NK cells in Viral immunity

By Manmohan Mishra

Msc Virology9/10/2013

HISTORY

OVERVIEW OF NK CELL

NATURAL KILLER CELLIf there is no MHC-1 on intestinal Cells, what will happen to then ?

ACTIVATION - IL-12, IFN-ᵞ

MATURATION - DNN THYMUS, INTRACELLULAR PATHOGENMATURE IN BONE MARROW

ANTIGEN - DO NOT NEED EXPOSURE TO ANTIGEN

SP. ANTIBODY - NO MEMORY ABILITY

MARKERS- NO CD4, CD8, CD3 YES- CD16,56

Intracellular ExtracellularPathogen Pathogen

TH0 IL-12 IL-4

IFN-ᵞ × TH1 TH2 × IL-2 IL-4,5,6,10,13

IFN-ᵞ TNF TGF-ß

IL-12 ,IFN- ᵞ

NK

CELL

Development of NK cell

INTRODUCTION

• NK cells (group Innate lymphoid cells) – large(15µm), granular, bone marrow-derived lymphocytes that display cytotoxic activity against a wide range of tumor cells in the absence of any previous immunization with the tumor.

• Named “NK cells” - initial notion - do not require activation to kill cells that are missing “self” markers of  MHC class 1

• NK cells donot express TCR or B cell surface immunoglobulins.

NK cell

NK CELL CD SURFACE MARKERS AND FUNCTIONS

CD NUMBER FUNCTION

CD2 ADHESION MOLECULE & BINDS CD58 ACTIVATES NK CELLS

CD11b PHAGOCYTOSIS OF iC3b COATED PARTICLES

CD11c SIMIAR FUNCTION TO CD11b

CD16 IMMUNE COMPLEX INDUCED CELLULAR ACTIVATION, ADCC

CD56 HOMOTYPIC ADHESION

• NK cells - 5%–10% of total lymphocytes in human Peripheral Blood

• NK cells differ from NK1-T phenotypically, by origin and by respective effector functions

• Sometimes NK1-T cell activity promotes NK cell activity by secreting IFNγ

NK1-TCELL

CHARACTERISTIC OF BOTH NK & T CELL

LIKE TCELLS THEY HAVE TCR INTERACT WITH MHC LIKE MOLECULE CD1 RATHER THAN MHC 1 OR 2

LIKE NK THEY HAVE CD16 (VARIABLE LEVEL) & OTHER RECEPTORS & THEY KILL INFECTED CELLS

A popln of NK1-T cells - rapidly secrete large amounts - cytokines - support antibody prodn by B cells, inflammation and the development and expansion of CTLs.

TLR signaling- result in the recruitment and activation of macrophages, NK cells, and dendritic cells, key agents in the presentation of antigen to T cells

Role of NK cell in Innate & Adaptive immunity

• Nk cells - effectors of innate immunity

• NK cell - role in adaptive immune response

• The ability for NK cells in both the innate and adaptive immune response - important in research utilizing NK cell activity and potential cancer therapies

ROLE IN INNATE IMMUNITY• NK cell–dendritic cell crosstalk

-NK cells can kill iDCs, NK cells and DCs reciprocally activate one another during an immune response

NK cell function in adaptive response

Ability to generate memory cells following a primary infection

Consequent rapid immune activation

Response to succeeding infections by the same antigen

(Fundamental to the role T and B cells play in the adaptive immune response)

Despite prior belief - NK cells play no role in the adaptive immune responses, been found to undergo expansion, contraction, memory maintenance and recall

NK cell receptors

• NK cell receptors - differentiated based on function.

• 2 different categories of receptors

TWO RECEPTOR MODEL

Inhibitory receptors –delivers inhibition signals to NK cells

Activation receptors- delivers activation signals

ACTIVATION RECEPTORS

Ig SFCD16 (FcγRIII),CD28,KIR2S, KIR3S,NCR (NKp30, 44, 46),ILT-1 (Ig-liketranscript 1)

Cyto RCD25 (IL-2Rα)

CD122 (IL-2Rβ)

