19 - T cells II: CTLs & cytokine patterns

Question 1

Fas ligand & CD40 ligand Both expressed on

Answer 1

effector T cell surface
o Not expressed on naïve T cell

Question 2

Ligands = crucial for

Answer 2

effector T cell function

Question 3

Fas ligand & CD40 ligand are…. ligands, part of what family

Answer 3

Transmembrane ligands
TNF family

Cell-to-cell interaction
-CD40 ligand interact with CD40 on DC

Question 4

Fas ligand: Expressed on

Answer 4

surface of effector CD8+ & TH1 cell

Used by CD8+ T cell  cytotoxic effect

Question 5

what does Fas ligand do?

Answer 5

Bind Fas on surface of infected cells in periphery (site of infection)

Question 6

CD40 ligand, Expressed on

Answer 6

helpter T cells: TH1, TH2, TH17 & TFH cells

Question 7

CD40 ligand bind to

Answer 7

o Binds CD40 on B cells & innate immune cells (DC)

Question 8

CD40 ligand function:

Answer 8

o Used to activate target cells
o Allow for DC licensing (cross-presentation) & expression of more co-stimulatory molecules

Question 9

naive CD8+ T cells become…

Answer 9

Cytotoxic T Lymphocytes

Question 10

3 signals to activate CD8+ T cell

Answer 10

o Signal 1: TCR binds peptide presented by APC on MHC class I

o Signal 2: costimulatory signal transmitted by CD28-B7 (CD80/86) interaction between T cell and APC

o Signal 3: provided mainly by IL-2 & other cytokines (IL-12)  induce proliferation & differentiation into CTL form

Question 11

CD8+ specific considerations (4)

Answer 11

CD8+ cells require more co-stimulatory

IL-2 can be:
 Autocrine
 Paracrine from TH1 & TH17 cell

Require help of effector CD4 + T cells

Question 12

Once CD8+ T cells receive all signals = CTLs, what do CTLs do?

Answer 12

CTLs recognize & kill infected/tumour cells by recognition with their TCR

Question 13

CD8+ T cells can be activated in different ways to become CTLs (2)

Answer 13

Simplest & rarely:
-By activated DC that have high co-stimulatory activity (In some viral infections, DC becomes infected & sufficiently activated)
-it is rare because: virus don’t just infect any type of cell, Each virus has specific host cell & most don’t infect DC

Majority:
-Additional help with CD4 effector T cells & licensing DC to cross present

Question 14

2 models to activating CD8+ T cells:

Answer 14

sequential & SIMULTANEOUSLY

Question 15

Sequential

Answer 15

CD4+ T cell activated –> give permission through CD40 ligand binding –> activated CD8+ T cell

APC becomes further licensed following interaction with CD4+ cell
-Key part of licensing = signal APC receives through CD40 signaling

Interacts with CD8+ T cell independently

IL-2 produced by CD8+ T cells alone= induce proliferation (Autocrine fashion)

Question 16

Simultaneous

Answer 16

CD4+ T cell activated –> effector T cell –> CD40 signaling –> DC licensing

APC interacts with both CD4+ and CD8+ T cells at same time
-A moment in time, the DC interact with both CD4+ & CD8+ T cell
-By chance

Important: CD40 signaling due to interaction with CD40L on CD4+ t cell

IL-2 secreted by both CD4+ & CD8+ T cell -> induce proliferation of CD8+ T cell (paracrine fashion)

Question 17

CD40 signaling lead to …

Answer 17

DC licensing to cross-present& expression of more co-stimulatory molecules

Question 18

What needs to happen to CD4+ T cells to activate CD8+ T cells?

Answer 18

o Find its p:MHC class II match
o All 3 signals received
o CD40 ligand gets expressed & binds to CD40 on APC

Question 19

What needs to happen to DCs to allow them to present antigen to both CD4+ & CD8+ T cells?

