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Updated: Jun 8, 2026
Tracking Mouse Bone Marrow Monocytes In Vivo
Published on: February 27, 2015
On the use of micron-sized iron oxide particles (MPIOS) to label resting monocytes in bone marrow
Kevin S Tang1, Bradley Hann, Erik M Shapiro
1Department of Biomedical Engineering, Yale University School of Medicine, New Haven, CT, USA.
Purpose:
The use of MRI to monitor immune cell infiltration into various pathologies is well established. In an effort to boost the magnetic material within immune cells, this work attempted to label resting monocytes within bone marrow, in mice, by intravenous administration of micron-sized iron oxide particles (MPIOs), similar in fashion to the administration of (U)SPIO.
Procedures:
MPIOs were incubated with various immune cells both in culture, and in whole blood. Flow cytometry and histology were used to analyze magnetic cell labeling. Also, MPIOs were injected intravenously into mice. In vivo, high-resolution 3-D MRI was performed on mouse legs, and signal changes were quantified. Flow cytometry and histology were used to analyze magnetic cell labeling of bone marrow resident cells.
Results:
It is demonstrated here that monocytes and neutrophils can indeed endocytose MPIOs both in cell culture and ex vivo in whole blood. However, despite rapid accumulation of MPIOs within the bone marrow following injection, MPIOs did not label monocytes or any other hematopoietic cell type in the marrow. Hypotheses are drawn to explain these results in light of recent usage of MPIOs for immune cell tracking.
Conclusions:
Systemic administration of various MPIO formulations showed that MPIOs arrive in bone marrow rapidly following injection and remain there for at least 7 days. Data also shows slow clearance of some particles from the tissue over this period. While MPIOs can efficiently label monocytes in culture and in whole blood ex vivo, they were not found to label bone marrow resident monocytes.
Insights
Micron-sized iron oxide particles (MPIOs) can label monocytes in culture but fail to label bone marrow monocytes in vivo. This study investigates MPIOs for immune cell tracking in mice.
Area of Science:
- Biomedical imaging
- Immunology
- Nanotechnology
Background:
- Magnetic Resonance Imaging (MRI) is used to track immune cells in diseases.
- Micron-sized iron oxide particles (MPIOs) are investigated for enhanced magnetic labeling of immune cells.
- Previous studies utilized (U)SPIO for similar applications.
Purpose of the Study:
- To assess the efficacy of intravenously administered MPIOs in labeling bone marrow resident monocytes in mice.
- To evaluate the potential of MPIOs as a tool for in vivo immune cell tracking.
Main Methods:
- MPIOs were incubated with immune cells in culture and whole blood.
- Flow cytometry and histology were used to analyze cell labeling.
- In vivo MRI was performed on mouse legs after MPIO injection.
- Bone marrow cells were analyzed for MPIO labeling.
Main Results:
- Monocytes and neutrophils successfully endocytosed MPIOs in vitro and ex vivo.
- MPIOs rapidly accumulated in bone marrow post-injection.
- No labeling of bone marrow monocytes or other hematopoietic cells by MPIOs was observed in vivo.
- MPIOs remained in bone marrow for at least 7 days with slow clearance.
Conclusions:
- Systemic MPIO administration leads to rapid bone marrow accumulation.
- Despite in vitro labeling capability, MPIOs do not label bone marrow monocytes in vivo.
- Further research is needed to understand the in vivo labeling limitations of MPIOs for immune cell tracking.