IFN-α/βR

TNFRSFCD27

C-lectinCD69CD94/NKG2C, ECD161NKG2DLy49D, H, P

CD16

SPECIES- H, M

MOTIF/ADAPTOR-ITAM/FcᵞR

LIGAND- IMMUNE COMLEX-ADCC

CD28- SPECIES- H,M

MOTIF/ADAPTOR-YXXM/P13K

LIGAND- CD 80,86

CD226SPECIES- H

LIGAND-CD112,CD155

KIR2S/KIR3SSPECIES- HMOTIF/ADAPTOR- ITAM/DAP12LIGAND – HLA 1

CD25(IL-2Rß)- HLIGAND- IL-2

CD122(IL-2Rß)H,MJAK-STATIL-2,15

IFN-αßrH,MJAK –STATLIGAND- TYPE1 IFN

CD27H,MTRAFCD70

CD69H,MCD94/NKG2C-H,MITAM/DAP12HLA,E

LY49MITAM/DAP12H-2

NCR(NKP30,44,46)H,M(NKp46)ITAM/DAP12VIRAL HAEMAGGLUTININS

-

INHIBITORY RECEPTORS

IgSF

CD85HITIMHLA-A,B,G

KIR2DL/3DLHITIMHLA-1

C-LECTIN

CD94/NKG2AH,MITIMHLA-E

CD161MITIMNKR-P1D

LY49MITIMH-2

KLRG1MITIM

SLAM

CD244-

H,M

TXYXXV-1

CD-48

CYTO-R

TGF-ßrH,MSmad2TGF-ß FAMILY

IL-10RJAK-STATIL-10

Missing 'self' hypothesis

• Opposing-signals model - balance betn activating signals and inhibitory signals - enable NK cells to distinguish healthy cells from infected or cancerous ones.

IRs- in cytoplasmic domain structural motif ITIMs

As IR bind MHC-1 ITIMs phosphorylated on tyrosine residues – phosphorylated ITIMs bind and promote the action of cytoplasmic protein tyrosine phosphatases.

These phosphatases remove the phosphate group of from tyrosine residues of various signaling molecules thus block the activation of NK Cells Through Activation Receptors

NKG2D MECHANISM

CMV VS NKG2D

CMV VS NK CELL

Acquisition of NK cell function

FunctionCYTOTOXIC MECHANISMS (THE ‘WEAPONS’)

• NK cells are cytotoxic

small granules in their cytoplasm contain proteins - Perforin and proteases known as Granzymes

Upon release - close proximity to a cell , perforin forms pores in the cell membrane - target cell - an aqueous channel through which the granzymes , associated molecules enter - inducing either apoptosis or osmotic cell lysis

Lysing a virus-infected cell- potentially only release the virions,

whereas

Apoptosis leads to destruction of the virus inside.

α-defensins, an antimicrobial is also secreted by NK cells, directly kills bacteria by disrupting their cell walls analogous to neutrophils

PERFORIN

PORE FORMING PROTEIN

ENCODED BY PRF1 GENE

CYTOLYTIC PROTEIN FOUND IN GRANULES CTLs & NK CELLS

UPON DEGRANULATIONINSERTS ITSELF INTO TARGET CELL PLASMA MEMBRANE, FORMS PORE OR ENDOSOME ALLOWINGRANZYMES TO ENTER TARGET CELL CYTOPLASM

THE LYTIC MEMBRANE-INSERTING PART OF PERFORIN IS MACPF  DOMAIN

Granulysin- (humans) function similarly to perforin

GRANULE EXOCYTOSIS

GRANZYME B

Protease located in cytoplasmic granules of killer cells

Cleaves after aspartate residues that have the sequence: Ile/Val-Gly/Met/Glu-X-Asp-X-Gly

Caspase 3 and 8 are direct substrates for granzyme B

Caspases are cysteine proteinases involved in apoptosis

Other granzymes in granules (granzyme A, K, M)

GRANZYME -A APOPTOSIS PATHWAY

NK CELL

Antibody-dependent cell mediated cytotoxicity( ADCC)

Cytokine-induced NK and CTL activation

• Cytokines play a crucial role in NK cell activation

• Cytokines- stress  molecules released by cells upon viral infection, they serve to signal to the NK cell the presence of viral pathogens.

• Cytokines involved in NK activation include IL-12, IL-15, IL-18, IL-2, and CCL5.

• NK cells - activated in response to interferons or macrophage-derived cytokines.

Nk cells respond to IL-12 produced by macrophages & secrete IFN- γ, which activates the macrophages to kill phagocytosed microbes

NK CELL CYTOKINES

Interferon gamma (IFN-):

- activation, growth and differentiation of T, B, NK cells and macrophages

-promotes Th1 differentiation

-enhances MHC expression on APC

-some direct anti-viral activity

Tumour necrosis factor alpha (TNF-):

-paracrine and endocrine mediator of inflammation

-regulates growth and differentation of a wide variety of cells

-selectively cytotoxic for many transformed cells

Granulocyte/macrophage colony stimulating factor (GM-CSF):

-survival and growth factor of HSCs

-differentiation and activating factor for granulocytic and monocytic cells

-growth factor for endothelial cells, erythroid cells, megakaryocytes and T cells

• They serve to contain viral infections while the adaptive immune response is generating antigen-specific cytotoxic T cells that can clear the infection.

• NK cells work to control viral infections by secreting IFN γ and TNF α.

• IFN γ activates macrophages for phagocytosis and lysis, and TNFα acts to promote direct NK tumor cell killing.

• Patients deficient in NK cells prove to be highly susceptible to early phases of herpes virus infection.

ANTIVIRAL FUNCTIONS

ULBPNKG2D