CCL2 and colitis: CCL2 induced infiltration of regulatory dendritic cells and regulatory T cells in the tumor microenvironment [33], CXCL5/CXCR2 axis mediates the accumulation of CXCR2+ MDSCs [34], CXCR2−/− mice were resistance to colitis-associated cancer formation by inhibiting MDSCs accumulation in the mucosa [15], and silence of CXCL1/2 expression in breast cancer decreased the infiltration of myeloid cells in the tumor microenvironment [17].