Recently, the immuno-enhancing potential of polysaccharide from Auricularia auricula (AAP) has been an area of research interest. However, the immune-stimulatory activity and mechanisms of AAP in immunosuppressive mice treated with cyclophosphamide (CTX) are still poorly understood. This study aimed to evaluate the immuno-enhancing effects of AAP and mine its possible mechanisms. Firstly, polysaccharides were isolated from A. auricula and purified. Secondly, the immune-stimulatory activities of the first AAP fraction (AAP1) were evaluated in the CTX-treated mice. Results showed that AAP1 significantly enhanced immune organ indexes, remarkably stimulated IFN-g, IL-2, IL-4, IL-10, and TNF-a levels in the serum, and dramatically up-regulated the mRNA levels of Claudin-1, Occludin and ZO-1. Compared to the CTX group, AAP1 administration restored the gut microbiota composition similar to that of the control group by decreasing the ratio of Firmicutes/Bacteroidetes and increasing the relative abundances of short-chain fatty acid-producing microbiota. This study provides useful information for its further application as an immune-stimulator in foods and drugs.

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Assessments of molecular weight distribution and activity/efficacy of Auricularia heimuer polysaccharides (AAP) are of substantial significance for its extraction process optimisation. In the present study, single-factor orthogonal test and response surface methodology were employed to optimise extraction conditions of AAP. Furthermore, a rat hyperlipidaemia model was established to compare the lipid-lowering activity of polysaccharides obtained by three extraction methods. Conditions for enzymatic hydrolysis were optimised as pH 5.0, 1% cellulase, 2.5% substrate concentration and enzymolysis time of 1.5 h, leading to an up to 31.8% polysaccharide yield and 89.13% of polysaccharides within the molecular weight range of 5 000 Da to 10 000 Da. The results of animal experiments showed that the lipid-lowering activity of enzymolysis-extracted polysaccharides was significantly higher than that of water- and ultrasonic-extracted ones (P < 0.01). So the present study revealed that enzymatic hydrolysis-extracted polysaccharides showed the strongest hypolipidaemia activity, providing a basis for the development of A. heimuer-based functional foods and drugs.

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