CCL2 and glioma: Analysis with the CGGA database (http://www.cgga.org.cn/) showed that CCL2 was significantly overexpressed in GBM among other histological types of brain tumors (Fig. 1A), and that its expression level was positively correlated with WHO grade of glioma (Fig. 1B), in which grade IV (GBM) displayed the highest level of CCL2, suggesting that CCL2 may be associated with malignant progression of glioma.