Natural killer cells - Block C lecture one Flashcards
where do NK cells develop ?
They do not develop in the thymus - development starts in Bone marrow and then continues in secondary lymphoid organs e.g. Lymph nodes and tonsils
What cytokines and markers are required for NK development ?
IL-15 from Antigen Presenting Cells such as dendritic cells and CD56 marker are required for development
what are the ligands for NK cells ?
MHC class I/MHC class I-like molecules restricted
is recognition reliant on specific antigen receptor and do they require RAG1 and RAG 2 ?
Recognition is not reliant on specific antigen receptor. They do not have rearrangement of their receptor genes; this is proved because if RAG1 and RAG2 are knocked out in mice there is still NK cells produced
CD3 expressed on NK cells?
no
CD56 ?
yes , CD56+ is expressed isoform neural adhesion factor)
NKp46+
natural cytotoxicity factor, not specific to NK cells) - but no simple marker
are the markers on the NK cell specific to it ?
The markers on the NK cell are not specific to just it , they are also found on other immune cells.
role of IL-21 in development of NK cells ?
IL-21 cytokine induces maturation of human CD34+ cells (stem cells) into NK cells and they become different populations.
CD56 dimCD16+ cell subset ?
CD56dimCD16+ cell subset that represents the majority of NK cells - 90% of blood is NK cells
where are CD56 bright cells found ?
in the secondary lymphoid tissue/tissue cells
if the NK has a high level of granzymes what would this indicate ?
If the granzymes are high then this could be an effector cell.
what are the INK ?
the receptors on the surface of the NK cells
what are the 2 main roles of NK cell ?
secrete cytokines/chemokines and influence immune response main cytokines produced are tumour necrosis factor-α (TNF-α) and interferon γ (IFN-γ)
Kill infected/transformed cells activity very like Tc BUT:
•cytoplasm has granules in it – constitutively expressed whereas Tc cells ( cytotoxic T cells) need to be stimulated before they produce granules. The NK cells are always ready for attack.
how do the NK cells detect the infected cells ?
Interact with infected (virus)/malignant (cancer) cells which have reduced expression of MHC class I molecules which markers it for killing. However, human NK cells can also kill dendritic cells (DC) by apoptosis which express normal amounts of HLA molecules.
can NK cells bind to a pathogen and kill it directly ?
Can only kill your own cells NOT a pathogen by direct contact. They cannot bind to the pathogen like a bacteria cell , they bind to your own cells that are infected with the pathogen.
how do NK cells become activated ?
‘opposing signal’ is the method of activation
positive and negative regulators and the balance of stimulation of activation receptors and inhibitory receptors determines whether they are activated
So you have some ligands/receptors/ things on the surface that can attach to something that will activate it, and some things where a ligand engages with it inhibits it and switches off.
There’s inhibitory and activating receptors , which are signalling inside the cell and this balances decides whether a cell is activated , and can induce apoptosis in infected cells and produce cytokines and chemokines.
think of a tug of war contest
if there are 2 inhibitory interactions and only one activating what occurs ?
there is no activation.
if the cell interaction has no MHC and a primary activating interaction what occurs ?
loss of MHC molecules in the tumour cell which promotes cell killing and a primary activating interaction so that killing occurs.
what does the activation signalling receptors require ?
activation requires receptors such as Natural cytotoxicity receptors, killer cell immunoglobulin-like receptors (KIR).
inhibitory signalling ?
inhibitory immunoglobulin killer receptors (KIR) important as they recognise class Ia (HLA-A, B, C) ligands and or non-classical class Ib ligands (HLA-E)
cytokines involved in activation ?
cytokines involved are IL-2, IL-12, IL- 15, IL-18, IL-21, IFN a/b - can induce cell proliferation, or NK induced cytotoxicity and/or production of IFN-g.
when are NK cells recruited as part of the response ?
NK cells recruited to tissues during an inflammatory response. The NK cells move up the concentration gradient to the infection site where they are required
what are the 2 types of receptor: inhibitory and activating binding to ?
