LAUSR

Microbial metabolites such as short-chain fatty acids and aryl hydrocarbon receptor ligands shape host metabolism and immune functions. In Immunity, Macpherson and colleagues use stable isotope tracing of microbial and host metabolites to investigate the penetration of bacterial metabolites into host tissues, their transit through the host intestine, and the consequent immune and metabolic responses in the host. Transfer of labeled non-replicating Escherichia coli into fasting germ-free mice results in extensive penetration of a broad range of bacteriaderived molecules into most host tissues by 2 hours after transfer. The bacterial metabolites originate mostly from the small intestine, are cleared in the urine and have immunostimulatory effects. Mice lacking all antibody isotypes owing to deletion of the joining fragment in the immunoglobulin heavy chain have greater amounts of bacterial metabolites in some tissues than do wild-type mice, mostly as a result of the increased dwell time of the transferred bacteria in the small intestine, rather than loss of direct binding of antibodies to the bacterial metabolites. IV