Sequence-dependent stimulation of the mammalian innate immune response by synthetic siRNA

Nat Biotechnol. 2005 Apr;23(4):457-62. doi: 10.1038/nbt1081. Epub 2005 Mar 20.


Short interfering RNAs (siRNAs) that mediate specific gene silencing through RNA interference (RNAi) are widely used to study gene function and are also being developed for therapeutic applications. Many nucleic acids, including double- (dsRNA) and single-stranded RNA (ssRNA), can stimulate innate cytokine responses in mammals. Despite this, few studies have questioned whether siRNA may have a similar effect on the immune system. This could significantly influence the in vivo application of siRNA owing to off-target effects and toxicities associated with immune stimulation. Here we report that synthetic siRNAs formulated in nonviral delivery vehicles can be potent inducers of interferons and inflammatory cytokines both in vivo in mice and in vitro in human blood. The immunostimulatory activity of formulated siRNAs and the associated toxicities are dependent on the nucleotide sequence. We have identified putative immunostimulatory motifs that have allowed the design of siRNAs that can mediate RNAi but induce minimal immune activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence*
  • Cell Culture Techniques
  • Cells, Cultured
  • Dendritic Cells / immunology
  • Enzyme-Linked Immunosorbent Assay
  • Humans
  • Immunity, Innate / drug effects*
  • Interferon-alpha / analysis
  • Interferon-gamma / analysis
  • Interleukin-6 / analysis
  • Leukocytes, Mononuclear / cytology
  • Leukocytes, Mononuclear / drug effects*
  • Leukocytes, Mononuclear / immunology
  • Lipopolysaccharide Receptors / immunology
  • Liposomes
  • Mice
  • Mice, Inbred A
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Mice, Inbred ICR
  • RNA Interference
  • RNA, Small Interfering / biosynthesis*
  • RNA, Small Interfering / chemistry*
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / pharmacology*
  • Tumor Necrosis Factor-alpha / analysis


  • Interferon-alpha
  • Interleukin-6
  • Lipopolysaccharide Receptors
  • Liposomes
  • RNA, Small Interfering
  • Tumor Necrosis Factor-alpha
  • Interferon-gamma