Lecture 31 - NK Cells 1 Flashcards
When were NK cells discovered?
What were the initial observation?
1975
Observations:
Cells that could kill tumour cells
Normal mice, non immunised Contain cells that kill the leukaemia cells Killing activity Spleen had more of the activity LN and BM a little Thymus none Indicated the location of these cells
Treatment with anti-Thy-1 serum, as well as removal of adherent and surface Ig positive cells from spleen enriches the activity (ie removing T cells, macrophages and B cells)
The remaining cells had the morphology of small lymphocytes
What are NK cells also called?
Large granular lymphocytes
Compare the following cells: • T cells • B cells • NK cells • NK T cells
T cells:
• CD3/TCR+
B cells:
• Surface Ig+
NK cells:
• CD3/TCR-
• Surface Ig-
• CD161 + (aka NK1.1+)
- CD56+ (also variable)
- CD16 (+/-)
NK T cells:
• CD3/TCR+
• Surface Ig-
• CD161+
What is CD161?
Surface antigen initially found to be on NK cells
aka NK1.1
“NK-type receptors”
Also found on NK T cells
What is the difference between NK T cells and NK cells?
Which arm of the immune response are they?
NK T cells:
• Express CD3/TCR
• Innate-like response
• Differentiate from DP thymocytes in the thymus
NK cells:
• Do not express CD3/TCR
• “Induced” innate response
• Differentiate from CLP in BM
Describe the major features of NK cells
• Main marker
• Function
- Lymphocytes
- CD3/TCR-
- Surface Ig-
- Express an array of receptors that control their activation
Main marker:
• NKp46
Function:
• Respond to a variety of viruses and tumours
• Do not undergo clonal expansion following infection (this was the dogma, but it’s currently under revision)
Which pathogens do NK cells respond to?
Viruses
Not bacteria
NB also respond to tumours
What is NK1.1?
CD161
What is the main marker of NK cells?
NKp46
What activates NK cells?
- Cell surface interactions
• CD16 (FcγRIII) → ADCC - Cytokines
• Type I interferon
• IL-12, IL-15, IL-18 - Natural cytotoxicity
• Missing self recognition of virally infected cells
Describe the effector function of NK cells
- Lysis of cells
• Perforin/Granzyme dependent
• Fas/FasL - Cytokine secretion
• IFN-γ
• TNF-alpha - Chemokine secretion
Thus, they are kind of like effector memory cells
What is CD16?
Where is it found?
FcγRIII
Found on the surface of NK cells (in humans)
CD3-like adaptor that contains ITAMs
When engaged it leads to ADCC
Describe Natural cytotoxicity
• “Missing self” hypothesis
• Direct recognition of virus infected cells or tumours
( • No Ab required, thus purely innate)
NK cell receptors:
• Activation receptors
• Inhibitory receptors; recognise MHC I
Signals:
• MHC I inhibition signal, uniquitous on healthy cells
• Activation signal; ubiquitous on all cells, or, in the case of NKG2D, can be up-regulated in conditions of cell stress
Process:
1. NK cells interrogate target cells through activation and inhibitory receptors
- Normally inhibitory receptor interaction with MHC I is dominant (?) and and activation signals (uniquitously present) are blocked
– viral infection –
- Down regulation of MHC I by virus (HSV, CMV, tumours, HIV)
– loss of MHC I –
- Predominance of activation signal
- Lysis of target cell
Describe ADCC with NK cells
CD16 (FcγRIII) associated with a CD3-like adaptor that contains ITAMs
- Infected cell bound with Ab
- FCγRIII (CD16) on NK cell binds Ab
- Cross linking of receptors
- Activation / clustering of ITAMs
- Intracellular transduction pathway
- Induction of cytotoxicity:
• Granzymes, Perforin, Serglycin - Target cell lysis
Discuss the inhibitory receptors
• Where they are expressed
• Superfamily
• What they recognise
3 types
- Ly49 receptors
• In rodents
• Expressed by rodent NK cells
• Family of receptors: C-type lectin superfamily (do not bind sugars though)
• Recognise classical rodent MHC I molecules (H-2K, H-2D)
2. Killer cell Immunoglobulin-like receptors (KIR) (CD158) • In primates • Primate NK cells • Members of Ig-superfamily • Recognise HLA-C & HLA-B (ie class I)
3. CD94/NKG2A • In rodents and primates (conserved through evolution) • Members of C-type lectin superfamily • Recognises non-classical MHC class I - HLA-E (in humans) - Qa-1(b) (in mice)
What is HLA-E?
Non-classical HLA in humans
Different from classical in that they are not polymorphic
There are only two alleles in the human population, differing by one amino acid
Both alleles are 50%
AA change doesn’t change the specificity of the receptor-ligand interaction
Describe, in general, signalling through inhibitory receptors on NK cells
ITIMs: motifs on the intracellular portion of receptors (ie Ly49 and CD158)
1. Ly49 Killer cell Immunoglobulin-like receptors (KIR) • Dimer • One ITIM on each subunit • YxxV
- CD158 / KIR
• Monomer
• Two ITIMs per tail
• YxxL - Engagement of ligands
- Tyrosine residues in ITIMs becomes phosphorylated
- Recruitment of phosphatase called SHIP
- Blockage of further activation (ie NK cell turned off, because the cell isn’t infected)
What is CD158?
