Water-soluble polysaccharide isolated with alkali from the stem of Physalis alkekengi L.: Structural characterization and immunologic enhancement in DNA vaccine

• Structure of WSPA was analyzed.
• WSPA significantly enhanced specific antibody titers IgG, IgG1and IgG2b in mice immunized with DNA vaccine.
• DNA vaccine pD-HSP90C evoked the production of specific antibody.

A water-soluble polysaccharide (WSPA) was isolated with alkali and purified from the mature stem of Physalis alkekengi L. WSPA (Mw = 31 kDa) was an acid heteropolysaccharide, which consisted of Rha, Ara, Xyl, Gal, Glc and GalA in ratio of 1.0:2.5:0.8:2.7:4.4:1.4. The results from structural analysis indicated backbone and branches of WSPA were composed of (1 → 3)-linked Glc, (1 → 3)-linked Gal, (1 → 2)-linked Xyl, (1 → 2)-linked Ara, and (1 → 2)-linked Rha residues. However, GalA was distributed only in the backbone of WSPA. All branches of WSPA were at O-2 of (1 → 6)-linked Gal and terminated with Glc. More importantly, it was found that WSPA significantly enhanced specific antibody IgG response with higher titers of IgG1 as well as IgG2b (p < 0.05) in mice immunized with DNA vaccine. Therefore, WSPA can be considered as a potential adjuvant candidate in DNA vaccine.

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