Recognition of Borrelia burgdorferi, the Lyme disease spirochete, by TLR7 and TLR9 induces a type I IFN response by human immune cells

J Immunol. 2009 Oct 15;183(8):5279-92. doi: 10.4049/jimmunol.0901390. Epub 2009 Sep 30.


Borrelia burgdorferi is the spirochetal agent of Lyme disease, a multisystemic disorder characterized by inflammation. Using global transcriptional profiling, we characterized the response of human PBMCs exposed to B. burgdorferi in an ex vivo coculture system. The expression profiles induced by B. burgdorferi were marked by the intense up-regulation of IFN-responsive transcripts and transcripts involved in the JAK/STAT signaling pathway. Transcript levels of IFN-alpha, IFN-beta, and IRF7, and protein concentrations of IFN-alpha, were significantly elevated relative to those in unstimulated PBMCs. The induction of IFN-alpha was completely dependent upon phagocytosis of B. burgdorferi. Addition of a soluble type I IFN receptor, B18R, did not abolish the induction of IFN-inducible genes, indicating that B. burgdorferi directly elicits enhanced expression of these genes independently of type I IFN feedback signaling. Inhibitors of either TLR7 or TLR9 significantly reduced B. burgdorferi-stimulated IFN-alpha protein expression and transcription of IFN-induced genes. Simultaneous inhibition of both TLR7 and TLR9 completely abrogated IFN-alpha induction. The IFN-alpha-producing populations in PBMCs were identified as plasmacytoid dendritic and CD14(+)CD11c(+) cells. These results reveal a TLR7/9-dependent signaling pathway used by human PBMCs to initiate a type I IFN response to the extracellular bacterium B. burgdorferi.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aminoquinolines / pharmacology
  • Borrelia burgdorferi / immunology*
  • Cells, Cultured
  • Gene Expression Profiling
  • Humans
  • Imiquimod
  • Interferon Inducers / pharmacology
  • Interferon Regulatory Factor-7 / immunology
  • Interferon Regulatory Factor-7 / metabolism
  • Interferon Type I / immunology*
  • Interferon Type I / metabolism
  • Leukocytes, Mononuclear / drug effects
  • Leukocytes, Mononuclear / immunology*
  • Leukocytes, Mononuclear / metabolism
  • Leukocytes, Mononuclear / microbiology
  • Lyme Disease / immunology*
  • Lyme Disease / microbiology
  • Oligodeoxyribonucleotides / pharmacology
  • Phagocytosis / drug effects
  • Phagocytosis / immunology
  • Signal Transduction / drug effects
  • Signal Transduction / immunology
  • Toll-Like Receptor 7 / antagonists & inhibitors
  • Toll-Like Receptor 7 / immunology*
  • Toll-Like Receptor 7 / metabolism
  • Toll-Like Receptor 9 / antagonists & inhibitors
  • Toll-Like Receptor 9 / immunology*
  • Toll-Like Receptor 9 / metabolism


  • Aminoquinolines
  • IRF7 protein, human
  • Interferon Inducers
  • Interferon Regulatory Factor-7
  • Interferon Type I
  • Oligodeoxyribonucleotides
  • TLR7 protein, human
  • TLR9 protein, human
  • Toll-Like Receptor 7
  • Toll-Like Receptor 9
  • Imiquimod