Flagella and indole produced by commensal bacteria protect the intestinal barrier to prevent food allergy

Abstract Lifestyle-induced changes to the diversity of the commensal microbiota have been causally linked to the increasing prevalence of food allergies and other non-communicable chronic diseases. We have shown that bacteria from the Clostridia class prevent an allergic response to food by eliciting an IL-22 dependent barrier protective response that limits allergen access to the systemic circulation. We have now examined the mechanisms by which commensal Clostridia induce this allergy-protective effect. We identified taxa in a consortium of Clostridia that possess flagella and produce indole, which are ligands for TLR5 and AhR, respectively. Lysates and flagella isolated from this consortium induced IL-22 in mouse intestinal explants. IL-22 was not induced in explants from mice in which TLR5 or MyD88 was knocked out globally or conditionally in CD11c+ cells. Treatment with the commensal flagellar isolate also reduced detection of intragastrically administered FITC dextran in the serum of antibiotic-treated mice. Similarly, indole exposure induced IL-22 in intestinal explants and reduced intestinal permeability to FITC dextran. Importantly, AhR signaling in RORγt+ cells was necessary for IL-22 induction by flagella. These results suggest that flagella and indole act synergistically to prevent an allergic response. Finally, we have isolated and characterized two Clostridial taxa which bear flagella and produce indole. We hypothesize that germ-free mice colonized with these two taxa will exhibit improved IL-22 dependent barrier function and be protected against an allergic response. Our work reveals novel features of Clostridia key to their allergy-protective capability which may be further exploited to develop therapeutics. Supported by NIH AI106302 and the Bunning Professorship Endowment Fund