The generation of macrophages from precursor cells incubated with brain endothelial cells--a release of CSF-1 like factor from endothelial cells.

The perivascular macrophages in the brain are thought to be derived from bone marrow precursor cells. Results presented here demonstrate that immature macrophages obtained from nonadherent spleen cell populations can adhere to cerebrovascular endothelial cell (EC) monolayers and proliferate. The proliferation of these cells can be stimulated by either purified murine granulocyte-macrophage colony-stimulating factor (GM-CSF) or EC conditioned medium but not by IL-3. No proliferation of the GM-CSF- or IL-3-dependent murine cell line IC-2 was observed in the presence of EC conditioned medium. Macrophage-like cells could also be derived from murine bone marrow cells but inhibited by anti-macrophage-CSF (M-CSF or CSF-1). The capacity of EC conditioned medium to induce the proliferation of macrophage-like cells from the spleen is therefore not due to the release of GM-CSF but CSF-1. In concomitant experiments using mature macrophages incubated on EC monolayers, no proliferation was observed. These findings suggest that the growth of perivascular macrophages in the brain may be stimulated by cerebrovascular EC.