Monocyte chemoattractant protein-1 increases microglial infiltration and aggressiveness of gliomas.

Macrophages are thought to represent a first line of defense in anti-tumor immunity. Despite infiltration by microglial cells, however, malignant gliomas are still highly aggressive tumors. We here identify monocyte chemoattractant protein-1 (MCP-1) as a critical chemoattractant for glioma-infiltrating microglial cells. MCP-1-transfected rat CNS-1 gliomas were massively infiltrated by microglial cells. Whereas MCP-1 did not promote the growth of CNS-1 cells in vitro, intracerebral CNS-1-transfected tumors grew more aggressively than control-transfected tumors. This provides the first functional evidence that MCP-1 recruits microglial cells to gliomas and promotes their growth in vivo. Microglial cells may support rather than suppress glioma growth.