CCL2 and glioblastoma: The GBM microenvironment produces several factors, monocyte chemoattractant protein-1 (MCP-1/CCL2), colony-stimulating factor-1 (CSF-1), IL-10 and TGF-β, which polarize MΦs toward the pro-tumoral M2 phenotype while reducing the anti-tumoral M1 population.