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Updated: Mar 30, 2026
Bone Marrow-derived Macrophage Production
Published on: November 22, 2013
Macrophages: Their Emerging Roles in Bone
Benjamin P Sinder1, Allison R Pettit2, Laurie K McCauley1,3
1Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI, USA.
Abstract:
Macrophages are present in nearly all tissues and are critical for development, homeostasis, and regeneration. Resident tissue macrophages of bone, termed osteal macrophages, are recently classified myeloid cells that are distinct from osteoclasts. Osteal macrophages are located immediately adjacent to osteoblasts, regulate bone formation, and play diverse roles in skeletal homeostasis. Genetic or pharmacological modulation of macrophages in vivo results in significant bone phenotypes, and these phenotypes depend on which macrophage subsets are altered. Macrophages are also key mediators of osseous wound healing and fracture repair, with distinct roles at various stages of the repair process. A central function of macrophages is their phagocytic ability. Each day, billions of cells die in the body and efferocytosis (phagocytosis of apoptotic cells) is a critical process in both clearing dead cells and recruitment of replacement progenitor cells to maintain homeostasis. Recent data suggest a role for efferocytosis in bone biology and these new mechanisms are outlined. Finally, although macrophages have an established role in primary tumors, emerging evidence suggests that macrophages in bone support cancers which preferentially metastasize to the skeleton. Collectively, this developing area of osteoimmunology raises new questions and promises to provide novel insights into pathophysiologic conditions as well as therapeutic and regenerative approaches vital for skeletal health.
Insights
Osteal macrophages, distinct bone cells, regulate bone formation and repair. Their roles in skeletal health, healing, and cancer metastasis are crucial for understanding osteoimmunology and developing new therapies.
Area of Science:
- Osteoimmunology
- Skeletal Biology
- Cellular Biology
Background:
- Macrophages are vital immune cells found in all tissues, crucial for development, homeostasis, and regeneration.
- Osteal macrophages, a specific type residing in bone, are distinct from osteoclasts and regulate bone formation.
- These macrophages are involved in skeletal homeostasis, fracture repair, and potentially support bone metastasis of cancers.
Purpose of the Study:
- To review the diverse roles of osteal macrophages in bone biology.
- To highlight the importance of macrophage efferocytosis in bone homeostasis and repair.
- To discuss the emerging role of bone macrophages in skeletal cancer metastasis.
Main Methods:
- Literature review of current research on osteal macrophages.
- Analysis of genetic and pharmacological studies modulating macrophage function in vivo.
- Examination of studies investigating efferocytosis in bone and macrophage roles in skeletal pathologies.
Main Results:
- Osteal macrophages are key regulators of bone formation and skeletal homeostasis.
- Macrophage subsets play distinct roles in fracture repair.
- Efferocytosis by macrophages is critical for clearing apoptotic cells and progenitor cell recruitment in bone.
- Macrophages in bone may support the growth of cancers that metastasize to the skeleton.
Conclusions:
- Osteal macrophages are critical for skeletal health, influencing bone formation, regeneration, and repair.
- Understanding macrophage functions, including efferocytosis and roles in cancer, is vital for advancing osteoimmunology.
- Further research into osteal macrophages promises novel therapeutic and regenerative strategies for skeletal conditions.
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