The Fragilysin-Induced Epithelial-Allergic Axis: How Enterotoxigenic Bacteroides fragilis (ETBF) Derails Oral Tolerance, and the Therapeutic Potential of Niacin/NAD+ Intervention

The Fragilysin-Induced Epithelial-Allergic Axis: How Enterotoxigenic Bacteroides fragilis (ETBF) Derails Oral Tolerance, and the Therapeutic Potential of Niacin/NAD+ Intervention

This manuscript introduces a novel, multidisciplinary mechanistic framework bridging microbiome pathogenesis, mucosal immunology, and nutritional bioenergetics. While the skyrocketing prevalence of adult-onset, IgE-mediated food allergies indicates a critical failure in the intestinal epithelial barrier, the exact upstream micro-ecological catalysts remain poorly defined. This paper hypothesizes a direct pathological link between the common colonic pathobiont Enterotoxigenic Bacteroides fragilis (ETBF) and the disruption of oral tolerance.

 

We map the precise molecular progression whereby ETBF-secreted fragilysin (BFT) anchors to claudin-4 and cleaves extracellular E-cadherin, opening an unmonitored paracellular gateway for intact dietary macromolecules. This structural dissolution initiates a profound intracellular signal: the nuclear translocation of \(\beta \)-catenin and the phosphorylation of STAT3. This transcriptional reprogramming drives a distinct epigenetic shift—suppressing miR-149-3p and upregulating miR-155—which triggers an aggressive interleukin storm (IL-8 and IL-17). This Th17-skewed mucosal microenvironment suppresses regulatory T cells (Tregs), forcing systemic IgE sensitization over protective IgG4 tolerance.

 

Crucially, we evaluate Niacin (Vitamin B3) as a targeted metabolic counterweight. By restoring the intracellular NAD+/SIRT1 pool and activating the GPR109A receptor, niacin suppresses STAT3 phosphorylation, rescues E-cadherin transcription, normalizes the mucosal microRNA profile, and stabilizes mast cells to mitigate IgE-mediated anaphylaxis. An experimental validation framework utilizing in vitro transwell co-cultures and gnotobiotic in vivo mouse models is proposed to verify this hypothesis.

Enterotoxigenic Bacteroides fragilis (ETBF); fragilysin (BFT); food allergy; claudin-4; E-cadherin; interleukins (IL-8/IL-17); microRNAs (miR-149-3p/miR-155); STAT3 signaling; niacin; oral tolerance; metainflammation; gut-lung axis.