NK Cell Functions

Question 1

How are NK cells activated during viral infection?

Answer 1

By IFNa and IFNb released during viral infection.

Question 2

When is the NK cell response activated?

Answer 2

2 days after infection.

Question 3

Describe what happens when an NK cell encounters a normal, healthy cell.

Answer 3

There is more MHC class I expressed than activatory ligands on the normal cell, meaning that the NK cell inhibitory signal dominates and there is no induction of apoptosis.

Question 4

Explain the missing-self hypothesis in terms of NK cell activation.

Answer 4

Target cell does not express MHC class I, meaning there is no inhibitory signal, and the activating signals become dominant - activating the NK cell to trigger apoptosis of the target cell.

Question 5

How can there still be NK cell activation if MHC class I expression is maintained by the target cell?

Answer 5

There can be upregulation of the activatory ligands, allowing the activating signals to become dominant, and the NK cell can trigger apoptosis of the target cell.

Question 6

How does the CD16 Fc receptor activate NK cells?

Answer 6

Recognises antibodies bound to tumour antigens, or on the surface of infected cells -> promotes ADCC. Balance is shifted towards an activatory response as tumour cells overexpress the TSA.

Question 7

Give the cytokines produced by NK cells.

Answer 7

IL-10 and IFNy - act upon macrophages and T cells.

Question 8

How can NK cells dampen the immune response once an infection has been cleared?

Answer 8

Can kill immature DCs, hyperactivated macrophages, and activated CD4+ T cells.

Question 9

How do NK cells promote DC maturation?

Answer 9

Through the release of IFNy and TNFa.

Question 10

What is the outcome of DC maturation?

Answer 10

Enhanced antigen presentation to T cells.

Question 11

Give cytokines released by macrophages and DCs to stimulate NK proliferation.

Answer 11

Type I interferons, IL-15, IL-12 and IL-18.

Question 12

Give human ligands for NKG2D.

Answer 12

MICA, MICB and ULPB family members.

Question 13

Give murine ligands for NKG2D.

Answer 13

H60, MULT1 and Rae-1 family members.

Question 14

How is MCMV infection detected in mice?

Answer 14

Ly49h receptor on NK cells recognises an MCMV homolog of MHC class I, expressed by infected cells.

Question 15

How is immune evasion achieved in HCMV?

Answer 15

UL16 is a viral protein that blocks externalisation of ULPB in HCMV-infected cells, preventing activation of NK cells.

Question 16

What are KIRs?

Answer 16

Mainly inhibitory receptors that recognise MHC Class I and HLA-C.

Question 17

What is Ly49h equivalent to in humans?

Answer 17

KIRs.

Question 18

Discuss the evolution of KIRs and Ly49h.

Answer 18

Thought to have evolved separately despite having the same function, and there is no homology between them.

Question 19

What do activatory KIRs recognise?

Answer 19

HLA-Cw4 - overexpressed in tumour cells.

Question 20

What is the NKG2A/CD94 heterodimer?

Answer 20

An inhibitory receptor expressed by NK cells that recognises HLA-E.

Question 21

What is HLA-E?

Answer 21

HLA-E = Human Leukocyte Antigen E

- type of MHC molecule, often upregulated on tumour cells.

Question 22

How do NK cells kill tumour cells that express the TRAIL receptor?

Answer 22

Produces TRAIL which binds the receptor on the tumour cell and triggers the extrinsic pathway of apoptosis within the tumour cell.

Question 23

If a tumour cell has not downregulated MHC class I, what does its recognition by NK cells depend on?

Answer 23

The stress ligands expressed by the tumour cell.

Question 24

Where are the genes for the activatory receptors found in the human genome?

Answer 24

Chromosome 12 (NKC gene cluster)

Question 25

Where are most of the inhibitory receptor genes encoded in the human genome?

Answer 25

Chromosome 19

Question 26

Give the signalling domain in inhibitory receptors. What does this interact with?

Answer 26

ITIMs - interact with SHIP1 phosphatase to inhibit intracellular signalling.

Question 27

Give the signalling domain in activatory receptors.

Answer 27

ITAMs

Question 28

Give the proteins that interact with activatory KIRs and NKG2D.

Answer 28

activatory KIRs - interact with DAP12

NKG2D - interacts with DAP10

Question 29

What do DAP proteins interact with following activation of activatory receptors?

Answer 29

Zap70 tyr kinases

Question 30

What is NKG2D?

Answer 30

An activatory receptor expressed by all NK cells.

Question 31

Give the signalling proteins activated following NKG2D activation.

Answer 31

DAP10, DAP12 and PI3K.

Question 32

Describe the structure of NKG2D.

Answer 32

S=S linked homodimer.

Question 33

What are MICA, MICB and RAE-1 structurally similar to?

Answer 33

MHC

Question 34

What is NKG2D ligand expression induced by?

Answer 34

DNA damage, cellular stress and metabolic stress.

Question 35

Give evidence for the NK cell memory in response to MCMV infection.

Answer 35

• WT NK cells are transferred to immunodeficient (DAP12 -/-) mice, and these mice are infected with MCMV.
• Indicated an expansion of Ly49h+ NK cells (donor) at day 7 post-infection.
• after 50 days, only a few of these cells remained - are these ones memory-like?
• injection of memory-like NK cells into neonatal mice gives increased survival when challenged with MCMV.

Question 36

Give future questions that need to be answered about NK cell memory.

Answer 36

1. Is this a broad effect seen with other viruses / pathogens or specific to MCMV or viruses that have ligands that bind a NK cell surface receptor?
2. Is the expansion of NK memory cells at equivalent levels to that found with T cell and B cell memory on re-exposure to antigen?
3. Have NK memory cells a distinct phenotype?