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n tur l killer

t cells

M. Benita Nancy Reni, 1.7.14

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NK T cell

NKT cells represent a distinct lineage of T cells that express an invariant T

Cell Receptor (TCR) and share a number of cell surface markers in common

with NK cells.

NKT cells are non-polymorphic CD1molecule-restricted T cells and are

activated by glycolipid antigens presented by CD1d.

They constitute only approximately 0.1% of all peripheral blood T cells.

The ability of these cells to produce Th1 and Th2-related cytokines has

implicated them in several fields, including transplantation, tumors,

autoimmunity, and allergy.

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can promote cell-mediated immunity to tumors and infectious organisms,

including bacteria and viruses, yet paradoxically they can also suppress the cell-

mediated immunity associated with autoimmune disease and allograft rejection.

Furthermore, in some diseases, such as atherosclerosis and allergy, NKT cell

activity can be deleterious to the host. Although the precise means by which these

cells carry out such contrasting functions is unclear,

NK T cell

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Classification

Type I cells(Classical NKTs)

invariant NKT (iNKT)

Type II cells

(Non-classical NKTs) NKT-like cells

CD1d dependent Yes Yes No

-GalCer reactive Yes No No

TCR chainV14-J18 (mice); V24-

J18(humans)

Diverse, but some V3.2-J

9, V8 (mice)Diverse

TCR chainV2, V7, and V8.2(mice);

V11 (humans)

Diverse, but

some V8.2(mice)Diverse

NK1.1 (CD161)

Positive (resting mature);

negative/low (immature or

post-activation)

Positive and negative Positive

Subsets CD4+, DN(mice); CD4+, CD8+, DN

(humans)

CD4+ and DN (mice) CD4+, CD8+, and DN

IL-4 production Yes Yes No

IFN-production Yes Yes Yes

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NK markers

NK1.1 (CD161) marker of activation (can also be expressed on activated

Tcon)

CD56 (NCAM)

neural cell adhesion molecule: important for cell adhesion

Expression of CD161 and V24J18 TCR can be used to identify

mouse and human NKT cells, respectively.

Expression of transcriptional repressor, Promyelocytic Leukemia

Zinc Finger (PLZF), in immune cells differs between mice and

humans.

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NK markers

In mice, PLZF is highly expressed in immature CD1d-resrictedinvariant NKT cells and a subset of gamma delta

(Vg1.1+Vd6.3+) T cells.

In humans, PLZF is expressed in NK cells, gamma delta T cells,

as well as CD4+ and CD8+ T cells. PLZF exists as a homodimer or in complex with PLZP, known to

be involved in the development of NKT cells, NK cell function,

cellular quiescence and growth suppression.

PLZP has also been shown to inhibit gene expression inducedby retinoic acid receptor.

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Development

NKT cells arise in the thymus from a common precursor pool of CD4+CD8+double-positive thymocytes that have undergone random TCR gene rearrangement and expression.Expression of a TCR that binds with appropriate avidity to MHC class II or I (MHCII or MHCI; plus self-peptide) on thymic epithelial cells leads to the positive selection ofconventional CD4+T cells (green) or CD8+T cells (blue), respectively. Thymocytes that express a TCR that binds to CD1d plus self-lipid or glycolipid antigen, expressed by otherdouble-positive thymocytes, enter the NKT cell lineage (red). Once selected, NKT cell precursors undergo a series of differentiation steps that ultimately results in the NKT cellpool. At least four distinct NKT cell development stages have been defined through differences in expression of CD24, CD44 and NK1.1; these are controlled by a series oftranscription factors (blue). NKT cells that emigrate from the thymus mostly do so at stage 2 and progress to stage 3 in the periphery. Some mature thymic NKT cells also migrateto the periphery but many remain as long-term thymus-resident cells. CD4NKT cells seem to branch from CD4+NKT cells at approximately stage 1 of development, althoughthey possibly do so earlier (dashed arrow). A separate pathway of NKT cell development gives rise to an IL-17-producing subset (NKT-17; orange) that seems to be regulated by

the transcription factor ROR-t. Much less is known about the developmental sequence of these cells (dashed arrow and question mark).

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Intracellular signalling pathways that regulate

NKT-cell development.

