CCL2 and colorectal carcinoma: LPS, a metabolite of E. coli, can induce M2 polarization of TAMs, thus leading to rapid cancer development, for example, in the colorectal cancer (CRC) mouse model, with the increase of E. coli, its metabolite LPS can upregulate the secretion of cathepsin K by CRC cells, which can induce M2 polarization of TAMs, leading to rapid CRC development (154), while a high-fat diet can induce gut microbiota dysbiosis, reduce SCFA levels, activate the MCP-1/C-C motif chemokine receptor 2 (CCR2) axis, and promote TAMs recruitment and polarization towards M2, ultimately leading to CRC development (155).