Structural characterization of low molecular weight polysaccharide from Astragalus membranaceus and its immunologic enhancement in recombinant protein vaccine against systemic candidiasis

•Structure of LMw-ASP is analyzed.•LMW-ASP enhances significantly specific antibody titers IgG, IgG1and IgG2b.•LMW-ASP promotes significantly production of IL-2, IL-4, IL-10, IL-12 in sera of mice.•LMW-ASP reduces significantly the numbers of CFU in the kidneys of mice.•LMw-ASP may be an adjuvant which greatly improved Th1 and Th2 responses in recombinant protein rP-HSP90C.

Structure and immunologic enhancement of low molecular weight polysaccharide (LMW-ASP) isolated from the root of Astragalus membranaceus (Fisch) Bge. Were detected in recombinant protein vaccine. Structure analysis of LMW-ASP revealed that LMW-ASP (Mw = 5.6 kDa) was an acid heteropolysaccharide, which consisted of Glc, Gal, Ara, Xyl and GalA in ratio of 10.0：1.3：1.7：1.0：0.9. Recombinant protein (rP-HSP90C) contained epitope C (LKVIRK) from heat shock protein 90 (HSP90) of Candida albicans was used as a vaccine. The results indicated that LMW-ASP significantly promoted specific antibody titers IgG, IgG1, IgG2b, and IL-2, IL-4, IL-10, IL-12 in sera of mice immunized with rP-HSP90C (p < 0.05). It was also found LMW-ASP improved DTH response in HSP90C-injceted mice. More importantly, the mice immunized with rP-HSP90C/LMW-ASP had fewer CFU (colony forming unites) in the kidneys compared to the mice immunized with rP-HSP90C (p < 0.05). Therefore, LMW-ASP could be exploited into the novel adjuvant to enhance the efficacy of recombinant protein vaccine.