Dietary chitosan oligosaccharides enhance resistance to Salmonella infection by rewiring microbiota derived indole AhR IgA immunity

Chitosan oligosaccharide (COS) protects against Salmonella Typhimurium infection by altering the gut microbiome. This change increases levels of the bacterium Ligilactobacillus and the gut metabolite indole-3-carboxylic acid (I3CA). I3CA then activates the aryl hydrocarbon receptor (AhR) to boost IgA antibody production, strengthening the gut's immune defense. The protection requires an intact gut microbiota, showing that COS works by modifying microbial metabolism to enhance host immunity.