An α-glucan isolated from root of Isatis Indigotica, its structure and adjuvant activity

The root of Isatis indigotica is a traditional Chinese herbal medicine. An α-glucan (IIP-A-1) was firstly isolated from the roots. In this study we elucidated the chemical structure of IIP-A-1 and determined its adjuvant activity by co-immunizing mice with H1N1 influenza virus split and recombinant hepatitis B surface antigen (HBsAg), respectively. The polysaccharide was pretreated with periodate oxidation, Smith degradation and methylation in order to analyze its structure using GC, HPGPC, FT-IR, NMR and GC-MS. The adjuvant effect was evaluated by determining the antibody titers of serum against H1N1 influenza and HBsAg using ELISA. The proliferation and TNF-α secretion of macrophages administrated with different dose of IIP-A-1 were measured in vitro. The results of this study revealed that IIP-A-1 was an α-glucan with the molecular weight of 3,600 Da. The backbone was α-(1 → 4)-D-glucan with (1 → 6) branch chain. The α-glucan could significantly enhance the immune response of mice immunized with H1N1 influenza or HBsAg in vivo and exert good dose-dependent effects on the proliferation and the TNF-α secretion of macrophages in vitro. These results supported that IIP-A-1 was expected to be an efficacious adjuvant candidate for prophylactic and therapeutic vaccines.