Preparation of Auricularia auricula-Derived Immune Modulators and Alleviation of Cyclophosphamide-Induced Immune Suppression and Intestinal Microbiota Dysbiosis in Mice

With the acceleration of the pace of life, increased stress levels, and changes in lifestyle factors such as diet and exercise, the incidence of diseases such as cancer and immunodeficiency has been on the rise, which is closely associated with the impaired antioxidant capacity of the body. Polypeptides and polysaccharides derived from edible fungi demonstrate significant strong antioxidant activity and immunomodulatory effects. <i>Auricularia auricula</i>, the second most cultivated mushroom in China, is not only nutritionally rich but also offers considerable health benefits. In particular, its polysaccharides have been widely recognized for their immunomodulatory activities, while its abundant protein content holds great promise as a raw material for developing immunomodulatory peptides. To meet the demand for high-value utilization of <i>Auricularia auricula</i> resources, this study developed a key technology for the stepwise extraction of polypeptides (AAPP1) and polysaccharides (AAPS3) using a composite enzymatic hydrolysis process. Their antioxidant and immunomodulatory effects were assessed using cyclophosphamide (CTX)-induced immune-suppressed mice. The results showed that both AAPP1 and AAPS3 significantly reversed CTX-induced decreases in thymus and spleen indices (<i>p</i> < 0.05); upregulated serum levels of cytokines (e.g., IL-4, TNF-α) and immunoglobulins (e.g., IgA, IgG); enhanced the activities of hepatic antioxidant enzymes SOD and CAT (<i>p</i> < 0.05); and reduced the content of MDA, a marker of oxidative damage. Intestinal microbiota analysis revealed that these compounds restored CTX-induced reductions in microbial α-diversity, increased the abundance of beneficial bacteria (<i>Paramuribaculum</i>, <i>Prevotella</i>; <i>p</i> < 0.05), decreased the proportion of pro-inflammatory <i>Duncaniella</i>, and reshaped the balance of the Bacteroidota/Firmicutes phyla. This study represents the first instance of synergistic extraction of polypeptides and polysaccharides from <i>Auricularia auricula</i> using a single process. It demonstrates their immune-enhancing effects through multiple mechanisms, including "antioxidation-immune organ repair-intestinal microbiota regulation." The findings offer a theoretical and technical foundation for the deep processing of <i>Auricularia auricula</i> and the development of functional foods.