Perivascular location and phenotypic heterogeneity of microglial cells in the rat brain.

Employing immunohistochemical techniques and a panel of monoclonal antibodies that recognize rat cells of monocyte/macrophage lineage, we have demonstrated that cells labeled with these antibodies are widely distributed throughout the parenchyma of the rat brain. These cells have a remarkable microglial morphology and form phenotypically heterogenous populations. Double immunoperoxidase staining with the monoclonal antibody and anti-von Willebrand factor antiserum, which recognizes vascular endothelial cells, revealed that these cells are located exclusively at perivascular sites in the adult brain. These observations indicate that the microglial cells are perivascular cells of the monocyte/macrophage lineage, and may be intimately involved in various immunopathogenic conditions of the central nervous system.