Distinct indirect pathways govern human NK-cell activation by TLR-7 and TLR-8 agonists

Int Immunol. 2006 Jul;18(7):1115-26. doi: 10.1093/intimm/dxl046. Epub 2006 May 25.


NK cells limit the emergence of cancers and viral infections by surveillance of 'missing-self' and 'induced-self' ligands, and by direct recognition of pathogen-associated molecules. We examined individual roles for Toll-like receptors (TLRs)-7 and -8 in human NK-cell activation using synthetic, small molecule agonists of either TLR-7 (imiquimod and 3M-001), TLR-8 (3M-002) or both TLR-7/8 (3M-003 and R-848) for comparison with known ligands of TLR-2 to -9. Tracking cytokine production in PBMC initially revealed that a subset of TLR agonists including polyinosinic-polycytidylic acid (poly I:C), 3M-002, 3M-003, R-848 and single-stranded RNA trigger relatively high levels of IFN-gamma expression by NK cells. Isolated NK cells did not express TLR-7 or TLR-8. Unlike MALP-2 and poly I:C, 3M-001-3 did not induce expression of either CD69 or IFN-gamma by purified NK cells suggesting indirect activation. IL-18 and IL-12p70 were primarily required for induction of IFN-gamma by both synthetic and natural TLR-8 ligands, while type I IFN was required for induction of CD69 on NK cells by the TLR-7 agonist 3M-001. In addition to expression of IFN-gamma and CD69, relative induction of NK-cell cytotoxicity by TLR-7 and TLR-8 agonists was compared. Immune response modifiers (IRMs) with a TLR-8 agonist component (3M-002 and 3M-003) stimulated greater levels of K562 cytolysis than achieved with 3M-001 or IL-2 (1000 units ml(-1)). In vivo NK-cell cytotoxicity was also enhanced by R-848, but not in type I IFNR-deficient mice. We conclude that IRMs can modulate NK-cell function both in vitro and in vivo and that distinct indirect pathways control human NK-cell activation by TLR-7 and TLR-8 agonists.

MeSH terms

  • Animals
  • Antigens, CD / immunology
  • Antigens, Differentiation, T-Lymphocyte / immunology
  • Cytokines / immunology
  • Humans
  • Imidazoles / pharmacology
  • Interferon Inducers / pharmacology*
  • K562 Cells
  • Killer Cells, Natural / immunology*
  • Lectins, C-Type
  • Ligands
  • Lymphocyte Activation / drug effects*
  • Lymphocyte Activation / immunology
  • Mice
  • Mice, Mutant Strains
  • Quinolines / pharmacology
  • Receptors, Interferon / immunology
  • Signal Transduction / drug effects*
  • Toll-Like Receptor 7 / agonists*
  • Toll-Like Receptor 7 / immunology
  • Toll-Like Receptor 8 / agonists*
  • Toll-Like Receptor 8 / immunology


  • 3M 002
  • Antigens, CD
  • Antigens, Differentiation, T-Lymphocyte
  • CD69 antigen
  • Cytokines
  • Imidazoles
  • Interferon Inducers
  • Lectins, C-Type
  • Ligands
  • Quinolines
  • Receptors, Interferon
  • TLR7 protein, human
  • TLR8 protein, human
  • Toll-Like Receptor 7
  • Toll-Like Receptor 8