Regulation of host immune responses by Lactobacillus through aryl hydrocarbon receptors

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that serves as a key environmental sensor and mechanistic regulator of both the epithelial barrier and systemic immunity. Exogenous ligands (aromatic compounds such as dioxins) and endogenous ligands (tryptophan and its metabolite family) are the two types of AhR ligands. In particular, certain gut flora contain enzymes involved in the metabolism of tryptophan to AhR ligands, and Lactobacillus is attractive among all intestinal flora which are capable of producing AhR ligands. This research reviews the probiotic effects of Lactobacillus reuteri and other Lactobacilli on immunological responses and gut barrier function via the AhR pathway, and it also provides evidence to support the probiotics as an alternative therapy for some specific diseases in the future.