Clostridia metabolites promote intestinal barrier integrity to protect from food allergy

Abstract We previously reported that a consortium of bacteria from the Clostridia class modulates intestinal barrier function through induction of IL-22 and prevents allergic sensitization to food in mice. We further investigated the properties of these bacteria and the mechanisms that underly their protective impact. Shotgun metagenomic sequencing of the anaerobically cultured Clostridia consortium identified genes which suggest the presence of flagellated bacteria. Motility was then confirmed using agar-based assays. Lysates generated from the consortium stimulated ileal tissue to produce IL-23 and IL-22 in vitro in a MyD88 and TLR5-dependent manner, specifically MyD88 signaling in CD11c+ cells. Together, these experiments support the presence of flagellin in our consortium. Flagellin is a TLR5 ligand that induces IL-23 production by CD11c+ dendritic cells, which stimulates IL-22 production in RORγt+ innate lymphoid cells (ILC3). In addition, we found that the Clostridia consortium produced indoles, known ligands for the aryl hydrocarbon receptor (AhR). In vitro stimulation of ileal tissue with indoles induced IL-22 production, and oral administration to antibiotic treated mice improved intestinal barrier function. Lastly, we observed impaired intestinal IL-22 production and barrier function, and exacerbated food allergy in mice that lack AhR signaling in RORγt+ cells such as ILC3, confirming the relevance of AhR signaling in our food allergy model. Production of flagellin and indoles are two potentially beneficial aspects of allergy-protective commensal bacteria and our knowledge of these pathways and metabolites will allow us to develop targeted therapeutics for the prevention or treatment of food allergy.