Osteoclasts, mononuclear phagocytes, and c-Fos: New insight into osteoimmunology

Koichi Matsuo, Neelanjan Ray

Research output: Contribution to journalReview articlepeer-review

44 Citations (Scopus)


Osteoimmunology is the emerging concept that certain molecules link the skeletal and immune systems. The transcription factor c-Fos, a component of activator protein-1 (AP-1), is essential for osteoclast differentiation. Mice lacking c-Fos are osteopetrotic owing to impaired osteoclast development. Recent studies suggest that in contrast to this positive role in osteoclastogenesis, c-Fos expression inhibits differentiation and activation of mononuclear phagocytes. Here, we focus on the contrasting roles of c-Fos in the bone and immune lineages. Both osteoclasts and mononuclear phagocytes are derived from common myeloid precursors. Osteoclasts resorb bone, whereas macrophages and myeloid dendritic cells phagocytose microbial pathogens, initiating innate and adaptive immunity. Differentiation of the common precursors into either bone or immune lineage is determined by ligand binding to cell-surface receptors, particularly receptor activator of NF-κB (RANK) for osteoclasts, or Toll-like receptors (TLRs) for mononuclear phagocytes. Both RANK and TLRs activate the dimeric transcription factors NF-κB and AP-1. Yet, c-Fos/AP-1 plays a positive role in osteoclasts but a negative role in macrophages and dendritic cells. Further study is necessary to clarify this dual role of c-Fos.

Original languageEnglish
Pages (from-to)78-84
Number of pages7
JournalKeio Journal of Medicine
Issue number2
Publication statusPublished - 2004 Jun


  • AP-1
  • Dendritic cell
  • Macrophage
  • Osteoclast
  • c-Fos

ASJC Scopus subject areas

  • General Medicine


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