May 11, 2015
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