Myeloid differentiation factor-88 (MyD88) is essential for control of primary in vivo Francisella tularensis LVS infection, but not for control of intra-macrophage bacterial replication

Microbes Infect. 2006 Mar;8(3):779-90. doi: 10.1016/j.micinf.2005.09.014. Epub 2006 Jan 18.


The means by which Francisella tularensis, the causative agent of tularemia, are recognized by mammalian immune systems are poorly understood. Here we wished to explore the contribution of the MyD88/Toll-like receptor signaling pathway in initiating murine responses to F. tularensis Live Vaccine Strain (LVS). MyD88 knockout (KO) mice, but not TLR2-, TLR4- or TLR9-deficient mice, rapidly succumbed following in vivo bacterial infection via the intradermal route even with a very low dose of LVS (5 x 10(1)) that was 100,000-fold less than the LD(50) of normal wild-type (WT) mice. By day 5 after LVS infection, bacterial organ burdens were 5-6 logs higher in MyD88 knockout mice; further, unlike infected WT mice, levels of interferon-gamma in the sera of LVS-infected MyD88 KO were undetectable. An in vitro culture system was used to assess the ability of bone marrow macrophages derived from either KO or WT mice to support bacterial growth, or to control intracellular bacterial replication when co-cultured with immune lymphocytes. In this assay, bacterial replication was similar in macrophages derived from either WT or any of the TLR KO mice. Bacterial growth was controlled in co-cultures containing macrophages from MyD88 KO mice or TLR KO mice as well as in co-cultures containing immune WT splenic lymphocytes and WT macrophages. Further, MyD88-deficient LVS-immune splenocytes controlled intracellular growth comparably to those from normal mice. Thus MyD88 is essential for innate host resistance to LVS infection, but is not required for macrophage control of intracellular bacterial growth.

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • Bone Marrow Cells / metabolism
  • Bone Marrow Cells / microbiology
  • Francisella tularensis / metabolism*
  • Interleukin-1 / metabolism
  • Interleukin-18 / metabolism
  • Macrophages / metabolism
  • Macrophages / microbiology*
  • Mice
  • Mice, Knockout
  • Myeloid Differentiation Factor 88
  • Signal Transduction
  • Toll-Like Receptor 2 / genetics
  • Toll-Like Receptor 2 / metabolism
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism
  • Toll-Like Receptor 9 / metabolism


  • Adaptor Proteins, Signal Transducing
  • Interleukin-1
  • Interleukin-18
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • Tlr2 protein, mouse
  • Tlr4 protein, mouse
  • Tlr9 protein, mouse
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • Toll-Like Receptor 9