Mechanism of Intestinal Flora and Proteomics on Regulating Immune Function of Durio zibethinus Rind Polysaccharide

In this study, cyclophosphamide was injected intraperitoneally to establish an immunosuppressive mouse model to study the immune regulating effects of Durio zibethinus Murr rind polysaccharide (DZMP) through proteomics and intestinal flora. The results showed that the thymus and spleen indexes of the high-dose DZMP (200 mg/kg) group were significantly increased, and the tissue structure of the spleen was improved compared with the model group ( $P<0.01$ ). The contents of IL-2, IL-4, IL-6, and TNF-α in the high-dose group of DZMP were significantly increased ( $P<0.001$ ). Activities of acid phosphatase (ACP), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) were increased in serum ( $P<0.01$ ). In the liver, catalase (CAT) activity was increased ( $P<0.001$ ) while the malondialdehyde (MDA) content was decreased and immune activity was increased ( $P<0.001$ ). Proteomics studies showed that the drug group could significantly increase the low-affinity immunoglobulin gamma Fc receptor III (FcγRIII) protein and protein kinase C-α (PKC-α) compared with the model group ( $P<0.001$ ). In addition, the result showed that those proteins were likely involved in the regulation of the metabolic pathways of autoimmune thyroid disease, Staphylococcus aureus infection, and NF-κB signaling pathway. Intestinal microbial studies showed that short-chain fatty acid (SCFA) content was increased as well as the relative abundance of beneficial bacteria Akkermansia, Bacteroides, and Paraprevotella, while the relative abundance of Ruminococcus and Oscillospira was decreased compared with the model group ( $P<0.001$ ). The results showed that DZMP might play a beneficial role in immune regulation by improving intestinal flora.