Fusobacterium nucleatum promotes M2 polarization of macrophages in the microenvironment of colorectal tumours via a TLR4-dependent mechanism

Fusobacterium nucleatum ( Fn ) has been shown to promote colorectal cancer (CRC) development by inhibiting host anti-tumour immunity. However, the impact of Fn infection on macrophage polarization and subsequent intestinal tumour formation as well as the underlying molecular pathways has not been investigated. We investigated the impact of Fn infection on macrophage polarization in human CRCs and cultured macrophages as well as the effects on macrophage phenotype and intestinal tumour formation in Apc Min/+ mice. We also examined whether macrophage-polarized activation challenged by Fn infection via a TLR4-dependent mechanism involved the IL-6/STAT3/c-MYC signalling cascade. Our data showed that macrophages are a major tumour-infiltrating immune cell type in human CRCs with Fn infection ( P