CCR2 and glioma: CCL20 secreted by glioma cells induces CCL2 secretion by peritumor microglia (PGAM) and attracts a variety of peripheral immunosuppressive cells via CCR2/4 to participate in the establishment of the immunosuppressive microenvironment of glioma, which includes MDSC (myeloid-derived suppressor cells) and Tregs (regulatory T cells) differentiated from monocytes (101).