An arabinogalactan from Isatis indigotica and its adjuvant effects on H1N1 influenza and hepatitis B antigens

Isatis indigotica is an important medical herb in China and has been used for treating influenza and epidemic hepatitis for hundreds of years in China. In this study, an arabinogalactan (IIP-2) was firstly isolated from root of Isatis indigotica. Its chemical structure was identified and its adjuvant activity was investigated in mice co-immunised with H1N1 influenza vaccine or hepatitis B surface antigen (HBsAg). The results revealed that IIP-2 has a molecular weight of 66,400 Da and is composed of arabinose and galactose at a ratio of 1.0:1.5. Its structure contained a β-(1→3, 6)-galacan backbone. Pharmacological data demonstrated that IIP-2 could increase antigen-specific antibody levels in immunised mice. IIP-2-adjuvanted influenza or HBsAg vaccines improved proliferation of splenocytes and macrophages, stimulate cytokine productions. IIP-2 itself cannot show effects listed above. These results suggested that IIP-2-adjuvanted vaccines enhanced humoral and cellular immunity. IIP-2 could be developed as an efficacious adjuvant in human and animal vaccines.