Answer 19

o Encounter a PAMP
o Travels to secondary lymphoid organ (lymph node) as a mature DC
o Present antigen on MHC class II to CD43+ T cell
o Gets licensed through CD40 binding
o Presents antigen (from exogenous origin) on MHC class I to CD8+ T cell cross presentation

Question 20

Activation of CD4+ T cell:

APC licensed by activated CD4+ T cells through CD40 binding:

Answer 20

o IL-2 secretion
o CD40L expression

o Presenting exogenous antigen via MHC class II
o Cross-presentation to present antigen via MHC class I
o Increased expression of CD80/86
o Induction of additional molecule that activates CD8+ T cells
-4-1BBL (bind to 4-1BB) & CD70(bind to CD27)
——-Provide costimulatory molecules along with B7
o Increased production of IL-12

Question 21

CTL-mediated killing

Answer 21

Naïve CD8+ T cell (CTL precursors) gets activated & differentiates into CTL

CTL leaves lymph node -> travels to site of infection

CTL can kill infected cells in the periphery
-Interaction of TCR (+CD8 co-receptor) with pMHC class I

Question 22

… cells express MHC class I

Answer 22

All nucleated

Question 23

1. Initial interaction via

Answer 23

nonspecific adhesion molecules

Question 24

2. If pMHC isn’t a match

Answer 24

CTL moves on

Question 25

3. When CTL recognizes pMHC (an infected/cancerous cell)

Answer 25

4. Death of infected cell

Question 26

how does CTL Induce apoptosis to kill infected cells? (2)

Answer 26

o Fas-FasL mediated killing o Granules-mediated killing CTL also Secrete cytokines  direct immune response

Question 27

Fas-FasL mediated killing

Answer 27

Effector CTL expresses FasL Infected cells express Fas Signaling cascade: cleavage of pro-caspases -->caspases -->apoptosis of target cell

Question 28

Granules-mediated killing

Answer 28

CTL makes contact to target cell via nonspecific adhesion Specific recognition via TCR:pMHC Reorganization of cytoskeleton & cytoplasmic contents (granules & microtubules…) Granules released at point of cell contact

Question 29

Granules of CTLs (cytotoxins)

Answer 29

perforin deliver granzyme B

Question 30

perforin role:

Answer 30

Aids in delivering contents of granules into cytoplasm of target cells Delivers content of granules through forming pores Form pores to let granzyme pass through cell

Question 31

Granzymes – granzyme B role:

Answer 31

Serine proteases: activate apoptosis once in cytoplasm of target cell

Question 32

Granzyme/perforin-mediated cytolysis

Answer 32

When stimulated  CTLs release granule contents -Perforin = pore-forming proteins -Granzymes = serine proteases Perforin punches holes in membranes & granzyme enters to induce apoptosis

Question 33

steps in Granzyme/perforin-mediated cytolysis

Answer 33

TCR on CTL binds pMHC --> triggers intracellular signaling --> reorganization of intracellular structure & granule release --> perforin forms pores --> granzyme B enters cytoplasm of target cell --> initiates signaling through pro-caspases cleavage into caspases+other factors --> DNA fragmentation & cell death

Question 34

Membrane blebbing:

Answer 34

cytoskeleton break & causes membrane to bulge outward -Classic sign of apoptosis

Question 35

Cell-mediated effector responses

Answer 35

CTLs recognize & kill infected/tumor cells via TCR activation: -Perforin/granzyme pathways Fast-acting Primarily used by CTLs -Fas/FasL pathways Slow-acting Both converge on various caspase 3 activation leading to apoptosis

Question 36

CTL lytic action – enhances when

Answer 36

both mechanisms operate simultaneously

Question 37

CTL kills-dissociates-restarts process

Answer 37

1. nonspecific adhesion interaction 2.find its match 3. mediate killing 4. dissociate repeat for each cells desnt want to kill cells they dont need to kill Cytotoxic CD8 T cells can induce apoptosis infected target cells while sparing neighbouring uninfected cells

Question 38

... required in CD8+ T cell activation

Answer 38

CD3

Question 39

Type I IFN (a/b):

Answer 39

important anti-viral cytokines – can inhibit/slow viral replication

Question 40

Natural killer cells:

Answer 40

recognize & kill infected/tumor cells by their absence of MHC class I

Question 41

Virus-specific CTLs directly ...

Answer 41

directly kill infected cells

Question 42

CTLs secrete: ... cytokine!

Answer 42

IFNy – Type II IFN

Question 43

IFNy

Answer 43

o Increase MHC class I expression o infected cells o Activates macrophages & stimulates production of chemokines - recruit additional macrophages & CD8+ T cells to sites of infection

Question 44

Type I IFN

Answer 44

potent anticviral effects, effects of PRR activation

Question 45

Type II IFN

Answer 45

role in immune response against intracellular pathogens - secreted mainly by T cells