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Macrophages in the central nervous system of the rat
Abstract:
In an immunohistochemical study using monoclonal antibodies, which exclusively recognize cells of the monocyte-macrophage lineage, and monoclonal antibodies against the Ia-antigen, we describe the occurrence of macrophages in the developing and adult central nervous system (CNS). In normal adult brain, no macrophages could be detected in the CNS parenchyma; only in the meninges and the choroid plexes were a few macrophages found. During ontogeny, numerous phagocytic cells infiltrated the CNS parenchyma; these cells which did not express Ia are blood-borne. About three weeks after birth, all macrophages had disappeared from the CNS. As microglia in adult and developing brain do not stain with the anti-macrophage antibodies, we suggest that microglial cells are not related to the mononuclear phagocyte system and do not have a hematogenous origin.
Insights
Macrophages are absent in the adult central nervous system (CNS) parenchyma. Developing CNS contains blood-borne phagocytic cells, but not microglia, suggesting microglia are not of monocyte-macrophage origin.
Area of Science:
- Neuroscience
- Immunology
- Developmental Biology
Background:
- The central nervous system (CNS) has unique immune surveillance mechanisms.
- The origin and identity of resident immune cells, like microglia, remain debated.
- Understanding CNS immune cell origins is crucial for neuroinflammatory and neurodegenerative disease research.
Purpose of the Study:
- To investigate the presence and origin of macrophages within the developing and adult CNS.
- To determine if microglia are derived from the mononuclear phagocyte system.
- To differentiate between blood-borne macrophages and resident microglia in the CNS.
Main Methods:
- Immunohistochemical analysis using monoclonal antibodies specific to the monocyte-macrophage lineage.
- Use of monoclonal antibodies against the Ia-antigen (MHC class II).
- Comparative analysis of cell populations in developing versus adult CNS parenchyma, meninges, and choroid plexuses.
Main Results:
- No macrophages were detected in the normal adult CNS parenchyma; few were found in meninges and choroid plexes.
- Numerous blood-borne, Ia-negative phagocytic cells infiltrated the CNS parenchyma during development (ontogeny).
- These infiltrating cells disappeared from the CNS approximately three weeks after birth.
- Microglia in both developing and adult brain did not react with anti-macrophage antibodies.
Conclusions:
- Microglial cells in the adult and developing brain are distinct from cells of the mononuclear phagocyte system.
- Microglia do not appear to have a hematogenous origin.
- The study suggests microglia are resident CNS cells, not derived from circulating monocytes or macrophages.