CX3CR1 and central nervous system cancer: Since Cx3cr1-deficient inflammatory monocytes and monocyte-derived macrophages express higher levels of IL1β compared to heterozygous Cx3cr1 and WT tumors, they induce increases in CCL2 expression by glioma cells, which in turn causes the recruitment of more CCR2-positive inflammatory monocytes into the tumor, as shown in Fig. 2A and 2B.