Structural Characteristics and Gut Microbiota-Mediated Immunomodulatory Mechanisms of Water- and Alkali-Extracted...

Tuber indicum is a rare edible and medicinal ectomycorrhizal fungus, and the polysaccharide fractions have attracted extensive research attention owing to their potent immunomodulatory potential.

To systematically characterize the structural features and gut microbiota-mediated immunoregulatory mechanisms of water-extracted polysaccharide (TIWP) and alkali-extracted polysaccharide (TIAP) from T. indicum, two polysaccharide fractions were prepared and comprehensively structurally characterized in this study.

The maximum molecular weight of TIWP reached 2.65 × 10⁷ Da, which was dominated by glycosidic linkages of →3)-Glcp-(1→, →2,4)-Glcp-(1→ and →3,6)-Glcp-(1→. TIAP possessed a higher molecular weight up to 3.87 × 10⁷ Da, with predominant glycosidic bonds of →3,6)-Glcp-(1→, →4)-Glcp-(1→ and →2,4)-Glcp-(1→. In vivo bioactivity evaluation results demonstrated that both TIWP and TIAP significantly restored the proportions of CD3⁺ T and CD19⁺ B lymphocyte subsets in peripheral blood and spleen, and alleviated pathological damage in splenic and colonic tissues. Distinct regulatory patterns of gut microbiota were observed between the two polysaccharides: TIWP markedly enriched the genera Lactobacillus and Ruminiclostridium, whereas TIAP elevated the relative abundances of Lactobacillus and Alloprevotella. Untargeted metabolomics combined with KEGG pathway enrichment analysis revealed that TIWP and TIAP activated the pantothenic acid and coenzyme A biosynthesis pathway and the linoleic acid metabolism pathway.

Collectively, TIWP and TIAP alleviated CTX-triggered immunosuppression through distinct "gut microbiota-metabolite-immunity" regulatory networks due to their structural disparities. This study provides a theoretical basis for the development of gut microecology-targeted functional foods with immunomodulatory functions.