenitor than other DCs (lymphoid as opposed to myeloid)

Question 6

Antigen uptake by dendritic cells: what are the three potential ways?

Answer 6

1) Receptor mediated endocytosis - cell surface transmembrane receptors which internalize into small clathrin coated pits

2) Macropinocytosis - non-clathrin associated, linked to membrane ruffling, where large volume is taken up into large vesicles

3) Phagocytosis - engulf and digest antigens via phagolysosome pathway

Question 7

Receptor mediated endocytosis: how does it work and what examples of families that detects substances that need to be endocytosed?

Answer 7

Cell surface transmembrane receptors which internalize into small (0.1µm) clathrin coated pits

• C-type lectin family, recognize glycosylated antigens - DEC205 (CD205), mannose receptor, DC-SIGN (binds HIV/ICAM-3)
• CD36 (recognizes apoptotic cells)

Question 8

Macropinocytosis: what is it and how often does it occur?

Answer 8

Non-clathrin associated (linked to membrane ruffling) intake of material - a large volume is taken up and forms large vesicles (~20µm) which effect to concentrate external macro-molecules by shrinking

Constitutive

Question 9

Phagocytosis: what is it, does the process benefit from antibodies, and what may occur with Fc opsonisation?

Answer 9

The internalisation of material, forming a phagosome which goes on to form a lysophagosome after fusion with lysosome(s) which can then kill any microbes

Yes antibodies can allow for opsonisations of macromolecules

FcRs present on DCs are receptive for IgE and IgG - Fc clustering may result in generation of larger phagosomes which may fuse with lysosomes

Question 10

Upon the recognition of “danger”, DCs rapidly mature

Answer 10

1. An initial short lived (30-45 mins.) “burst” of antigen capturing mechanisms followed by down modulation
   (levels of receptors reduced, changes in
   endocytosis, macropinocytosis, for example.)

Question 11

Maturation of dendritic cells

Answer 11

Migration away from site of antigen encounter to T cell areas.

Podosomes - F-actin rich structures found on ventral surface of DCs,
thought to be involved in cell migration

Question 11

How do DCs re-organize their class II?

Answer 11

Class II in immature DCs is held intracellular by a failure to
process Ii. (Inhibition of cathepsin S by expression of an
endogenous proteinase inhibitor, cystatin C).

Upon DC maturation cystatin C activity decreases, and class II/peptide complexes are formed and transport to the cell surface.
(Pierre and Mellman,Cell,1998)

or class II in immature DCs is simply rapidly internalized.
Upon maturation this rate is reduced by a global reduction
in endocytosis, hence more on surface.
(Villadangos et. al. 2001 Immunity 14, 739-)
(cystatin C knockouts: El-Sukkari et. al. 2003 J. Immunol, 171, 5003)

Question 12

CCR7 CCL21

Answer 12

Research

Answer 13

• alters DC dialogue with T cells to influence character of T cell response (Th1 vs. Th2 vs. Th17 vs. Treg etc.)
• TH1 - IFN-gamm - ??
• TH2 - IL-4/13 - Helminths/allergens
• TH17 - IL-17 - Antifungal/extracellular bacteria
• Tregs - IL-10/TGFB/RA - ???

Question 14

Dendritic cells and switchinmg T cells off

Answer 14

Research/leccy

Question 15

Is T-cell activation solely dependent on

Answer 15

T cell stimulation and polarisation requires 3 distinct signals

Resaesch/leccy

Question 16

What other cells do DCs interact with and how?

Answer 16

• CD8+ T cells via cross-presentation
• B cells via transport and exchange of in-tact antigen
• NK cells via IL-12 secretion, which stimulates NK IFNγ
• MØ via cytokine secretion (e.g. TNF)

Question 17

Macrophages vs DCs

Answer 17

• Embryonic origin
• Monocyte derived DCs (moDCs) (abundant during inflammation)…
  …vs conventionally derived DCs (cDC)

Question 18

Last slide

Answer 18

rewatch leccy