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Endotoxin signaling in human macrophages: signaling via an alternate mechanism

Sandra M Sacre1, Evangelos Andreakos, Mark Feldmann

  • 1Kennedy Institute of Rheumatology Division, Faculty of Medicine, Imperial College of Science, Technology and Medicine, London, UK.

Journal of Endotoxin Research
|December 14, 2004
PubMed

Insights

Lipopolysaccharide (LPS) triggers inflammatory responses via Toll-like receptors (TLRs). Human macrophages utilize alternative pathways, unlike murine models, to activate NF-kappaB and release cytokines.

Area of Science:

  • Immunology
  • Cell Biology
  • Molecular Biology

Background:

  • Lipopolysaccharide (LPS) is a key trigger in sepsis, activating Toll-like receptors (TLRs) and leading to inflammatory cytokine release.
  • Signaling pathways, including MyD88, Mal/TIRAP, and IKK2, are known to induce NF-kappaB in cell lines and murine models.
  • Fundamental differences in LPS signaling exist between human and murine macrophages, and between myeloid and non-myeloid cells.

Purpose of the Study:

  • To investigate LPS-induced signaling pathways in primary human cells, focusing on myeloid and non-myeloid origins.
  • To elucidate the role of MyD88, Mal/TIRAP, and IKK2 in NF-kappaB activation in human macrophages.
  • To identify alternative signaling pathways independent of MyD88, Mal/TIRAP, and IKK2 in human macrophages.

Main Methods:

  • Utilized dominant-negative approaches in primary human cells due to the absence of knockouts.
  • Investigated signaling cascades in primary human macrophages and synovial fibroblasts.
  • Analyzed NF-kappaB activation and inflammatory cytokine expression.

Main Results:

  • Primary human macrophages activate NF-kappaB and induce inflammatory cytokines through MyD88, Mal/TIRAP, and IKK2-independent alternative pathways.
  • In contrast, non-myeloid synovial fibroblasts require MyD88 and/or Mal/TIRAP as essential adaptors for LPS signaling.
  • Demonstrated significant differences in LPS-induced signaling between human and murine macrophages.

Conclusions:

  • LPS signaling pathways exhibit fundamental differences between human and murine macrophages.
  • Human macrophages employ alternative pathways for NF-kappaB activation and cytokine induction, distinct from murine models.
  • MyD88 and/or Mal/TIRAP are crucial for LPS signaling in human non-myeloid cells, but not exclusively in macrophages.

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