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Updated: Aug 20, 2026
Isolation and Culture of Bone Marrow-Derived Macrophages from Mice
Published on: June 23, 2023
Origin of macrophages in a kaolin-induced model of rat syringomyelia: a study using radiation bone marrow chimeras
Gabriel Yin Foo Lee1, Nigel Robert Jones, Graham Mayrhofer
1Department of Neurosurgery, University of Adelaide, Royal Adelaide Hospital, Adelaide, South Australia. gabriellee@ozemail.com.au
Study Design:
Animal experimental study.
Objective:
To study the origin of macrophages in a rat model of syringomyelia.
Summary Of Background Data:
Syringomyelia is a clinically important condition in which a cystic cavity forms within the spinal cord. This leads to significant delayed neurologic deterioration, which may be manifested as weakness, numbness, or pain. The pathophysiology and mechanism of syrinx formation remain unclear. Human autopsy findings have demonstrated a prominent accumulation of macrophages in relation to the syrinx. Similar observations have also been made in a previously established rat model of syringomyelia. Little is known about the origin and precise functions of these cells.
Methods:
Syrinx formation was induced by intraparenchymal injections of kaolin within the cervical spinal cords of 30 DA rat (RT7.1) radiation bone marrow chimeras reconstituted with bone marrow from RT7.2 congeneic donors. The distribution of macrophages was evaluated at survival times of 3 days, 1 week, and 4 weeks. Immunostaining of fresh-frozen spinal cord tissue was performed using specific antibodies against rat macrophage ED1 antigen and RT7.2 allele of CD45. This allowed donor-derived hematogenous (ED1+, RT7.2+) macrophages to be distinguished from native cells (ED1+, RT7.2-).
Results:
Central canal dilatation was seen from 1 week. This was associated with extensive accumulation of ED1+ macrophages within the spinal cord parenchyma. A large influx of bone marrow-derived (ED1+, RT7.2+) macrophages was observed. However, a considerable proportion of resident microglia (RT7.2-) also upregulated ED1. These activated microglia demonstrated distinct morphologic features.
Conclusions:
Large numbers of macrophages were recruited from the bone marrow in kaolin-induced rat syringomyelia. However, a significant number of resident microglia upregulated their ED1 activity and appear to provide a substantial source of macrophages.
Insights
In a rat model of syringomyelia, both bone marrow-derived cells and resident microglia contribute to the macrophage population. This finding sheds light on the cellular origins of spinal cord inflammation in this condition.
Area of Science:
- Neuroscience
- Immunology
- Pathology
Background:
- Syringomyelia involves spinal cord cyst formation leading to neurological decline.
- The exact mechanisms and cellular players in syrinx development are not fully understood.
- Macrophages are known to accumulate in syringomyelia, but their origin and role are unclear.
Purpose of the Study:
- To investigate the cellular origin of macrophages in a rat model of kaolin-induced syringomyelia.
- To differentiate between bone marrow-derived and resident cells contributing to the macrophage pool.
Main Methods:
- Kaolin was injected into the cervical spinal cords of rat bone marrow chimeras.
- Rats were analyzed at 3 days, 1 week, and 4 weeks post-injection.
- Immunostaining identified donor-derived (hematogenous) and native (microglia) macrophages using ED1 and RT7.2 markers.
Main Results:
- Central canal dilatation and macrophage accumulation were observed starting at 1 week.
- A significant influx of bone marrow-derived macrophages (ED1+, RT7.2+) was detected.
- Resident microglia (RT7.2-) also upregulated ED1, indicating activation and contribution to the macrophage population.
Conclusions:
- Kaolin-induced syringomyelia in rats involves recruitment of macrophages from the bone marrow.
- Resident microglia significantly contribute to the macrophage population by upregulating ED1.
- Both extrinsic and intrinsic cells play a role in the inflammatory response in syringomyelia.
