Potential structure-immunostimulatory activity relationship of Tartary buckwheat sprout pectic polysaccharides: Influences of molecular mass and esterification degree.

Tartary buckwheat sprout pectic polysaccharides (TP) have demonstrated notable immunostimulatory activity in vitro. Nevertheless, the in vivo function and how structural features dictate its immunostimulatory activity through gut microbiota modulation are still unclear. To fill this gap in our understanding, we compared in vivo immunostimulatory effects of TP and its derivatives featuring key structural modifications: a lower esterification degree (TP-LDE: 4.72% vs. TP: 28.04%) or a lower molecular mass (TP-LMW: 0.957 × 104 Da vs. TP: 8.191 × 104 Da). Results demonstrated that TP and its derivatives (TP-LDE, TP-LMW) counteracted cyclophosphamide (CTX)-induced immunosuppression by restoring gut microbiota balance, short-chain fatty acid (SCFA) levels, intestinal barrier function, and systemic immunity. Notably, the derivatives, particularly TP-LMW, exhibited superior immunostimulatory activity to the native TP in enhancing serum cytokines (TNF-α and IFN-γ) and serum immunoglobulin IgA, promoting SCFA (propionic acid and butyric acid) production, and maintaining intestinal barrier function (enhanced expression of ZO-1 and occludin), confirming that reducing either the molecular mass or the esterification degree enhances TP's immunostimulatory potency. Furthermore, all treatments reversed CTX-induced dysbiosis by increasing Muribaculaceae while suppressing dysbiosis-linked genera (e.g., Lachnospiraceae_NK4A136_group, Colidextribacter, and Oscillibacter). In contrast, only TP-LDE uniquely and significantly enriched the beneficial genera Bacteroides, Prevotellaceae_UCG_001, and Parabacteroides. Taken together, this work elucidates how structural features govern the immunostimulatory activity of TP, which provides a foundation for developing TP and its derivatives into functional foods for improving and maintaining host immunity.