The gut microbiota influences the reactivity of the immune system, and Parabacteroides distasonis has emerged as an anti-inflammatory commensal. Here, we investigated whether its lysate could prevent severe forms of neuroinflammation in experimental autoimmune encephalomyelitis (EAE) in mice and how this preventive strategy affects the gut microbiota and immune response. Lysate of anaerobically cultured P. distasonis (Pd lysate) was orally administered to C57BL/6 mice in four weekly doses. One week later, EAE was induced and disease severity was assessed three weeks after induction. Fecal microbiota changes in both vehicle- and Pd lysate-treated animals was analyzed by 16S V3-V4 amplicon sequencing and qPCR, antimicrobial peptide expression in the intestinal mucosa was measured by qPCR, and immune cell composition in the mesenteric and inguinal lymph nodes was measured by multicolor flow cytometry. Pd lysate significantly delayed the development of EAE and reduced its severity when administered prior to disease induction. EAE induction was the main factor in altering the gut microbiota, decreasing the abundance of lactobacilli and segmented filamentous bacteria. Pd lysate significantly increased the intestinal abundance of the genera Anaerostipes, Parabacteroides and Prevotella, and altered the expression of antimicrobial peptides in the intestinal mucosa. It significantly increased the frequency of regulatory T cells, induced an anti-inflammatory milieu in mesenteric lymph nodes, and reduced the activation of T cells at the priming site. Pd lysate prevents severe forms of EAE by triggering a T regulatory response and modulating T cell priming to autoantigens. Pd lysate could thus be a future modulator of neuroinflammation that increases the resistance to multiple sclerosis.

• Keywords
• Parabacteroides distasonis, experimental autoimmune encephalomyelitis, inflammation, microbiota, multiple sclerosis, regulatory T cells,
• MeSH
• Bacteroidetes immunology   MeSH
• Encephalomyelitis, Autoimmune, Experimental * immunology   prevention & control   MeSH
• Mice, Inbred C57BL * MeSH
• Mice MeSH
• Gastrointestinal Microbiome * immunology   MeSH
• Intestinal Mucosa immunology   microbiology   metabolism   MeSH
• T-Lymphocytes immunology   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH

Multiple sclerosis is a debilitating autoimmune disease, characterized by chronic inflammation of the central nervous system. While the significance of the gut microbiome on multiple sclerosis pathogenesis is established, the underlining mechanisms are unknown. We found that serum levels of the microbial postbiotic tryptophan metabolite indole-3-carboxaldehyde (3-IAld) inversely correlated with disease duration in multiple sclerosis patients. Much like the host-derived tryptophan derivative L-Kynurenine, 3-IAld would bind and activate the Aryl hydrocarbon Receptor (AhR), which, in turn, controls endogenous tryptophan catabolic pathways. As a result, in peripheral lymph nodes, microbial 3-IAld, affected mast-cell tryptophan metabolism, forcing mast cells to produce serotonin via Tph1. We thus propose a protective role for AhR-mast-cell activation driven by the microbiome, whereby natural metabolites or postbiotics will have a physiological role in immune homeostasis and may act as therapeutic targets in autoimmune diseases.

• Keywords
• 3-IAld, Aryl hydrocarbon receptor, Mast cells, Multiple sclerosis, Serotonin,
• MeSH
• Kynurenine metabolism   MeSH
• Humans MeSH
• Ligands MeSH
• Receptors, Aryl Hydrocarbon metabolism   MeSH
• Multiple Sclerosis * MeSH
• Tryptophan * metabolism   MeSH
• Tryptophan Hydroxylase metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AHR protein, human MeSH Browser
• Kynurenine MeSH
• Ligands MeSH
• Receptors, Aryl Hydrocarbon MeSH
• TPH1 protein, human MeSH Browser
• Tryptophan * MeSH
• Tryptophan Hydroxylase MeSH