CXCL16 and liver cancer: Secondary bile acids produced by gut microbiota decreased CXCL16 (the only ligand for CXCR6 (CXC Receptor 6)) expression on hepatocyte surface, demonstrated by higher levels of CXCL16 mRNA in the liver of germ-free mice (about twice), which prevent the aggregation and immune monitoring of CXCR6+ T-cells, thereby causing liver cancer.