Amplification of the response to Toll-like receptor ligands by prolonged exposure to interleukin-6 in mice: implication for the pathogenesis of macrophage activation syndrome

Arthritis Rheum. 2012 May;64(5):1680-8. doi: 10.1002/art.33496.


Objective: To investigate whether prolonged exposure to interleukin-6 (IL-6) affects the inflammatory response induced by Toll-like receptor (TLR) ligands.

Methods: IL-6-transgenic mice and wild-type mice were stimulated with different TLR ligands; survival rates, blood cell counts, and biochemical parameters were analyzed. Murine splenic mononuclear cells and peritoneal macrophages were stimulated with lipopolysaccharide (LPS), lipoteichoic acid, poly(I-C), or CpG. Human macrophages were cultured for 4 days in the presence of IL-6 and then stimulated with LPS. Inflammatory cytokine expression was measured by enzyme-linked immunosorbent assay or reverse transcription-polymerase chain reaction. Activation of STAT-3, ERK-1/2 (MAPK), and p65 NF-κB was evaluated by Western blotting or confocal analysis.

Results: Treatment of IL-6-transgenic mice with TLR ligands led to an increased fatality rate and elevated levels of IL-1β, tumor necrosis factor α (TNFα), IL-6, and IL-18. Macrophages from IL-6-transgenic mice produced increased levels of inflammatory cytokines, which were associated with increased phosphorylation of STAT-3 and ERK-1/2 and with increased NF-κB nuclear translocation. Human macrophages treated with IL-6 and then stimulated with LPS showed elevated levels of cytokines and similarly elevated signaling pathway activation. After LPS administration, IL-6-transgenic mice showed an increase in ferritin and soluble CD25 levels, as well as a decrease in platelet and neutrophil counts and in hemoglobin levels compared to wild-type mice.

Conclusion: Our findings indicate that prolonged exposure to IL-6 in vivo and in vitro leads to an exaggerated inflammatory response to TLR ligands. Hematologic and biochemical abnormalities in IL-6-transgenic mice treated with LPS show striking similarities to macrophage activation syndrome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biomarkers / metabolism
  • Cytokines / metabolism
  • Disease Models, Animal
  • Hematologic Tests
  • Humans
  • Interleukin-6 / pharmacology*
  • Leukocytes, Mononuclear / drug effects
  • Leukocytes, Mononuclear / metabolism
  • Ligands
  • Lipopolysaccharides / immunology
  • Longevity / drug effects
  • Macrophage Activation Syndrome / immunology
  • Macrophage Activation Syndrome / metabolism*
  • Macrophage Activation Syndrome / pathology
  • Macrophages, Peritoneal / drug effects
  • Macrophages, Peritoneal / metabolism
  • Mice
  • Mice, Transgenic
  • Spleen / metabolism
  • Toll-Like Receptors / agonists
  • Toll-Like Receptors / metabolism*


  • Biomarkers
  • Cytokines
  • Interleukin-6
  • Ligands
  • Lipopolysaccharides
  • Toll-Like Receptors