The 2 types of receptors ( activating and inhibitory) are binding to the ligands on the surface of the target cell. it is the overall balance of the receptors between activating and inhibition which lead to the response. If activating, then in the diagram the granzymes are released which target the cell and apoptosis occurs.
what is immunological synapse ?
Close contact required between target cell and immune cell– immunological synapse
what allows the immunological synapse to form ?
adhesion molecules e.g. alpha4beta2 integrin and leukocyte function-associated antigen-1 (LFA-1) and beta1 integrins - form immunological synapse to allow contact.
LFA-1
LFA-1 transduces signals which result in an NK-cell target conjugate and can be sufficient to trigger NK cytotoxicity
nectin / nectin like molecules ?
belong to immunoglobulin superfamily so 2 polypeptide chains
Cellular adhesion molecules involved in calcium independent cellular adhesion
expressed on epithelial cells and help to form junctions between cells
highly expressed on tumour cells and become accessible when the structure of epithelium is disrupted.
If signal strong between the ligand and NK cell then it can result in cell cytotoxicity by NK cell
Show importance by using people with specific deficiencies to nectins shows NK cells not as active.
what does LFA-1 and ICAM-1 result in ?
interaction of LFA-1 with ICAM-1 results in granule polarisation (lined up at immunological synapse)
role of CD16 ?
CD16 is Fc receptor of IgG results in degranulation which stimulates antibody dependent cell mediated cytotoxicity ( ADCC). This is called opsonisation.
granule release ?
Release of granules may rely on 2 signals – but the cell needs an overall activation signal.
Activation like CTL cells - involves perforin and caspase 3 activation in target cell which induces apoptosis of cell target, this results in no inflammation.
what will short term exposure to IL-12 result in ?
Short-term NK exposure to IL-12 then the NK cells release lots of IFN gamma and TNF alpha and high cytotoxic activity (classed as effector NK cells) in LN - promote Th1 response
EFFECTOR NK CELL
exposure to IL-18 from dendritic cells result in ?
Exposure to IL-18 (from DC cells) promotes development of CD56+/CD83+/CCR7+/CD25+ cells (helper NK cells) could be migratory NK cells which favour Th1 response
HELPER NK CELL
3 main types of NK cell receptors ?
killer immunoglobulin like receptor (KIR)
Heterodimeric c-lectin receptors ( CD94 and NG2)
Natural c lectin receptors
KIR
Exist as pairs inhibitory/activating receptors
- Recognise HLA A, B and C molecules in humans
- Not a KIR for every HLA type – recognise a group of molecules which suggests homology in A.A sequence to allow binding.
- what is recognised by each receptor not yet defined in some cases
heterodimeric C lectin receptor
Made from 2 proteins
Made from CD94 covalently linked to a product of the NG2 gene
CD94/NG2a inhibitory
Recognise non-classical MHC-class-1 and class I molecules
natural cytotoxicity receptors ?
ligand may not defined on target cell
- used in killing of tumour cells so not found on our own healthy cells
- human NK cells kill Dendritic Cells by activation of the calcium-calmodulin kinase triggered by engagement of LFA I (adhesion molecule) - results in degranulation
- block with specific inhibitor of calcium-calmodulin kinase II
- only activated NK cells can kill DC – e.g. during viral infections not our own cells
- Also can be activated by engagement of the phosphatidylinositol 3-kinase and causes ligation of NK cytotoxicity receptors NKp30 and NKp46
DC editing ?
DC editing - NK cell involved in controlling quality and quantity of DC - eliminate DCs at immature stage, and therefore bona fide tolerogenic DCs - NKp30 receptor involved
human sudy , patients with genetic mutation in beta 2 integrin ( CD18)
have NK cells which are less cytotoxic. No CD18 then no antibody induced cytotoxicity
hyper IgM syndrome
hyper-IgM syndrome due to a mutation in the CD40 ligand gene resulted in natural killer (NK) cell deficiency. Decreased levels of immunoglobin G in the blood and normal or elevated levels of IgM. Patients have no CD56+ or CD16+ cells and no NK activity.
Hermansky Pudlk syndrome 2
an autosomal recessive disease characterized by partial albinism - have NK cells with low perforin levels and NK cells have low cytotoxic activity.
