C2 Cytotoxic T cells

Question 1

name some environmental cues in Tc activation

Answer 1

cytokines (IL-2, IL-12, IL-15) upreg activity

IL-18, IL-23, Il-27 upreg effector production

Question 2

what is required between CTL & target to induce killing/ how does it induce killing?

Answer 2

immunological synapse
kill target directly via granules/ perforin: apoptosis
or Indirectly via cytokines which are directly toxic: TNFa or induce toxic reactions: IFNy

Question 3

what does FasL bind to and what is the result

Answer 3

CD95 on target cell = caspase activity –> induces apoptosis

Question 4

what is role of perforin/ what is it essential for?

Answer 4

believe to form pore for granules to enter cells

perforin essential for granule mediated cytotoxicity - controlling tumors/ intracellular infections

Question 5

name the granzymes present in humans

Answer 5

4 - A,B,K & M
- B & A most abundant, B major constituent
(mice have 10)

Question 6

Describe granzyme A

Answer 6

1. Slower inducer of cell death than B
2. Damages DNA by single-strand nicks which = apoptosis: moves to nucleus & activates a DNAase (NM23-H1)
3. Need TREX1 (3’-5’ endonuclease) ((enzyme)) activation prevents DNA annealing and repairing
4. Activates oxidative stress in cell - increases reactive oxygen-species (ROS) - damaging

Question 7

Describe granzyme B

Answer 7

32Kda serine protease - caspase - enzyme that cleaves after aspartic acid residues
Could enter cells in perforin independent way - using mannose-6-phosphate receptor
KO studies using mice shown grB deficient CTL are less effective at killing and are required for caspase activity

Direct killing - can act on caspases - e.g. directly on caspase 3, 6, 7, 8, 9, 10 and via caspase 3 on caspase 2, 6, and 9 - stimulates apoptosis in target cell

Indirect killing - triggers mitochondrial permeabilization - release of inter-membrane spacer proteins e.g. cytochrome C = forms a complex (apoptosome - APAF-1 and caspase 9) - causes cell death

Question 8

Describe granzymes H, C, K

Answer 8

H - induces a caspase and BID-independent cell death via chromosomal condensation & nuclear fragmentation
C - induces mitochondrial depolarization and cytochrome c release
K - induces ROS and may kill like granzyme A

Question 9

describe direct cell death

Answer 9

formation of DISC: death inducing signaling complex - directly activates caspase FasL binds CD95
CD28 mediates protection against Fas activated cell death: inhibits intracellular signaling pathway
OR direct killing via TRAIL: TNF alpha related apoptosis-inducing ligand
When target cell dies by apoptosis it is removed by phagocytes or undergoes secondary necrosis and cell membrane lyses

Question 10

name a protective mechanism in cancer cells

Answer 10

express FasL can cause apoptosis of T cells which express Fas – protective mechanism by cancer cells

Question 11

true or false Tc can kill without MHC restriction

Answer 11

True -
Must be primed – cytokines, growth factors, mitogen or antigen
Close contact required to release granulysin – insert into microbial membrane – osmotic lysis
May need perforin
Mediates killing bacteria, protozoa, fungi

Question 12

Why are Tc not killed by their products?

Answer 12

cathepsin B – found in granules of Tc – can cleave perforin and protect the activated Tc
perforin kept in inactive state inside granules due to low pH
Serpin PI-9 - acts as a pseudo-substrate for granzyme B - forms irreversible complex which inhibits its function
CD28 enhances T cells survival in vitro - perhaps by increasing glucose consumption
- cd28 costim molecule

Question 13

describe Familial hemophagocytic lymphohistiocytosis

Answer 13

rare, fatal autosomal recessive immune disorder
uncontrolled activation of T cells and macrophages over production of inflammatory cytokines
curable with bone marrow transplant
(Genetic deficiency in perforin)