Lecture 8: Natural Killer Cells

Question 1

Describe NK cells.

Answer 1

Natural Killer Cells are:

• Lymphocytes
  
  • part of the ILC (Innate Lymphoid Cells)
• Development requires expression of
  
  • Id2, Nfil3, and Eomesodermin
  • Presence of IL-15

Question 2

Development of NK cells requires the expression of ____________.

Answer 2

Id2, Nfil3, and Eomesodermin (in the presence of IL-15)

Question 3

Recall info regarding receptors of NK cells.

Answer 3

NK cells lack any Ag-specific receptors. Very few receptors are uniquely expressed by NK cells. Most commonly used combination to detect NK cells is CD56+ CD3-.

Question 4

What do NK cells do?

Answer 4

• lyse target cells
  
  • by release of cytotoxic granules (perforin/granzyme)
  • by inducing cell death (TRAIL and interaction with DR4/5 - activation of Caspase 8)
• Secrete cytokines
  
  • IFN-gamma. TNF alpha
• Secrete chemokine
  
  • XCL1 (recruits dendritic cells)

Question 5

Describe the mechanism of lysis by NK cell.

Answer 5

Nk cells express the TNF family ligand TRAIL on their cell surface, which can bind and activate DR4 and DR5 expressed by some cell targets. Engagement of DR4/5 leads to a signal via the FADD to activate caspase 8, which induces apoptosis in the target cells.

Question 6

What turns on natural killer cell?

Answer 6

Question 7

Describe the antibody-dependent cellular cytotoxicity of NK cells.

Answer 7

Question 8

Describe the missing cell hypothesis.

Answer 8

Virus-infected or transformed cell has a downregulation of MHC class I molecules (to avoid CD8+ T cells), However, with less MHC class I, less inhibitory signals are received by NK cells through inhibitory receptors (such as KIR), hence lysing the cell.

Tumour cells frequently have defective class I expression.

Question 9

NK cell activation is controlled by multiple _____________________ encoded in ____ distinct genetic clusters.

Answer 9

NK cell activation is controlled by multiple inhibitory receptors encoded in two distinct genetic clusters.

Question 10

Describe the mechanism of the activation of inhibitory receptors in NK cells.

Answer 10

Inhibitory receptors signal via Immunoreceptor Tyrosine-based Inhibitory Motifs (ITIM). The tyrosine in ITIM is phosphorylated and it recruits and activates the phosphatases SHP-1/2. They could then dephosphorylate Tyr residues on other signalling molecules.

Question 11

Mention and describe inhibitory receptors in NK cells.

Answer 11

1. Ly49 receptors
   
   • expressed by rodent NK cells
     
     • only 1 gene in humans (functional?)
   • family of receptors
   • members of the C-type lectin superfamily
   • recognize different MHC class I molecules
2. KIR (CD158)
   
   • expressed by primate NK cells
   • family of receptors
   • members of the Ig-superfamily
   • recognize groups of HLA-A, -B, and -C allotype
   • genetically variable
3. CD94/NKG2A
   
   • expressed by both rodent and primate NK cells
   • members of the C-type lectin superfamily
   • recognize non-classical MHC class I molecules
     
     • HLA-E (humans)
     • Qa-1b (mice)

Question 12

Recall the variability fo KIR

Answer 12

Question 13

Recall about the nature of binding between KIR and MHC-I.

Answer 13

KIR binds over the alpha-1 and alpha-2 domain of the HLA-I. The domains are sensitive to polymorphism - hence a KIR only binds to a subset of HLA. KIR are also sensitive to the sequence of the HLA-associated peptide

Question 14

Recall on how KIR haplotypes are associated with disease/health outcomes.

Answer 14

• A haplotypes - pre-eclampsia
• B-haplotypes
  
  • improved CMV control
  • reduced relapse in leukemia patients the following transplantation

Question 15

What is the function of non-classical MHC class I molecules?

Answer 15

HLA-E/Qa-1b have peptide-binding clefts specialised for presenting conserved peptides present in the signal sequence of other MHC class I proteins.

Question 16

Expression of any particular HLA class I molecules will inhibit ___________________.

Answer 16

activation of only a subset of NK cells

Question 17

Recall the mechanism of “educational licensing” of NK cells.

Answer 17

NK cells with no interactions between inhibitory receptors and self-peptide MHC class I is less lytic compared to those with more interactions. Those cells could be said to be “unlicensed”.

Question 18

Recall the mechanism of natural cytotoxicity of NK cell.

Answer 18

Activating receptors typically signal through tyrosine phosphorylation of dimeric adaptor molecules.

Question 19

Recall information regarding NKG2D ligand expression.

Answer 19

• Tightly regulated expression: indicates cellular stress
  
  • Non-constitutive
    
    • low or absent in most adult tissue
  • Inducible
    
    • Heat shock
    • Viral infection (CMV)
    • Bacterial infection
  • Frequently expressed on tumours/transformed cells
• Initiated by protein kinases ATM or ATR
  
  • induced as a result of DNA damage

Question 20

Describe NKG2D and its ligands.

Answer 20

It is an activating receptor, expressed by all NK and certain T cell subsets. It is a potent activator of NK cells through the costimulation of T cells (γδ and CD8 αβ​).

It has multiple ligands:

• Human:
  
  • MIC-A/B
  • ULBP

These ligands are MHC class I-like molecules, which do not bind to peptides and do not associate with β2 microglobulin

Question 21

Recall regarding the balance of stimulatory and inhibitory signals on the NK cell activation.

Answer 21