NK cells

Question 1

where are NK cells found

Answer 1

the bloodstream

Question 2

what sort of response do NK cells inflict

Answer 2

anti viral/anti-tumourgenic cytotoxic response

Question 3

are NK cells antigen specific

Answer 3

no, they recognise generic features of abnormal cells such as loss of MHCI

Question 4

give 4 examples of NK activating receptors

Answer 4

NKG2D, Cd16, 2B4 and NKp46

Question 5

on which cells are nk activating receptors upregulated

Answer 5

virally infected or cancerous cells

Question 6

what is the result of ligand binding to NK activating receptors

Answer 6

cell killing by granule release

Question 7

what are some of the ligands for NKG2D activating receptor

Answer 7

UL16 binding proteins, ULBP1-4 and MHCI related molecules MCA and MICB

Question 8

under what circumstances is NKG2D upregulated

Answer 8

cellular stress eg oxidative stress, heat shock and genotoxic stress

Question 9

which virus target UL16 ligand of NKG2D receptor

Answer 9

human cytomegalovirus and karposi’s sarcoma associated herpes virus K5 protein

Question 10

what type of ligand does the CD16 NK activating receptor bind

Answer 10

fc region of IgG antibodies- acts as an intermediate between adaptive and innate

Question 11

what type of response does IgG binding to CD16 activating receptor elicit

Answer 11

antibody-dependent cellular cytotoxicity

Question 12

which cells do NKp46 and 2B4 recognise

Answer 12

cells infected with common viral pathogens

Question 13

what is the ligand for NKp46 activating receptor

Answer 13

influenza virus aglycoprotein haemaglutnin

Question 14

which ligand does activating receptor 2B4 bind

Answer 14

CD48 expressed by B-lymphocytes. expression of this ligand in B cells is activated by EBV infection

Question 15

which ligand do many NK inhibitory receptors bind

Answer 15

MHCI

Question 16

describe the missing/altered self hypothesis

Answer 16

MHCI is down regulated by viruses and cancer cells. when it is not expressed on the cell surface the inhibitory receptor cannot bind thus leading to no inhibition signal and thus activation

Question 17

how do CD94/NKG2A act as inhibitory receptors

Answer 17

normally bind HLA-E but loss of MHCI molecules results in the loss of signal peptides which results in the loss of HLA-E expression and so inhibitory signals are stopped

Question 18

describe the signalling cascade of CD16 and NKp46

Answer 18

ITAM domains in the cytoplasmic region of the receptors propagate signals via syk kinases

Question 19

describe the signalling cascade of inhibitory receptors in the presence of ligand

Answer 19

binding iduces phosphorylation of the tyrosine in the ITIM domain and recruitment of phosphates which dephosphorylate intracellular targets, inhibiting NK activation

Question 20

what do granules released by NK cells contain

Answer 20

perforin and granzymes

Question 21

how do granules only kill abnormal cells

Answer 21

secretion is polarised towards the contact point in the lytic immunological synapse

Question 22

describe the 3 stages of granule exocytosis

Answer 22

1. immunological snaps is formed. around it you het receptor signalling and cytoskeletal actin thinning so granules can dock and fuse with the membrane. adhesion molecules form a ring around the synapse and signalling molecules cluster at the centre of the synapses.
2. the microtubule organising centre (MTOC) shifts towards the synapse so granules re polarised towards the synapse
3. granules fuse with the PM and release cytotoxic molecules

Question 23

how is granule release disrupted in griselli’s syndrome

Answer 23

a mutation in Rab27a prevents granule docking

Question 24

how is granule release disrupted in FHL4

Answer 24

mutations in syntaxin 11 (a snare protein) prevents fusion of granules with the membrane

Question 25

how is granule release disrupted in FHL5

Answer 25

mutations in Munc18-2 which binds syntax 11 to regulate snare mediated membrane fusion

Question 26

how does perforin release result in abnormal cell death

Answer 26

it facilitates granzyme entry int the cytoplasm by somehow permeabilising the membrane to endocytosis so that granzyme may be taken up by endocytosis

Question 27

how does granzyme release result in abnormal cell death

Answer 27

Granzyme Band other granzymes cleave substrates within the target cell. Granzyme B targets caspase 3 which causes apoptosis. it also targets BID. cleavage of BID results in release of proapoptotic factors incl. CytC which activates caspase 9 which in turn activates caspase 3. Caspase 3 acts by activating ICAD to form CAD which results in DNA fragmentation of viral DNA

Question 28

which cytokines are able to activate NK cells

Answer 28

IFNa/b secreted by virally infected cells activate NK by increasing amplification and cytotoxic capacity.
IL-12 produced by infected dendritic cells and macrophages. this promotes NK cells to secrete IFNg which increases MHCI presentation by cells ad activates macrophages