Intrahepatic microbes govern liver immunity by programming NKT cells

The gut microbiome shapes local and systemic immunity. The liver is presumed to be a protected sterile site. As such, a hepatic microbiome has not been examined. Here, we show that the liver hosts a robust microbiome in mice and humans that is distinct from the gut and is enriched in Proteobacteria. It undergoes dynamic alterations with age and is influenced by the environment and host physiology. Fecal microbial transfer experiments revealed that the liver microbiome is populated from the gut in a highly selective manner. Hepatic immunity is dependent on the microbiome, specifically Bacteroidetes species. Targeting Bacteroidetes with oral antibiotics reduced the hepatic immune cell infiltrate by ~90%, prevented APC maturation, and mitigated adaptive immunity. Mechanistically, presentation of Bacteroidetes-derived glycosphingolipids to NKT cells promotes CCL5 signaling, which drives hepatic leukocyte expansion and maturation. Collectively, we reveal a microbial – glycosphingolipid – NKT – CCL5 axis that underlies hepatic immunity. Overall design: CD45+ leukocytes were FACS-sorted from mouse livers after 1 week of treatment with oral antibiotics or vehicle.