CCL2 and central nervous system cancer: Importantly, this increase in migration in both IL-33 and ΔNLS CM could be reduced by neutralizing antibodies to IL-33 or CCL2 (Fig. 7b), a chemokine upregulated by rIL-33 similar to upregulation of chemokines in IL-33-expressing glioma cells or present in the tumor interstitial fluid (TIF) of IL-33-expressing tumors (Figs. 1d, 4c and 7c).