Monocyte chemoattractant protein–1 increases microglial infiltration and aggressiveness of gliomas

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Abstract
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.