Lactiplantibacillus plantarum Mediated Tryptophan Metabolism to Alleviate Tropomyosin-induced Food Allergy.

Food allergy (FA) has become increasingly prevalent, affecting daily life. Probiotics alleviate FA by modulating immune-microbiome interactions. Nevertheless, the key metabolites and mechanisms by which L. plantarum alleviates FA remain unclear. In this study, L. plantarum demonstrated the ability to improve FA by modulating regulatory T/Th1/Th2 balance, modulating gut microbial composition, and regulating gut metabolites. Tropomyosin sensitization was associated with decreased levels of 5-hydroxyindole-3-acetic acid (5-HIAA) in cecum contents, a phenomenon also observed in the serum of FA mice and patients. In vitro experiments showed that tryptophan (Trp), tryptamine, tryptophol, kynurenine, 5-HIAA, and indole-3-acetamide inhibited RBL-2H3 cell degranulation; however, this inhibitory effect was attenuated by the aryl hydrocarbon receptor (AhR) antagonist CH223191. Moreover, in vivo results indicated that dietary supplementation with 5-HIAA or Trp downregulated IgE and cytokine levels in an AhR-dependent manner. This study provided evidence for the positive role of Trp metabolites in alleviating FA.