Structure and immunostimulatory activity studies on two novel polysaccharides: revealing potential impacts of →6)-α-D-Glc(1→ on the TLR-4/MyD88/NF-κB pathway.

Two novel () polysaccharides, FVPH1 and FVPH2, were isolated and purified after hot water extraction. The structural characterization revealed that the backbone of FVPH1 consisted mainly of →6)-α-D-Glc(1→, →3,4)-α-D-Gal(1→, →4)-α-L-Fuc(1→, and →4)-β-D-Man(1→, while the backbone of FVPH2 consisted of →3)-α-D-Gal(1→, →3,4)-α-D-Man(1→,→6)-α-D-Glc(1→. The branches of FVPH1 contained →6)-α-D-Glc(1→ and α-D-Glc(1→ and the branches of FVPH2 consisted of →3)-α-D-Gal(1→, →6)-α-D-Glc(1→, and β-L-Fuc(1→. FVPH2 exhibited significantly better immunostimulatory activity than FVPH1 ( < 0.05), as evidenced by the increased expression of NO, IL-1β, IL-6, and TNF-α and pinocytic activity of RAW264.7 cells. As the most abundant structure in the polysaccharides of , the content of →6)-α-D-Glc(1→ might play a crucial role in influencing the immunostimulatory activity of polysaccharides. The polysaccharide with a lower content of →6)-α-D-Glc(1→ and a higher branching degree could significantly enhance the immunostimulatory activity of polysaccharides activating the TLR-4/MyD88/NF-κB pathway more effectively.