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

A water-soluble polysaccharide (WSPA) was isolated with alkali and purified from the mature stem of Physalis alkekengi L. WSPA (M-w = 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 0-2 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. (C) 2014 Elsevier Ltd. All rights reserved.