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CFU-rAM, the origin of lung macrophages, and the macrophage lineage
S P Sorokin1, N A McNelly, R F Hoyt
1Department of Anatomy and Neurobiology, Boston University School of Medicine, Massachusetts 02118.
Abstract:
Macrophage precursors and their progeny have been identified in early rat embryos with the use of a peroxidase-coupled marker, isolectin B4 of Griffonia simplicifolia (GSA I-B4). The macrophage lineage can be traced back to actively dividing GSA-positive angular cells present in the mesenchyme of late neurulas. These increase in number and establish residence successively in rudiments of the central nervous system, liver, and lungs. In organ-cultured fetal lungs they transform directly into a self-replicating population of macrophages responsive to colony-stimulating factors. The angular cell therefore can be seen as the source of lung macrophages during prenatal life. The extent to which this manner of production continues in postnatal life is unclear, but it appears that central hematopoietic tissues (bone marrow, spleen) may generate macrophages by a direct pathway from early-committed progenitors as well as indirectly through a series of intermediate stem cells. Considering the wealth of new information available from diverse studies in specialized culture environments and to a lesser extent from studies in vivo, it is time to integrate these findings into a more comprehensive theory of macrophage origin and fate than we have at present.
Insights
Researchers identified macrophage precursors in early rat embryos using isolectin B4 of Griffonia simplicifolia (GSA I-B4). These precursors, originating from angular cells, populate various organs, offering insights into macrophage development and origins.
Area of Science:
- Developmental Biology
- Immunology
- Hematopoiesis
Background:
- Macrophages are crucial immune cells with diverse roles.
- Understanding their origin is key to developmental and immunological research.
- Previous studies have offered fragmented insights into macrophage development.
Purpose of the Study:
- To trace the origin and developmental pathway of macrophage precursors in early rat embryos.
- To identify specific precursor cells and their migratory routes.
- To integrate current findings into a comprehensive theory of macrophage ontogeny.
Main Methods:
- Utilized a peroxidase-coupled marker, Griffonia simplicifolia isolectin B4 (GSA I-B4), to identify macrophage precursors.
- Employed organ culture of fetal lungs to study macrophage transformation.
- Integrated data from in vivo studies and specialized culture environments.
Main Results:
- Macrophage precursors, identified as GSA I-B4-positive angular cells, were found in the mesenchyme of late neurula-stage rat embryos.
- These precursors migrate to and populate the central nervous system, liver, and lungs.
- In fetal lungs, these cells differentiate into self-replicating macrophages responsive to colony-stimulating factors, indicating they are a primary source of prenatal lung macrophages.
Conclusions:
- The angular cell is identified as the source of lung macrophages during prenatal development.
- Postnatal macrophage generation may involve direct pathways from committed progenitors and indirect routes via stem cells in hematopoietic tissues.
- A comprehensive theory integrating diverse findings on macrophage origin and fate is needed.