TLR7 is involved in sequence-specific sensing of single-stranded RNAs in human macrophages.
Human TLR7 and 8 (hTLR7/8) have been implicated in the sequence-dependent detection of RNA oligonucleotides in immune cells. Although hTLR7 sequence-specific sensing of short RNAs has been inferred from studies of murine TLR7, this has yet to be established for hTLR7. We found that different short ssRNA sequences selectively induced either TNF-alpha or IFN-alpha in human PBMCs. The sequence-specific TNF-alpha response to ssRNAs observed in PBMCs could be replicated in activated human macrophage-like (THP-1) cells pretreated with IFN-gamma. Surprisingly, suppression of hTLR7 expression by RNA interference in this model reduced sensing of all immunostimulatory ssRNAs tested. Modulation of the relative expression ratio of hTLR7 to hTLR8 in THP-1 cells correlated with differential sensing of immunostimulatory sequences. Furthermore, the sequence-specific IFN-alpha induction profile in human PBMCs was accurately modeled by a sequence-specific activation of murine TLR7 in mouse macrophages. Thus, we demonstrate for the first time that hTLR7 is involved in sequence-specific sensing of ssRNAs. We establish a novel cell model for the prediction of TNF-alpha induction by short RNAs in human macrophages. Our results suggest that differential sequence-specific sensing of RNA oligonucleotides between human and mouse macrophages is due to the modulation of TLR7 sensing by human TLR8.
Gantier
Michael P
MP
Centre for Cancer Research, Monash Institute of Medical Research, Monash University, 246 Clayton Road, Clayton, Victoria 3168, Australia.
Tong
Stephen
S
Behlke
Mark A
MA
Xu
Dakang
D
Phipps
Simon
S
Foster
Paul S
PS
Williams
Bryan R G
BR
D000276:Adjuvants, Immunologic / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D006801:Humans; D016898:Interferon-alpha / Q000096:biosynthesis; D008264:Macrophages / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D035683:MicroRNAs / Q000032:analysis* / Q000378:metabolism* / Q000502:physiology; D051199:Toll-Like Receptor 7 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051200:Toll-Like Receptor 8 / Q000096:biosynthesis / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D020298:U937 Cells
D000276:Adjuvants, Immunologic; D016898:Interferon-alpha; D035683:MicroRNAs; C495348:TLR7 protein, human; C495349:TLR8 protein, human; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; D014409:Tumor Necrosis Factor-alpha