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Updated: Feb 24, 2026
Experimental Analysis of Apoptotic Thymocyte Engulfment by Macrophages
Published on: May 24, 2019
T Cell Zone Resident Macrophages Silently Dispose of Apoptotic Cells in the Lymph Node
Myriam Baratin1, Léa Simon1, Audrey Jorquera1
1Aix Marseille Univ, CNRS, INSERM, CIML, Marseille, France.
Abstract:
In lymph nodes (LNs), dendritic cells (DCs) are thought to dispose of apoptotic cells, a function pertaining to macrophages in other tissues. We found that a population of CX3CR1+ MERTK+ cells located in the T cell zone of LNs, previously identified as DCs, are efferocytic macrophages. Lineage-tracing experiments and shield chimeras indicated that these T zone macrophages (TZM) are long-lived macrophages seeded in utero and slowly replaced by blood monocytes after birth. Imaging the LNs of mice in which TZM and DCs express different fluorescent proteins revealed that TZM-and not DCs-act as the only professional scavengers, clearing apoptotic cells in the LN T cell zone in a CX3CR1-dependent manner. Furthermore, similar to other macrophages, TZM appear inefficient in priming CD4 T cells. Thus, efferocytosis and T cell activation in the LN are uncoupled processes designated to macrophages and DCs, respectively, with implications to the maintenance of immune homeostasis.
Insights
Previously identified dendritic cells in lymph nodes are actually macrophages. These T zone macrophages (TZM) clear apoptotic cells, a role separate from T cell activation by dendritic cells, maintaining immune homeostasis.
Area of Science:
- Immunology
- Cell Biology
- Histology
Background:
- Dendritic cells (DCs) in lymph nodes (LNs) were thought to clear apoptotic cells.
- This efferocytic function is typically performed by macrophages in other tissues.
Purpose of the Study:
- To identify the specific cell type responsible for efferocytosis in the T cell zone of LNs.
- To elucidate the distinct roles of macrophages and DCs in LN immune functions.
Main Methods:
- Lineage-tracing experiments in mice.
- Shield chimera models.
- Fluorescent protein imaging of LNs.
- CX3CR1 expression analysis.
Main Results:
- A population of CX3CR1+ MERTK+ cells in the LN T cell zone, previously identified as DCs, are identified as efferocytic macrophages.
- These T zone macrophages (TZM) are long-lived, originating in utero and slowly replaced by monocytes postnatally.
- TZM, not DCs, are the primary scavengers of apoptotic cells in the LN T cell zone via a CX3CR1-dependent mechanism.
- TZM are inefficient at priming CD4 T cells.
Conclusions:
- Efferocytosis and T cell activation in LNs are distinct functions performed by macrophages and DCs, respectively.
- This functional uncoupling is crucial for maintaining immune homeostasis within the lymph nodes.
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