NK inhibitory receptor only found in humans
aka Killer cell Immunoglobulin-like receptors (KIR)
Describe the different types of KIR receptors
Various ‘flavours’:
• Long/short cytoplasmic tails: L / S
• 2/3 domains: 3D / 2D
‘L’ and ‘S’ forms
• L forms have ITIMs and long cytoplasmic tails
• S: short cytoplasmic tail, no ITIMs
Domains
• 2D: two domains
• 3D: three domain
eg
• 2DL1
• 3DL2
Which KIR molecules have ITIMs?
‘L’ forms, ie those with long cytoplasmic tails
Describe signalling through KIR
2DL1, 2DL2 & 2DL3 most important
- Engagement of 2DL1 / 2DL2 / 2DL3 recognise subgroups of the HLA-C locus
- Phosphorylation of ITIMs
- Inhibition of NK cell
What do KIR receptors recognise?
Describe some features
Epitopes / regions on certain MHC class I molecules
Properties:
1. Mutually exclusive
• A given HLA allele can not be A3 as well as A11 etc.
• They are all completely independent
2. These epitopes are not found on all HLA alleles (eg mostly only found on HLA-C)
Properties shared by clusters of HLA alleles
2DL1, 2DL2 & 2DL3: • Subgroups of the HLA-C locus: • Group 1 and Group 2 alleles: ie - HLA-C1 - HLA-C2
3DL2:
• HLA-A3
• HLA-A11
3DL1:
• HLA-Bw4
Compare the ‘function’ or use of the various HLA groups
HLA-A & HLA-B
• Most important for priming T cell responses
HLA-C
• More important for controlling NK cell responses
NB HLA-A3/11 probably evolutionary remnants
Describe KIR epitopes within different ethnic groups
What is the implication of this?
Present in all ethnic groups, but in different proportions
Implication:
KIR epitopes are requisite for survival of population?
Compare Bw4 and Bw6 motifs
Motif found on HLA-B alleles
Located on alpha helix between residues 77-83
The residues in this location determines whether the allele is Bw4 or Bw6
Compare C1 and C2 epitopes
Defined by aa at residue 80:
Either Asn or Lys
Can either be one or the other
Thus, mutually exclusive
Describe the structure of KIR
Ig-like
Two Beta sheets in series
Interface between the two domains that generates the receptor binding site
(different from TCR)
Describe physically how KIR interacts with MHC:peptide
Interacts at one side of MHC
unlike with TCR, which interacts at the middle
Describe NK receptor expression within individuals
What is the significance of this?
Within an individual, NK receptor expression is variegated
(possible random?)
Some NK cells express each of: • CD158a (KIR-2DL1) • CD158b (KIR-2DL2/3) • CD158e (KIR-3DL1) • KIR-3DL2 • CD94/NKG2A
The same NK cell can express multiple receptors
Significance:
• Some viruses are sneaky and selectively down regulate MHC eg HIV down regulates HLA-A, HLA-B but not HLA-C or HLA-E
• Having NK cells with different receptor expression means that some NK cells will still be able to detect infection, even though not all MHC is down regulated
NB NK cells expression receptor for HLA-C will still see their ligand and think that the cell is healthy
Describe herpes virus HLA down-regulation
- When HSV infects a cell, is expresses a protein that interferes with TAP
- All types of HLA are not loaded with peptide
- They are retained in the ER and eventually destroyed
Describe clinical significance of Bw4 alleles
Associated with better outcomes
HIV protein Nef downregulates HLA-B, but doesn’t touch HLA-C
CD158e+ NK cells recognise HLA-Bw4
Thus, CD158e+ NK cells are really important in HIV infections and equate to a slowed progression to AIDS
Describe the clinical consequence of KIR-ligand matching in transplantation
Explain this phenomenon
Paper looking at BM transplant for the treatment of leukaemias
Looked through all the transplants and the genetics
Grouped people based on KIR-ligand-match or KIR-ligand-mismatch
Analysed success of transplant
No KIR-ligand incompatibility:
• 15% rejection
• 13% acute Graft vs Host disease
• 75% relapse in AML
KIR-ligand incompatibility:
• 0% rejection
• 0% acute Graft vs Host disease
• 0% relapse in AML
Explanation
• Distinct population of donor derived NK cells are preferentially activated when there is no ligand for them present
Example scenario:
• The donor cells express either CD158a, CD158b or CD158e
(Depending on the receptor, the NK cell recognises different ligands)
• Recipient cells express various ligands that inhibit all the various donor NK cells
• In this patient, there is no NK cell receptor mismatch –> rejection
• A different recipient has cells that express different ligands
• This person doesn’t have an MHC allele that inhibits eg CD158e+ NK cells or CD158a+ NK cells
• Some NK cells activated to mediate lysis and killing
–> no rejection
What is Graft vs Host disease?
Transplant performed
Graft immune system attacks the recipient of the organ
Describe what the following receptors recognise:
• CD158a
• CD158b
• CD158e
CD158a: Group 2 HLA-C
CD158b: Group 1 HLA-C
CD158e: HLA-Bw4
What is the point of BM transplants for leukaemia?
Graft that comes in clears tumours
Which FcR do NK cells have?
FcγRIII
