Immunomodulatory mechanisms of an acidic polysaccharide from the fermented burdock residue by Rhizopus nigricans in RAW264.7 cells and cyclophosphamide-induced immunosuppressive mice

RBAPS is an acidic polysaccharide extracted from the burdock residue fermentation by Rhizopus nigricans. In RBAPS-activated RAW264.7 cells, transcriptome analysis identified a total of 1520 differentially expressed genes (DEGs), including 1223 down-regulated genes and 297 up-regulated genes. DEGs were enriched in the immune-related biological processes, involving in Mitogen-activated protein kinase (MAPK) and Toll-like receptor (TLR) signaling pathway, according to Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The results of the confocal laser scanning microscope (CLSM) observation, antibody neutralization and Western blot verified that RBAPS modulated macrophages activation and cytokines secretion mainly via TLR4/MAPK/NF-κB signaling pathway. The immunomodulatory activity in vivo of RBAPS was investigated in cyclophosphamide (CTX)-induced immunosuppressive mice. RBAPS promoted the counts of white blood cells (WBC), red blood cells (RBC) and platelets (PLT) as well as the levels of immunoglobulins and cytokines (IgG, IgM, TNF-α, and IL-2) in immunosuppressive mice. RBAPS protected the spleen and thymus from CTX-induced injury by increasing the organ indexes, attenuating pathological damage, and promoting splenic lymphocytes proliferation. Importantly, RBAPS ameliorated the intestine integrity and function by promoting the expression of Occuldin, Claudin-5, Atg5, and Atg7, activating TLR4/MAPK signaling pathway in CTX-induced mice. This study suggested that RBAPS was a prime candidate of immunologic adjuvant in chemotherapy for the nutraceutical and pharmaceutical application.