Embryonic CNS macrophages and microglia do not stem from circulating, but from extravascular precursors

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H Kurz1, B Christ

  • 1Anatomisches Institut II der Universität, Freiburg, Germany.

Glia
|January 22, 1998
PubMed

Insights

Avian microglia precursors do not enter the embryonic central nervous system (CNS) via blood vessels. Instead, macrophages invade from the pial surface to generate CNS microglia.

Area of Science:

  • Developmental biology
  • Neuroscience
  • Immunology

Background:

  • Mesoderm-derived cells form early central nervous system (CNS) macrophage and microglia populations in avian embryos.
  • Proposed entry routes include CNS blood vessels, ventricular cavities, and the pial surface.
  • Invasion of circulating blood cells into the embryonic CNS has not been definitively proven.

Purpose of the Study:

  • To investigate the origin of embryonic CNS microglia in avian embryos.
  • To determine if circulating blood cells contribute to the CNS macrophage and microglia populations.
  • To elucidate the primary route of entry for microglia precursors into the developing CNS.

Main Methods:

  • Creation of chick-quail blood chimeras using parabiosis (two embryos sharing a single egg).
  • Utilized the QH1 monoclonal antibody to detect and track quail cells within chick blood vessels.
  • Examined the presence of extravascular QH1-positive cells (macrophages) in the CNS of parabiosis embryos.

Main Results:

  • QH1-positive cells (quail macrophages) were identified in the CNS of parabiosis quail embryos (E7-10).
  • QH1-positive cells were notably absent in the CNS of parabiosis chick embryos.
  • No evidence of quail cells penetrating the endothelial wall of CNS blood vessels was observed.

Conclusions:

  • Avian macrophages/microglia precursors do not infiltrate the embryonic CNS by crossing the walls of CNS blood vessels.
  • The findings strongly support the hypothesis that macrophages migrate from the pial surface into the CNS.
  • Proliferation of these invading macrophages within the CNS is the primary mechanism generating microglia in avian embryos.

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