Natural killer T (NKT)-cell selection and maturation requires a range of signalling events that are not essential for conventional T-cell development, in addition to factors thatare common to both T-cell and NKT-cell development. The unique signalling requirements of NKT cells are not fully understood, but the three main intrinsic pathways thatlink most of the known mutants that affect NKT-cell development are depicted. These include the SLAM SAPFYN pathway, the T-cell receptor (TCR)-signalling cascade(particularly the classical nuclear factor- B(NF- B) pathway) and the interleukin-15 (IL-15) pathway. AP1, activating protein 1; c, common cytokine-receptor -chain; DOK,docking protein; I B ,inhibitor of NF- B ;IKK2, I Bkinase 2; JAK, Janus kinase; MAPK, mitogen-activated protein kinase; PKC ,protein kinase C ;RASGAP, RAS GTPase-

activating protein; SAP, SLAM-associated protein; SHIP, SRC-homology-2-domain-containing inositol-5-phosphatase; SLAM, signalling lymphocytic activation molecule;STAT, signal transducer and activator of transcription; ZAP70, -chain associated protein kinase of 70kDa.

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NK T cell; a jack of all trades

While NK T cells primary function is cytotoxicity (trait of NK and CTL lineages) they also have

helper characteristics as the secretion of IFN- or IL-4 induces T helper cells to differentiate intoeither TH1 or TH2 cells.

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iNKT

Unique subpopulation of T lymphocytes

true T cells: CD3 and TCR

semii invariant TCR diversity

also express some NK markers: CD161, CD56 Dependant for CD1d for antigen presentation.

Potential for both effector and regulatory functions -double-edged sword of the immune system

Very rare in the peripheral blood Implicated in autoimmunity, tumour immunity/control,

GvHD

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CD1d molecules

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Antigen Lipid antigens: lipids, glycolipids, lipopeptides

Bacterial: sphingomonas pg

Mycoplasma (TB & leprosy)

Isoglobotrihexosylceramide (iGb3):

> a glycolipid in the thymus that if present will

select for iNKT cells (iGb3 deficient mice aredeficient in iNKT)

Gal-Cer

galactsyleramide synthetic glycolipid derived from

a a marine sponge > strongest known agonist for iNKT

Glycolipid from tumour cell membranes

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Antigenic recognition by iNKT

iNKT cells recognise lipid antigens via non classicalCD1d molecules

CD1: related to MHC I but structural differences

Group I: CD1a, CD1b, Cd1c

Group II: CD1dGroup II: CD1d

> the lipid interacts with the antigen binding groove

of CD1a

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iNKT cells functions

Potential for both effector and regulatory

functions

double-edged sword of the immune system

form a bridge between innate and adaptive

immunity

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Effector function: cytotoxicity

Direct:

antigenic stimulation of iNKT cells leads to perforin,

FasL and TRAIL dependant direct cytotoxicity by the

iNKT cellsthemselves.

Indirect:

iNKT cells produce INF which stimulates cytotoxicCD8 and NK cells.

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Regulatory function

Produce large amounts of regulatory cytokines: IL4 Th2 response (humoral immunity)

IFN-, and TNF Th1 (cell mediated immunity)

Can skew towards Th1 or Th2 or both!!!!

Regulate the function of DC, macrophages, B cells, T

cells, NK cells

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NKT and autoimmunity

Scleroderma:

restricted TCR diversity with absence of TCR V 24

SLE:

skewing towards IL4 secreting cells with reduction in NKT

numbers and production of B cells that produceantiDSDNA

Type I diabetes:

NOD (non obese diabetic) mice are deficient in NKT

onset of diabetes can be prevented by adoptive transfer of

thymic iNKT cells

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NKT and cancer

Tumour cell clearance and prevent metastasis

increased NK cell cytotoxicity (IFN- mediated) - mousemodels of colon adenocarcinoma melanoma lung carcinoma

Tumour surveillance NKT deficient mice (lack CD1d or TCRJ 18) exposed to

carcinogens developed tumours faster than immunocompetentmice

NKT cells contribute to tumor immuno-surveillance viaendogenous IL-12 pathway, early IFN

NKT cells promote effective responses in anti-tumor

vaccinesystems. CD1d down-regulated on tumor cells from human

patients

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Activation by -GalCer leads to potent tumor

rejection, (pulsed DCs even better)

Tumor rejection due to administration of exogenous

IL-12 is CD1d dependent

NKT cells contribute to tumor immuno-surveillance

via endogenous IL-12 pathway, early IFN

NKT cells promote effective responses in anti-tumor

vaccine systems

CD1d down-regulated on tumor cells from human

patients

NKT and cancer

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iNKT and GvHD

Mouse models: that low iNKT associated with

GvHD

Adoptive transfer can abrogate GvHD

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Thank you..