Brain APCs including microglia are only differential and positional polymorphs.

Area of Science:

• Neuroimmunology
• Cell Biology
• Immunology

Background:

• Antigen presentation to lymphocytes in the brain was traditionally thought to involve distinct cell populations at different locations.
• Recent evidence suggests microglial cells can adopt dendritic cell phenotypes in response to pathogenic or cytokine-driven environments.

Purpose of the Study:

• To challenge the existing notion of distinct brain antigen-presenting cells (APCs).
• To propose that brain APCs with macrophage, microglia, or dendritic cell phenotypes originate from a common precursor population.
• To highlight the plasticity of these cells in response to microenvironmental cues.

Main Methods:

• Review of recent evidence on microglial cell phenotypes and myeloid lineage functions.
• In vitro transformation of monocytic precursor cells into microglial cells.
• In vivo transplantation studies to observe cell phenotypes.

Main Results:

• Microglial cells exhibit dendritic cell phenotypes in specific environments.
• Monocytic precursor cells can differentiate into cells with microglial phenotypes in vivo.
• These myeloid cells demonstrate interconvertibility between macrophage, microglia, and dendritic cell forms.
• Cellular maturation is influenced by microenvironmental cues.

Conclusions:

• Brain APCs appearing as macrophage, microglia, or dendritic cell forms are derivatives of the same myeloid precursor population.
• The observed phenotypes are a result of cellular plasticity influenced by location and microenvironment.
• Microglia are not distinct cell types, exhibiting plasticity from neonatal stages through adulthood.