Insight into the structural and immunomodulatory relationships of polysaccharides from Dendrobium officinale-an in vivo study

To understand the structural and immunomodulatory relationships of Dendrobium officinale polysaccharide (DOP), ultrasonic (UDOP-1 and UDOP-2) and alkaline treatments (DADOP-1 and DADOP-2) were used to obtain DOPs of varied Mw and degrees of acetylation (DA). In vivo mice study indicated that the DOP by ultrasonic degradation and deacetylation modification could differentially restore the organ indexes, improve immune response, enhance the release of cytokine and modulate the structure of gut microbiota in Cy-induced immunosuppressed mice. The degree of immune activity recovery was decreased in the order of UDOP-2 > DADOP-1 > DOP > UDOP-1 > DADOP-2. Structurally, the Mw of UDOP-2 decreased from 649 kDa to 279 kDa, and DA decreased from 8.87% to 3.68% after ultrasonication treatment. These results suggested that the short-time ultrasonication process could enhance the immune activity. The polysaccharide fractions with similar acetyl group content but lower Mw had a strong enhancement in their immune activity in vivo. In contrast, the low acetyl content was not conducive to enhancing immune activity, suggesting that a certain acetyl content may be a key factor for the immune activity of DOP, but the range of DA value still needs to be further explored.