TLR7/8-mediated activation of human NK cells results in accessory cell-dependent IFN-gamma production.
NK cells express receptors that allow them to recognize pathogens and activate effector functions such as cytotoxicity and cytokine production. Among these receptors are the recently identified TLRs that recognize conserved pathogen structures and initiate innate immune responses. We demonstrate that human NK cells express TLR3, TLR7, and TLR8 and that these receptors are functional. TLR3 is expressed at the cell surface where it functions as a receptor for polyinosinic acid:cytidylic acid (poly(I:C)) in a lysosomal-independent manner. TLR7/8 signaling is sensitive to chloroquine inhibition, indicating a requirement for lysosomal signaling as for other cell types. Both R848, an agonist of human TLR7 and TLR8, and poly(I:C) activate NK cell cytotoxicity against Daudi target cells. However, IFN-gamma production is differentially regulated by these TLR agonists. In contrast to poly(I:C), R848 stimulates significant IFN-gamma production by NK cells. This is accessory cell dependent and is inhibited by addition of a neutralizing anti-IL-12 Ab. Moreover, stimulation of purified monocyte populations with R848 results in IL-12 production, and reconstitution of purified NK cells with monocytes results in increased IFN-gamma production in response to R848. In addition, we demonstrate that while resting NK cells do not transduce signals directly in response to R848, they can be primed to do so by prior exposure to either IL-2 or IFN-alpha. Therefore, although NK cells can be directly activated by TLRs, accessory cells play an important and sometimes essential role in the activation of effector functions such as IFN-gamma production and cytotoxicity.
Hart
Orla M
OM
Department of Biochemistry, Trinity College, Dublin, Ireland.
Athie-Morales
Veronica
V
O'Connor
Geraldine M
GM
Gardiner
Clair M
CM
D000938:Antigen-Presenting Cells / Q000276:immunology*; D002460:Cell Line; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007371:Interferon-gamma / Q000096:biosynthesis*; D018664:Interleukin-12 / Q000502:physiology; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology*; D008247:Lysosomes / Q000378:metabolism / Q000502:physiology; D008562:Membrane Glycoproteins / Q000819:agonists / Q000096:biosynthesis / Q000502:physiology*; D055627:Natural Cytotoxicity Triggering Receptor 1; D055629:Natural Cytotoxicity Triggering Receptor 2; D055628:Natural Cytotoxicity Triggering Receptor 3; D011070:Poly I-C / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000819:agonists / Q000096:biosynthesis / Q000502:physiology*; D011971:Receptors, Immunologic / Q000096:biosynthesis; D055607:Receptors, Natural Killer Cell; D015398:Signal Transduction / Q000276:immunology; D051196:Toll-Like Receptor 3; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; D051193:Toll-Like Receptors
D007093:Imidazoles; D008562:Membrane Glycoproteins; C112260:NCR1 protein, human; C112837:NCR2 protein, human; C431710:NCR3 protein, human; D055627:Natural Cytotoxicity Triggering Receptor 1; D055629:Natural Cytotoxicity Triggering Receptor 2; D055628:Natural Cytotoxicity Triggering Receptor 3; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D055607:Receptors, Natural Killer Cell; C495344:TLR3 protein, human; C495348:TLR7 protein, human; C495349:TLR8 protein, human; D051196:Toll-Like Receptor 3; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; D051193:Toll-Like Receptors; D018664:Interleukin-12; D007371:Interferon-gamma; D011070:Poly I-C; C402365:resiquimod