Akkermansia muciniphila-derived postbiotics reprogram immune balance to combat sepsis via the IDO1/Kyn/AhR metabolic axis

INTRODUCTION: Sepsis is a life-threatening syndrome of organ dysfunction driven by a dysregulated immune response. Effective therapeutic strategies to restore immune homeostasis remain limited. Hypoacylated lipooligosaccharides (ALOS) from Akkermansia muciniphila have emerged as potential immunomodulatory postbiotics, yet their therapeutic potential in sepsis and the underlying mechanisms remain unexplored. OBJECTIVES: This study aims to investigate whether ALOS confers protection in experimental models of sepsis induced by toxic lipopolysaccharides (LPS) or cecal ligation and puncture (CLP), and the mechanism by which ALOS exerts its anti-inflammatory and regulatory effects. METHODS: In LPS or CLP-induced mouse sepsis models and a porcine sepsis model, ALOS (0.2 mg/kg, i.p.) was administered once every two days before challenge or half an hour post-surgery. Survival rates, physiological and biochemical parameters were assessed. Based on 16S rRNA gene amplicon sequencing and barrier function assessment, the changes of the colonic microbiota and metabolites and anti-inflammatory capacity were analyzed. The anti-inflammatory and immunomodulatory mechanisms of ALOS were investigated through dendritic cell phenotyping, transcriptomic analysis, inhibitor assays, and conditioned medium experiments. Finally, the safety of ALOS was evaluated in C57BL/6J mice following one-week administration (0.2 mg/kg, i.p.). RESULTS: ALOS pretreatment significantly suppresses sepsis, reduces the proportion of pro-inflammatory Th17 cells, and increases regulatory T cells (Treg). Mechanistically, ALOS induced semi‑mature dendritic cells with upregulated IDO1 expression, leading to enhanced production of kynurenine (Kyn). Kyn activated the aryl hydrocarbon receptor (AhR) to drive Treg differentiation. The protective effect of ALOS was completely reversed by NLG919, whereas Kyn administration mimicked the therapeutic benefit. ALOS also produced therapeutic protection on sepsis. In a porcine sepsis model, pretreatment of ALOS exerted systemic anti‑inflammatory effects and protected multiple organs. CONCLUSION: This study highlights the protective role of ALOS in sepsis and identifies the IDO1-Kyn-AhR immune axis as the major underlying mechanism.