Effects of alkali dissociation on the molecular conformation and immunomodulatory activity of longan pulp polysaccharide (LPI)

The effects of alkali dissociation on the molecular conformation and immunomodulatory activity of longan pulp polysaccharide (LPI) were investigated to explore their possible relationship. The molecular conformations of LPI and its degraded derivatives (LPI1 and LPI2) were examined by size exclusion chromatography combined with multi-angle laser light scattering (SEC-MALLS), Congo red test and atomic force microscopy (AFM). The results confirmed the transformation of LPI from compact sphere-like conformation to slightly dissociated sphere-like conformation (LPI1) or single-helix chain (LPI2). Compared with the control, splenocyte proliferation and NK cell cytotoxicity were significantly enhanced by LPI1 and LPI2 (P < 0.05), although they were not stimulated by LPI in 100–400 μg/mL (P > 0.05). All the polysaccharides could significantly enhance macrophage phagocytosis at 100 or 200 μg/mL (P < 0.05). Single-helix chain might play an important role in activating lymphocytes and NK cells, but having weak contribution to macrophage phagocytosis.