A structurally defined acidic Angelica sinensis polysaccharide synergizes with αGalCer as adjuvants to enhance humoral and cellular immunity.

The development of effective adjuvants is important for enhancing subunit vaccine efficacy. A novel acidic polysaccharide (ASP-3b) was isolated and purified from Angelica sinensis roots. We characterized its structure and evaluated its potential as a vaccine adjuvant, particularly in synergy with the glycolipid α-galactosylceramide (αGalCer or αGC). ASP-3b is a pectin polysaccharide with a molecular weight of 346,628 Da. It was composed of rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, and arabinose in a molar ratio of 2.16: 1.84:78.21:1.24:11.23:5.32. Structural analyses revealed that ASP-3b was an HG-RG-I type pectin polysaccharide with →4)-α-D-GalpA-(1 → and →4)-α-D-GalpA-(1 → 2)-α-L-Rhap-(1 → as the main backbone linkages, in which the 1,2-α-Rhap residues substituted at O-4 by 1,3-β-Galp, 1,5-α-Araf, and 1,4-β-Galp side chains. In vitro, ASP-3b significantly promoted the maturation of DC2.4. In vivo, a liposome co-delivering ASP-3b, αGC and OVA elicited markedly synergistic effects. Compared with single-adjuvant vaccines, the ASP-3b/αGC dual-adjuvant vaccine enhanced splenic antigen-presenting cell (APC) activation, induced potent antigen-specific humoral immunity, and elicited strong cellular immunity. To our knowledge, this is the first report of a synergistic dual-adjuvant system combining a plant-derived polysaccharide with an iNKT cell agonist, providing a promising strategy for enhancing the immunogenicity of subunit vaccines.