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A novel polysaccharide DG2 was obtained from the Dendrobium officinale endophytic fungus Fusarium solani DO7. The structural characterization and immunological activity of DG2 were investigated. Results showed that DG2 with the molecular weight of 152.8 kDa was composed of Galp, Manp, Glcp and Araf at a molar ratio of 4.3:1.9:2.8: 1.0. The main linkage types of DG2 were (1 → )-β-D-Glc, (1 → 4)-β-D-Glc, (1 → 3,6)-β-D-Gal and (1 → 6)-β-D-Gal, which demonstrated DG2 was a novel galactoglucan and different from other fungal and botanic polysaccharide. Furthermore, DG2 did not contain deoxynivalenol, and showed no direct toxicity to human embryonic kidney cells and RAW 264.7 cells. Meanwhile, DG2 could increase the TNF-α, IL-6 and iNOs mRNA expression levels of RAW264.7 cells, and further promote the production of TNF-α, IL-6 and NO. These results suggested DG2 could enhance macrophage-mediated immune responses and have the potential to be an attractive functional food supplement candidate for the hypoimmunity therapies.

Factors causing differences in immune activities between pectin and pectin-derived oligosaccharides have not been fully studied. In this article, four samples with different molecular weights and monosaccharide compositions, including polygalacturonic acid (poly-GA) and its oligosaccharide (oligo-GA), navel orange peel pectin (NP) and its oligosaccharide (oligo-NP), were used to compare their immunomodulatory properties on RAW264.7 cells. All samples had nontoxic effect on cells, oligo-GA and oligo-NP could increase the production of nitric oxide and cytokines to a much higher level than poly-GA and NP. The findings revealed that reducing the molecular weight and preserving the branched regions of pectin-derived samples could improve their immune-enhancing effects on macrophages. Interestingly, the addition of TAK-242 (TLR4 inhibitor) also demonstrated that the tested pectin oligosaccharides could stimulate the activation of macrophages through TLR4 signaling pathway. These results confirmed the potential value of pectin oligosaccharides, and provided theoretical support for their application in the pharmaceutical industry., Competing Interests: Declaration of competing interest No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part., (Copyright © 2022 Elsevier B.V. All rights reserved.)